Zoom Lens System

1. Field of the Invention

The present invention relates to a zoom lens and, more particularly, to a zoom lens attached to a so-called auto-focusing camera, video camera, or the like, which has a focus detection device, and moves a focusing lens unit in a photographing optical system in accordance with the detected defocus amount.

2. Related Background Art

In recent years, along with the wide spread use of auto-focusing cameras, various focusing systems such as a so-called inner focusing system, rear focusing system, and the like have been examined to make a focusing lens of a zoom lens compact.

However, in general, when a focusing system other than a so-called front focusing system is adopted, the lens driving amount for focusing changes upon a change in focal length. To solve this problem, Japanese Patent Application Laid-Open Nos. 4-293008 and 5-142475 assigned to the same assignee as the present invention proposed a method of realizing a so-called manual focusing operation in a zoom lens having a plurality of lens units including a focusing lens unit having both zooming and focusing functions. In this method, when a predetermined movement locus for zooming is expressed by the amount of movement of the lens units in the direction of the optical axis and the angle of rotation of a rotatable lens barrel, the movement locus of the focusing lens unit is defined by synthesizing a focus cam and a zoom compensation cam. With this arrangement, even when the amount of movement for focusing along the optical axis changes depending on the zooming state, the angle of rotation of the rotatable lens barrel for focusing is left unchanged, thus achieving a manual focusing operation.

However, when the above-mentioned zoom lens is applied to an auto-focusing camera system, which comprises focus detection means, storage means for storing the conversion coefficient .gamma. and the correction coefficient .epsilon. used for calculating the lens driving amount .DELTA.x for focusing the focusing lens unit on the basis of the detected defocus amount .DELTA.Bf of a photographing optical system, and calculation means for calculating the lens driving amount .DELTA.x for focusing using the defocus amount .DELTA.Bf, the conversion coefficient .gamma., and the correction coefficient .epsilon., problems associated with the storage capacity, calculation error, and the like are posed.

As in Japanese Patent Application Laid-Open Nos. 4-293008 and 5-142475 above, in a zoom lens disclosed in Japanese Patent Application Laid-Open Nos. 57-37307, 57-37308, 63-49715, 63-314511, 3-144411, 3-235908, 3-249717, 4-184402, 4-184403, 4-184404, 4-184405, 4-184406, 4-186207, 4-186208, 7-110446, and the like, in each of which the movement locus of the focusing lens unit is defined by synthesizing a focus cam and a zoom compensation cam, the above-mentioned problems concerning the storage capacity, calculation error, and the like have not been examined, either.

Furthermore, in a zoom lens disclosed in Japanese Patent Application Laid-Open Nos. 57-4018, 58-137812, 58-137814, 58-144808, 58-149014, 58-150925, and the like, each of which utilizes only a focus cam, the problems of the storage capacity, calculation error, and the like have not been examined, either.

On the other hand, as in Japanese Patent Application Laid-Open Nos. 63-163808, 1-154014, and the like assigned to the same assignee as the present invention, in a zoom lens disclosed in Japanese Patent Application Laid-Open Nos. 64-35515, 64-35516, 4-140704, and the like, each of which commonly uses a single cam as both a focus cam and a zoom cam, the above-mentioned problems of the storage capacity, calculation error, and the like have not been examined, either. In addition, the zoom lens disclosed in these references has a basic structure different from that of the present invention since it does not require any zoom compensation cam, and does not take a so-called flexible manual focusing operation into account, which has been examined in Japanese Patent Application Laid-Open Nos. 4-293008, 5-142475, and the like.

A zoom lens disclosed in Japanese Patent Application Laid-Open Nos. 2-256011 and 3-101707 which have been assigned to the same assignee as the present invention, and Japanese Patent Application Laid-Open No. 7-120662 which discloses a technical content similar to those disclosed in the above Japanese Patent Application Laid-Open Nos. 2-256011 and 3-101707, has a basic structure different from that of the present invention since it realizes zooming by a relative movement, in the direction of rotation of a lens barrel, between a focus cam and a zoom cam, and focusing by a relative movement in the direction of the optical axis, and does not examine an auto-focusing operation at all.

Similarly, in Japanese Patent Application Laid-Open No. 7-5362, a zoom lens disclosed therein has a basic structure different from that of the present invention since the amount of movement for focusing is to be defined by synthesizing -two kinds of cams without using a focus cam directly, and the above-mentioned problems concerning the storage capacity, calculation error, and the like have not been examined.

Furthermore, Japanese Patent Application Laid-Open Nos. 61-77027, 1-232313, and the like disclose a lens system having a focus cam so as to realize an accurate auto-focusing operation with a small calculation error. However, these references relate to a single-focus lens having no zooming function, and cannot be applied to a focus cam required to achieve a so-called manual focusing operation in a zoom lens in which the amount of movement in the direction of the optical axis for focusing changes depending on the zooming state.

The principle of the auto-focus operation will be briefly described below.

An auto-focusing system disclosed in Japanese Patent Application Laid-Open Nos. 62-78519, 62-170924, 1-131507, 1-131508, 1-131509, 3-228006, and the like, comprises focus detection means, calculation means for calculating the lens driving amount for focusing, and storage means for storing specific constants used in calculations. In this system, the focus detection means detects the defocus amount .DELTA.Bf between the imaging position of an actual object by the photographing optical system and a predetermined imaging point position, and the calculation means for calculating the lens driving amount for focusing calculates the lens driving amount .DELTA.x for focusing on the basis of the detected defocus amount .DELTA.Bf of the photographing optical system, thus achieving an auto-focusing operation.

If the relationship between the lens driving amount .DELTA.x for focusing and the defocus amount .DELTA.Bf is expressed using a conversion coefficient K associated with focusing as follows:

then, the lens driving amount Ax can be calculated by setting the conversion coefficient K.

However, as described in Japanese Patent Application Laid-Open No. 62-170924, the conversion coefficient K changes in correspondence not only with the focal length but also with the object position and lens arrangement.

Therefore, as described in Japanese Patent Application Laid-Open Nos. 62-78519, 62-170924, and the like, using the conversion coefficient .gamma. defined as the ratio (sensitivity) of the amount of infinitesimal movement of the imaging plane with respect to the amount of infinitesimal movement of the focusing lens unit in the vicinity of a predetermined in-focus point, and the correction coefficient .epsilon. for correcting the conversion coefficient in accordance with the defocus amount .DELTA.Bf, the conversion coefficient K is calculated by the following formulas:

and thereafter, the lens driving amount .DELTA.x is calculated based on the conversion coefficient K. (Of course, the lens driving amount .DELTA.x for focusing may be directly calculated from the defocus amount .DELTA.Bf using the conversion coefficient y and the correction coefficient .epsilon..) Furthermore, in a photographing system having a zooming optical system, since the values of the conversion coefficient .gamma. and the correction coefficient .epsilon. change depending on the lens arrangement, a plurality of pairs of data of the conversion coefficient .gamma. and the correction coefficient .epsilon. are stored in the storage means in units of a plurality of divided zoom ranges and focus ranges, as described in Japanese Patent Application Laid-Open No. 3-228006.

In other words, in the photographing system having the zooming optical system, the focus detection means detects the defocus amount .DELTA.Bf caused by the zooming optical system, and values of the conversion coefficient .gamma. and the correction coefficient .epsilon. corresponding to the zoom and focus positions respectively detected by zoom and focus position detection means are read out from the storage means. The calculation means for calculating the lens driving amount for focusing calculates the lens driving amount .DELTA.x for focusing using the defocus amount .DELTA.Bf, the conversion coefficient .gamma., and the correction coefficient .epsilon., and driving means drives a lens by the calculated lens driving amount .DELTA.x for focusing, thus achieving a focusing operation.

However, in a normal focusing mechanism using a helicoid mechanism or a cam mechanism, the lens driving amount for focusing must be described not as a lens driving amount .DELTA.x in the direction of the optical axis but as a lens driving amount .DELTA.a in the direction of rotation.

Therefore, when the relationship between the lens driving amount .DELTA.x and the defocus amount .DELTA.Bf in the direction of the optical axis is converted into the relationship between the lens driving amount .DELTA.a and the defocus amount .DELTA.Bf in the direction of rotation using a conversion coefficient K.sub.a associated with the direction of rotation, we have:

If conversion coefficient K associated with the direction of the optical axis is newly defined as K.sub.x, the conversion coefficient K.sub.a associated with the direction of rotation is expressed using a conversion coefficient .PHI. between the lens driving amount .DELTA.x in the direction of the optical axis and the lens driving amount .DELTA.a in the direction of rotation as follows:

Thus, the formula in Japanese Patent Application Laid-Open No. 62-170924 is modified to a formula associated with the conversion coefficient K.sub.a in the direction of rotation as follows:

If .DELTA.x and .DELTA.a have a linear relationship therebetween like in a helicoid mechanism, .PHI. becomes a constant. However, when a cam mechanism is used, the conversion coefficient .PHI. changes depending on the cam shape. The conversion coefficient .PHI. can be replaced by a slope (dx/da) defined by the cam shape as follows:

The conversion coefficient .gamma. and the correction coefficient .epsilon. in an inner focusing type zoom lens disclosed in Japanese Patent Application Laid-Open Nos. 4-293008, 5-142475, and the like will be examined below.

When a zoom lens system is constituted by n lens units, and its k-th lens unit is used as the focusing lens unit, if the ratio of the amount dBf of infinitesimal movement of the imaging plane to the amount dx of infinitesimal movement, in the direction of the optical axis, of the focusing lens unit, i.e., the conversion coefficient .epsilon. (dBf/dx: the sensitivity associated with movement in the direction of the optical axis) is defined as a new conversion coefficient .gamma..sub.x associated with the amount x of movement in the direction of the optical axis, the conversion coefficient .gamma..sub.x can be expressed using the imaging magnifications .beta. of the respective lens units as follows:

Therefore, the rate of change, from the infinity in-focus value (.gamma..sub.xO) to the closest in-focus value (.gamma..sub.xR), of the conversion coefficient .gamma..sub.x associated with the amount x of movement in the direction of the optical axis can be expressed using the imaging magnifications .beta..sub.Ok and .beta..sub.Rk of the focusing lens unit at the infinity and closest in-focus points as follows:

Furthermore, if the ratio of the amount dBf of infinitesimal movement of the imaging plane to the angle da of infinitesimal rotation of the focusing lens unit (dBf/da: the sensitivity associated with movement in the direction of rotation) is defined as a new conversion coefficient .gamma..sub.a associated with the angle a of rotation of a rotatable lens barrel, the conversion coefficient .gamma..sub.a associated with the angle a of rotation of the rotatable lens barrel can be expressed by:

where dx/da is the slope of the focus cam.

Therefore, the rate of change, from the infinity in-focus value (.gamma..sub.aO) to the closest in-focus value (.gamma..sub.aR), of the conversion coefficient .gamma..sub.a associated with the angle a of rotation of the rotatable lens barrel can be expressed using slopes (dx/da).sub.O and (dx/da).sub.R at the infinity and closest corresponding positions on the focus cam as follows:

The rate of change of the conversion coefficient .gamma..sub.x with respect to the amount x of movement in the direction of the optical axis and the rate of change of the conversion coefficient .gamma..sub.a with respect to the angle a of rotation of the rotatable lens barrel will be examined below in association with an embodiment of Japanese Patent Application laid-Open No. 5-142475. Note that the amount of rotation for zooming from the wide-angle end to the telephoto end and the amount of rotation for focusing are respectively re-set to be 10.0 for the purpose of a comparison with an embodiment of the present invention.

Table 1 below summarizes various paraxial data of an optical system and data for defining the shape of the focus cam corresponding to the embodiment of Japanese Patent Application Laid-Open No. 5-142475.

The upper table in Table 1 summarizes the focal length data and principal point interval data of the respective lens units of the optical system corresponding to the embodiment of Japanese Patent Application Laid-Open No. 5-142475. In this table, F1, F2, F3, and F4 are respectively the focal lengths of first, second, third and fourth lens units, and D1, D2, D3, and D4 are respectively the principal point interval between the first and second lens units, the principal point interval between the second and third lens units, the principal point interval between the third and fourth lens units, and the principal point interval between the fourth lens unit and a predetermined imaging plane in six zooming states (focal lengths F=36.0 (1-POS), 50.0 (2-POS), 60.0 (3-POS), 70.0 (4-POS), 85.0 (5-POS), and 103.0 mm (6-POS)).

The middle table in Table 1 summarizes spline sample point data when the shape of the focus cam in the second lens unit which is used for focusing is expressed by a spline function associated with the angle a of rotation of the rotatable lens barrel and the amount x of movement in the direction of the optical axis (complying with "Numerical Analysis and FORTRAN", MARUZEN, "Spline Function and Its Applications", Kyoiku Shuppan, and the like). In this middle table, (1), (2), (3), and (4) correspond to the first, second, third, and fourth lens units, respectively.

Furthermore, the lower table in Table 1 summarizes the infinity focusing positions (infinity corresponding positions) at the respective focal lengths (F=36.0, 50.0, 60.0, 70.0, 85.0, and 103.0 mm), and the amounts of rotation (amounts of rotation for focusing) upon focusing to respective photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m) using the focus cam. Since both the amount of rotation for zooming from the wide-angle end (F=36.0) to the telephoto end (F=103.0) and the amount of rotation for focusing from the infinity in-focus position to the closest in-focus position (R=0.85 m) are 10.0, the rotation amount ratio (a.sub.F /a.sub.Z) of the amount of rotation for focusing to the amount of rotation for zooming is 1.0.

Table 2 below summarizes the numerical value data of the cams of the focusing lens unit in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, which data are calculated by interpolation based on a spline function on the basis of the sample data of the focus cam summarized in the middle table in Table 1. In this table, (ANGLE) is the angle of rotation of the rotatable lens barrel, (2) is the amount (mm) of movement, in the direction of the optical axis, of the second lens unit, and (F) is the focal length (mm) of the entire system in an infinity in-focus state corresponding to the amount (ANGLE) of rotation.

The left table in Table 2 summarizes the numerical value data of the focus cam in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, and the right table in Table 2 summarizes the numerical value data of the zoom compensation cam of the embodiment. A value obtained by synthesizing the amount (2) of movement in the direction of the optical axis in the numerical value data of the focus cam and the amount (2) of movement in the direction of the optical axis in the numerical value data of the zoom compensation cam in a range from the amount of rotation (ANGLE=0.0) to the amount of rotation (ANGLE=10.0) agrees with the movement locus of the second lens unit calculated using the paraxial data in the upper table in Table 1.

Tables 3, 4, and 5 below summarize the amount DX (mm) of movement for focusing, in the direction of the optical axis, of the focusing lens unit, the imaging magnifications .beta..sub.K of the respective lens units, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis, the slope (dx/da) of the focus cam, and the conversion coefficient .gamma..sub.a associated with the direction of rotation at the wide-angle end (F=36.0), the middle position (F=50.0), and the telephoto end (F=103.0), respectively. In these tables, (R) on the left side is the photographing distance (m), (ANG) is the amount of rotation on the focus cam upon focusing to the respective photographing distances, and 1), 2), 3), and 4) on the right side respectively represent the first, second, third, and fourth lens units. Also, in these tables, the first table summarizes the amount DX (mm) of movement for focusing in the direction of the optical axis upon focusing to the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m) (note that movement toward the object side is positive). The second table summarizes the imaging magnifications PK of the respective lens units in an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m). The third table summarizes the conversion coefficient .gamma..sub.x associated with the direction of the optical axis of the focusing lens unit in an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m). Furthermore, the fourth table summarizes the slope (dx/da) of the focus cam at the positions, on the focus cam, corresponding to an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m), and the fifth table summarizes the conversion coefficient .gamma..sub.a associated with the direction of rotation of the focusing lens unit in an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m).

As can be seen from Tables 3, 4, and 5, the conversion coefficient .gamma..sub.X associated with the direction of the optical axis and the slope (dx/da) of the focus cam at the respective focal lengths increase as the photographing distance becomes closer to the closest distance. Therefore, as can be seen from these tables, the conversion coefficient .gamma..sub.a associated with the direction of rotation, which is defined as the product of .gamma..sub.x and (dx/da), further increases.

More specifically, in a zoom lens in which the conversion coefficient .gamma..sub.X associated with the amount x of movement, in the direction of the optical axis, of the focusing lens unit in a closest in-focus state is larger than that in an infinity in-focus state, i.e., which satisfies:

when the focus cam which satisfies the following inequality, i.e., the focus cam has a shape having a larger slope (dx/da) at the closest corresponding position than that at the infinity corresponding position:

the following inequality is satisfied:

The rate of change, from the infinity in-focus value (.gamma..sub.aO) to the closest in-focus value (.gamma..sub.aR), of the conversion coefficient .gamma..sub.a associated with the angle a of rotation of the rotatable lens barrel undesirably becomes larger than the rate of change, from the infinity in-focus value (.gamma..sub.xO) to the closest in-focus value (.gamma..sub.xR), of the conversion coefficient .gamma..sub.x associated with the amount x of movement in the direction of the optical axis.

From Tables 3, 4, and 5 above, the rate of change of .gamma..sub.a is .times.5.43 at the wide-angle end (F=36.0), .times.6.26 at the middle position (F=50.0), and .times.4.36 at the telephoto-end (F=103.0).

As described above, when the conversion coefficient .gamma. changes in correspondence with the lens arrangement (e.g., focusing), as described in Japanese Patent Application Laid-Open No. 3-228006, a plurality of pairs of data of the conversion coefficient .gamma. and the correction coefficient .gamma. must be stored in the storage means in units of a plurality of divided focus ranges. Therefore, when the rate of change of .gamma..sub.a is large (.gamma..sub.aR /.gamma..sub.aO >>1.0), the number of divisions increases, and the storage capacity inevitably becomes large, resulting in an increase in cost. For example, when a change in .gamma..sub.a in a single focus range is divided under the condition defined by the following inequality:

the number N of divisions is expressed by inequality (a) below:

Therefore, the numbers N.sub.W, N.sub.M, and N.sub.T of divisions at the wide-angle end, middle position, and telephoto end have large values as follows:

The formula K=.gamma.(1+.gamma...DELTA.Bf) presented by Japanese Patent Application Laid-Open No. 62-170924 is rewritten to the conversion coefficient K.sub.a associated with the angle a of rotation of the rotatable lens barrel:

Then, the following formula is defined by using a correction coefficient .mu. (.gamma.=-1/.mu.):

Tables 6, 7, and 8 below summarize the calculation results of the values of the conversion coefficient K.sub.a and the correction coefficient .mu. according to the embodiment of Japanese Patent Application Laid-Open No. 5-142475 at the wide-angle end (F=36.0), middle position (F=50.0), and telephoto end (F=103.0) using the above formula.

In these tables, (R) is the object distance (m), (ANG) is the amount of rotation for focusing from the infinity corresponding position on the focus cam, (r) is the conversion coefficient .gamma..sub.a in the direction of rotation, (rs) is the conversion coefficient K.sub.a, (bf) is the defocus amount (mm), and (l) is the correction coefficient .mu.. Each table has a matrix structure, and eight rows in the vertical direction indicated by (POS) represent the object positions (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 mm), and four pairs (R, ANGLE) in the horizontal direction represent the lens arrangements of the focusing lens unit.

More specifically, the position of the focusing lens in the first pair in the upper two tables in each of Tables 6, 7, and 8, i.e., in the third and fourth columns is (R, ANGLE)=(0.0, 0.0), and it indicates that this position corresponds to the infinity corresponding position. Therefore, the third column (r) in the first table represents the value of the conversion coefficient .gamma..sub.a in the direction of rotation when the focusing lens unit is focused on an infinity object, and the fourth column (rs) represents the value of the conversion coefficient K.sub.a when the focusing lens unit is moved from an in-focus state on an infinity object to an in-focus state at the object distance in the second column. Furthermore, the third column (bf) in the second table represents the defocus amount ABf from a predetermined imaging position when the position of the focusing lens unit corresponds to the infinity corresponding position, and the object is located at an object distance in the second column, and the fourth column (l) represents the value of the correction coefficient .mu. when the focusing lens unit is moved from an in-focus state on an infinity object to an in-focus state at the object distance in the second column.

Similarly, the position of the focusing lens in the fourth pair in the lower two tables in each of Tables 6, 7, and 8, i.e., in the ninth and 10th columns is (R, ANGLE)=(0.85, 10.0), and it indicates that this position corresponds to the closest in-focus (R=0.85 m) corresponding position. Therefore, the ninth column (r) in the third table represents the value of the conversion coefficient .gamma..sub.a in the direction of rotation when the focusing lens unit is focused on a closest distance (R=0.85 m) object, and the 10th column (rs) represents the value of the conversion coefficient K.sub.a when the focusing lens unit is moved from an in-focus state on the closest distance (R=0.85 m) object to an in-focus state at the object distance in the second column. Furthermore, the ninth column (bf) in the fourth table represents the defocus amount .DELTA.Bf from a predetermined imaging position when the position of the focusing lens unit corresponds to the closest corresponding position, and the object is located at an object distance in the second column, and the 10th column (l) represents the value of the correction coefficient .mu. when the focusing lens unit is moved from an in-focus state on the closest distance (R=0.85 m) object to an in-focus state at the object distance in the second column.

From the above formulas, since the conversion coefficient in the direction of rotation is calculated by K.sub.a =.DELTA.Bf/.DELTA.a (where .DELTA.a: the amount of rotation for focusing), and the correction coefficient .mu. is calculated by .mu.=.DELTA.Bf/(1-K.sub.a /.gamma..sub.a), the value of the conversion coefficient K.sub.a (eighth row, fourth column in first table: 0.175) when the focusing lens unit is moved from an in-focus state on the infinity object to an in-focus state at the object distance (R=0.85 m) in Table 6 is calculated by K.sub.a =1.75/10.0=0.175 using .DELTA.Bf=1.75 and .DELTA.a=10.0. On the other hand, the value of the correction coefficient .mu. (eighth row, fourth column in second table: -1.00) is calculated as .mu.=-1.00 using .DELTA.Bf=1.75, K.sub.a =0.175, and .gamma..sub.a =0.064.

As can be seen from Tables 6, 7, and 8 above, when a change in conversion coefficient K.sub.a : (rs) (e.g., the fourth column in the first table) and a change in correction coefficient .mu.: (l) (e.g., the fourth column in the second table) at a given lens arrangement (e.g., at the infinity in-focus arrangement) are considered, the conversion coefficient K.sub.a and the correction coefficient .mu. considerably change depending on the object positions. In particular, the conversion coefficient K.sub.a has a larger value at the closest object side than that at the infinity object side. Since the conversion coefficient K.sub.a in the direction of rotation is defined by K.sub.a =.DELTA.Bf/.DELTA.a, the amount .DELTA.a of rotation for focusing at the infinity object side becomes larger than that at the closest object side relative to the defocus amount .DELTA.Bf.

The calculation results of the rate of change of K.sub.a with respect to .gamma..sub.a at the infinity in-focus arrangement and the closest in-focus arrangement at the wide-angle end (F=36.0), middle position (F=50.0), and telephoto end (F=103.0) in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 are as follows.

As described above, in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, since the change in conversion coefficient K.sub.a is large, the contribution of the correction term (.DELTA.Bf/.mu.) in K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) becomes large, and the value of the correction coefficient .mu. becomes close to that of the defocus amount .DELTA.Bf. In addition, the value of the correction coefficient .mu. largely changes depending on the object positions.

Therefore, as described in Japanese Patent Application Laid-Open No. 3-228006, under the condition that only a pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a given lens arrangement range (e.g., an infinity in-focus arrangement range), if the correction coefficient .mu. which changes largely is represented by only one value, a large error is included in the value of the conversion coefficient K.sub.a which is calculated from the conversion coefficient .gamma..sub.a and the correction coefficient .mu.. Therefore, when the lens driving amount .DELTA.a for focusing is finally calculated from the defocus amount .DELTA.Bf using the conversion coefficient K.sub.a, the lens driving amount includes an error, and an auto-focus operation cannot be accurately performed.

For example, upon calculation of the lens driving amount .DELTA.a for focusing with respect to a closest distance (R=0.85 m) object when the correction coefficient .mu. (which changes from -3.76 to -5.77 depending on the object distances) at the infinity in-focus arrangement at the telephoto end (F=103.0) is represented by the value (.mu.=-4.82) at the middle object distance (R=2.0 m), the lens driving amount .DELTA.a for focusing is calculated as .DELTA.a=8.74 by substituting .DELTA.Bf=16.18, .gamma..sub.a =0.425, and .mu.=-4.82. The actual lens driving amount for focusing from the state of the infinity in-focus arrangement at the telephoto end (F=103.0) to the closest distance (R=0.85 m) object is .DELTA.a=10.0 from (R, ANGLE)=(0.85, 10.0) in the upper right portion of the third table in Table 8. Therefore, an error as large as -12.6% is produced between the actual value and the calculated value .DELTA.a=8.74 of the lens driving amount for focusing.

Similarly, when the lens driving amounts upon focusing from the infinity in focus lens arrangement to the closest distance object and upon focusing from the closest in-focus lens arrangement to the infinity object at the wide-angle end, middle position, and telephoto end are calculated from .DELTA.a=.DELTA.Bf/›.gamma..sub.a (1-.DELTA.Bf/.mu.)!, and errors from the actual lens driving amounts are then calculated, the following large values are obtained.

Note that the value of the correction coefficient .mu. upon focusing from the infinity in-focus lens arrangement to the closest distance object adopts a value at the object distance (R=2.0 m), and the value of the correction coefficient .mu. upon focusing from the closest in-focus lens arrangement to the infinity object adopts a value at the object distance (R=3.0 m).

Finally, Table 9 summarizes the amount (ANGLE DA) of rotation for focusing upon manual focusing using the focus cam (the middle table in Table 1) of the embodiment of Japanese Patent Application Laid-Open No. 5-142475, the amount DX (mm) of movement, in the direction of the optical axis, of the focusing lens unit corresponding to the amount of rotation for focusing, and a displacement amount Bf (mm) of the imaging point when the amount (DX) of movement in the direction of the optical axis is given.

The upper table in Table 9 summarizes the displacement amount (Bf) of the imaging point corresponding to the photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.85 m) in the respective zooming states of the focal lengths (F=36.0, 50.0, 60.0, 70.0, 85.0, and 103.0 mm), and the middle table summarizes the values of the amount (ANGLE DA) of rotation for focusing required for attaining an optimal in-focus state with respect to the respective photographing distances. The lower table summarizes the amounts (DX) of movement, in the direction of the optical axis, of the respective lens units corresponding to the amount (ANGLE DA) of rotation for focusing in association with the focal lengths and the photographing distances. In the lower table, (F) is the focal length (mm) of the entire system, (R) is the photographing distance (m), and (DX) is the amount (mm) of movement, in the direction of the optical axis, of each of the first, second, third, and fourth lens units in turn from the right side (movement toward the object side is represented by a positive value).

It is, therefore, an object of the present invention to provide a zoom lens which can suppress changes in conversion coefficient .gamma..sub.a and correction coefficient .mu. above even when the focus cam is used for achieving manual focusing, can suppress the storage capacity by reducing the number of data of the conversion coefficient .gamma..sub.a and correction coefficient .mu. to be stored in the storage means, can eliminate an error upon calculation of the lens driving amount .DELTA.a for focusing from the defocus amount .DELTA.Bf using the conversion coefficient K.sub.a and can achieve accurate auto-focusing.

According to the present invention, in a zoom lens system in which the movement locus of a focusing lens unit is defined by synthesizing a focus cam and a zoom compensation cam so as to achieve an in-focus state by a substantially constant amount of rotation for an identical object distance independently of a zooming state upon expression of a predetermined movement locus for zooming by the amount of movement, in the direction of the optical axis, of lens units, and the angle of rotation of a rotatable lens barrel, when the ratios (dBf/dx) of the amount dBf of infinitesimal movement of the imaging plane to the amount dx of infinitesimal movement, in the direction of the optical axis, of the focusing lens unit at the infinity and closest in-focus points are respectively represented by .gamma..sub.XO and .gamma..sub.XR, the amounts of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end and the telephoto end are respectively represented by .DELTA.X.sub.WR and .DELTA.x.sub.TR and the amount of rotation of the focusing lens unit on the focus cam corresponding to zooming from the wide-angle end to the telephoto end and the amount of rotation corresponding to focusing from the infinity in-focus state to the closest in-focus state are respectively represented by a.sub.Z and a.sub.F, the zoom lens satisfies conditional formulas (1), (2), and (3) below at least at the telephoto end:

On the other hand, when the ratios (dBf/da) of the amount dBf of infinitesimal movement of the imaging plane with respect to the angle da of infinitesimal rotation of the focusing lens unit on the focus cam at the infinity and closest in-focus points are respectively represented by .gamma..sub.aO and .gamma..sub.aR, the zoom lens satisfies the following formula at least at the wide-angle end and the telephoto end:

Furthermore, when the conversion coefficients K.sub.a, which are used when the focusing lens unit are located at the lens arrangements corresponding to the infinity and closest in-focus states and are expressed by K.sub.a =.DELTA.Bf/.DELTA.a, are respectively represented by K.sub.aO and K.sub.aR, the zoom lens satisfies the following formulas at least at the wide-angle end and the telephoto end:

where

.DELTA.Bf: the defocus amount between the imaging position of an object at an arbitrary position and a predetermined imaging point position

.DELTA.a: the angle of rotation of the focusing lens unit on the focus cam required for attaining an in-focus state on the object

As in the above-mentioned first aspect of the present invention, in the third aspect of the present invention, since the above-mentioned conditional formulas are satisfied, even when the focus cam is used to achieve so-called manual focusing, changes in conversion coefficient .gamma..sub.a and correction coefficient .mu. required for realizing accurate auto-focusing can be reduced. For this reason, the number of data of the conversion coefficient .gamma..sub.a and correction coefficient .mu. to be stored in the storage means can be reduced. Furthermore, since the change in correction coefficient .mu. is small, an error upon calculation of the lens driving amount .DELTA.a for focusing from the defocus amount .DELTA.Bf using the conversion coefficient K.sub.a is small, and accurate auto-focusing can be realized.

As described above, when the zoom lens system is constituted by n lens units, and its k-th lens unit is used as a focusing lens unit, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis of the focusing lens unit (the ratio dBf/dx of the amount dBf of infinitesimal movement of the imaging plane to the amount dx of infinitesimal movement in the direction of the optical axis) is expressed using the imaging magnifications .beta. of the respective lens units as follows:

Therefore, the rate of change, from the infinity in-focus value (.gamma..sub.xO) to the closest in-focus value (.gamma..sub.xR), of the conversion coefficient .gamma..sub.x associated with the direction of the optical axis can be expressed using the imaging magnifications .beta..sub.ok and .beta..sub.Rk of the focusing lens unit at the infinity and closest in-focus points as follows:

On the other hand, the conversion coefficient .gamma..sub.a associated with the direction of rotation of the focusing lens unit (the ratio dBf/da of the amount dBf of infinitesimal movement of the imaging plane to the angle da of infinitesimal rotation) can be expressed by:

where dx/da is the slope of the focus cam. For this reason, the rate of change, from the infinity in-focus value (.gamma..sub.aO) to the closest in-focus value (.gamma..sub.aR), of the conversion coefficient .gamma..sub.a associated with the direction of rotation of the focusing lens unit can be expressed using slopes (dx/da).sub.O and (dx/da).sub.R at the infinity and closest corresponding positions on the focus cam as follows:

Therefore, like in the present invention, in the zoom lens system in which the value of the conversion coefficient .gamma..sub.X associated with the amount x of movement, in the direction of the optical axis, of the focusing lens unit in the closest in-focus state becomes larger than that in the infinity in-focus state (1.0<.gamma..sub.xR /.gamma..sub.xO), the ratio of the amount a.sub.F of rotation of the focusing lens unit on the focus cam corresponding to focusing from the infinity in-focus state to the closest in-focus state and the amount a.sub.Z of rotation corresponding to zooming from the wide-angle end to the telephoto end is set to be negative (a.sub.F /a.sub.Z <0), so that the focus cam can have a shape in which the slope (dx/da) at the closest corresponding position becomes smaller than that at the infinity corresponding position (0<(dx/da).sub.R /(dx/da).sub.O <1.0), thereby reducing the change in conversion coefficient .gamma..sub.a associated with the direction of rotation.

More specifically, since the rate of change (.gamma..sub.aR /.gamma..sub.aO) from the infinity in-focus value (.gamma..sub.aO) to the closest in-focus value (.gamma..sub.aR), of the conversion coefficient .gamma..sub.a associated with the direction of rotation is expressed as a product of the rate of change (.gamma..sub.xR /.gamma..sub.xO) of the conversion ratio .gamma..sub.x associated with the direction of the optical axis and the slope ratio (dx/da).sub.R /(dx/da).sub.O of the focus cam, as described above, the final rate of change (.gamma..sub.aR /.gamma..sub.aO) of the conversion coefficient .gamma..sub.a associated with the direction of rotation can be compressed by adopting an arrangement in which the two changes cancel out each other.

According to the present invention, in a zoom lens in which the conversion coefficients .gamma..sub.x associated with the amount x of movement, in the direction of the optical axis, of the focusing lens unit at the infinity and closest in-focus points at the telephoto end satisfies conditional formula (1):

when the ratio between the amounts .DELTA.X.sub.WR and .DELTA.X.sub.TR of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end and the telephoto end satisfies conditional formula (2):

the ratio of the amount a.sub.F of rotation of the focusing lens unit on the focus cam corresponding to focusing from the infinity in-focus state to the closest in-focus state to the amount a.sub.z of rotation corresponding to zooming from the wide-angle end to the telephoto end is set to satisfy conditional formula (3):

Under these conditions, the final rate of change (.gamma..sub.aR /.gamma..sub.aO) of the conversion coefficient .gamma..sub.a associated with the direction of rotation can be set to be a small value which satisfies conditional formula (4) below:

As described above, since the change in conversion coefficient .gamma..sub.a can be reduced as compared to that in the conventional system, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means can be reduced.

For example, upon division of the focus range like in formula (a) (N>log(.gamma..sub.MAX /.gamma..sub.MIN)/log(1.2)) above, the following relation is satisfied:

and the number of divisions can be smaller than in the conventional system. Therefore, cost can be reduced in terms of the storage capacity. Furthermore, as will be described later in the following description of the embodiments, since the changes in conversion coefficient K.sub.a and correction coefficient .mu. are smaller than those in the conventional system, an error obtained upon calculation of the lens driving amount .DELTA.a for focusing from the defocus amount ABf using the conversion coefficient K.sub.a is small, and an accurate auto-focusing operation can be realized.

The conditional formulas of the present invention will be explained below.

Conditional formula (1) is associated with the focusing lens unit in the zoom lens according to the present invention. When .gamma..sub.xR /.gamma..sub.xO is smaller than the lower limit of conditional formula (1) (.gamma..sub.xR /.gamma..sub.xO <1.0), the conversion coefficient .gamma..sub.x associated with the direction of the optical axis in the closest in-focus state becomes smaller than that in the infinity in-focus state. For this reason, when the focus cam (0<(dx/da).sub.R /(dx/da).sub.O <1.0) according to the present invention is used, the rate of change of the conversion coefficient .gamma..sub.a associated with the direction of rotation, which rate is expressed as a product of the rate of change (.gamma..sub.xR /.gamma..sub.xO) of the conversion coefficient .gamma..sub.x associated with the direction of the optical axis and the slope ratio ((dx/da).sub.R /(dx/da).sub.O) of the focus cam, becomes excessively smaller than 1.0 (.gamma..sub.aR /.gamma..sub.aO >>1.0), and changes in .gamma..sub.a become large. As a result, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means increases. In addition, since the changes in conversion coefficient K.sub.a and correction coefficient .mu. become large, the error obtained upon calculation of the lens driving amount .DELTA.a from the defocus amount .DELTA.Bf is large, and an accurate auto-focusing operation cannot be performed.

Conditional formula (2) is associated with the ratio between the amounts of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide--angle end and the telephoto end. As will be described later in the description of the embodiments, this ratio is an amount which is associated with the ratio of the slope (dx/da).sub.R at the closest corresponding position to the slope (dx/da).sub.o at the infinity corresponding position on the focus cam. As the ratio between the two amounts of movement becomes smaller, changes in slope on the focus cam become smaller. On the contrary, as the ratio between the two amounts of movement becomes larger, changes in slope on the focus cam become larger. Therefore, when the ratio is smaller than the lower limit of conditional formula (2), changes in conversion coefficient .gamma..sub.a associated with the direction of rotation become small. However, in the zoom lens of the present invention, which satisfies conditional formula (1), the optimal ratio of the amount a.sub.F of rotation of the focusing lens unit on the focus cam corresponding to focusing from the infinity in-focus state to the closest in-focus state to the amount a.sub.Z of rotation corresponding to zooming from the wide-angle end to the telephoto end falls outside a range defined by conditional formula (3). Therefore, it is more preferable to set the upper limit of conditional formula (2) to 4.30. On the other hand, when the ratio exceeds the upper limit of conditional formula (2), since changes in slope on the focus cam become too large as compared to those in conversion coefficient .gamma..sub.x associated with the direction of the optical axis, changes in conversion coefficient .gamma..sub.a associated with the direction of rotation become large, and the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means increases. In addition, an accurate auto-focusing operation cannot be performed. Conditional formula (3) defines an appropriate ratio of the amount a.sub.F of rotation of the focusing lens unit on the focus cam corresponding to focusing from the infinity in-focus state to the closest in-focus state to the amount a.sub.Z of rotation corresponding to zooming from the wide-angle end to the telephoto end. When the ratio is smaller than the lower limit of conditional formula (3), the slope (dx/da) of the focus cam considerably decreases at the closest corresponding position as compared to the slope at the infinity corresponding position, and they have a ratio:

For this reason, the rate of change of the conversion coefficient .gamma..sub.a associated with the direction of rotation, which rate is expressed as a product of the rate of change (.gamma..sub.xR /.gamma..sub.xO) of the conversion coefficient .gamma..sub.x associated with the direction of the optical axis and the slope ratio ((dx/da).sub.R /(dx/da).sub.O) of the focus cam, becomes excessively smaller than 1.0 (.gamma..sub.aR /.gamma..sub.aO <<1.0), and changes in .gamma..sub.a become large. As a result, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means increases. In addition, since changes in .mu. are large, an error obtained upon calculation of the lens driving amount .DELTA.a from the defocus amount .DELTA.Bf is large, and an accurate auto-focusing operation cannot be performed. Therefore, it is more preferable to set the lower limit of conditional formula (3) to -0.68.

On the contrary, when the ratio exceeds the upper limit of conditional formula (3), since the rate of change (.gamma..sub.aR /.gamma..sub.aO) of the conversion coefficient .gamma..sub.a becomes closer to 1.0, changes in .gamma..sub.a become small, and the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means can be reduced. However, since the amount aF of rotation for focusing becomes small relative to the amount a.sub.z of rotation corresponding to zooming from the wide-angle end to the telephoto end, the amount of rotation for so-called manual focusing becomes small, and it becomes difficult to manually attain accurate focusing. Therefore, it is more preferable to set the lower limit of conditional formula (3) to -0.52.

Conditional formula (4) is a condition associated with the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means, i.e., the number of divisions of the focus range. When .gamma..sub.aR /.gamma..sub.aO is smaller than the lower limit of conditional formula (4), the rate of change (.gamma..sub.aR /.gamma..sub.aO) of the conversion coefficient .gamma..sub.a becomes excessively smaller than 1.0, and changes in .gamma..sub.a become large. As a result, since the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means increases, a storage means with a large storage capacity is required, resulting in an increase in cost.

On the contrary, when .gamma..sub.aR /.gamma..sub.aO exceeds the upper limit of conditional formula (4), since the rate of change (.gamma..sub.aR /.gamma..sub.aO) of the conversion coefficient .gamma..sub.a becomes closer to 1.0, changes in .gamma..sub.a become small, and the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. to be stored in the storage means can be reduced. However, since the conversion coefficient .gamma..sub.a must have a considerably large value, the sensitivity (dBf/da) associated with the movement in the direction of rotation becomes strict, and a change in imaging point caused by a slight error factor in the direction of rotation becomes large, thus disturbing accurate auto-focusing.

Furthermore, in order to attain accurate auto-focusing while lowering the sensitivity (dBf/da) associated with the movement in the direction of rotation, the upper and lower limits of conditional formula (4) are preferably set as follows:

In order to obtain a zoom lens which can perform auto-focusing more accurately, when the conversion coefficients K.sub.a (=.DELTA.Bf/.DELTA.a) used when the focusing lens unit is located at the lens arrangements corresponding to the infinity in-focus state and the closest in-focus state are respectively represented by K.sub.aO and K.sub.aR, the zoom lens preferably satisfies conditional formulas (5) and (6) below at least at the wide-angle end and the telephoto end:

Conditional formula (5) defines the rate of change of the conversion coefficient K.sub.a in the direction of rotation upon a change in object position when the focusing lens unit corresponds to an arrangement in the infinity in-focus state. When the rate is smaller than the lower limit of conditional formula (5), the change in conversion coefficient K.sub.aO upon a change in object position becomes too small as compared to the conversion coefficient .gamma..sub.aO as the sensitivity associated with the movement in the direction of rotation of the focusing lens unit at the infinity in-focus point. Therefore, for example, when the conversion coefficient K.sub.aO which changes upon a change in object position is expressed by a pair of a conversion coefficient .gamma..sub.aO value and a correction coefficient .mu..sub.aO value on the basis of the relationship K.sub.aO =.gamma..sub.aO (1-.DELTA.Bf/.mu..sub.aO), a large error is produced in the value of the conversion coefficient K.sub.aO calculated from the conversion coefficient .gamma..sub.aO and the correction coefficient .mu..sub.aO, thus disturbing accurate auto-focusing.

On the contrary, when the rate exceeds the upper limit of conditional formula (5), the change in conversion coefficient K.sub.aO in the direction of rotation upon a change in object position becomes large as compared to the conversion coefficient .gamma..sub.aO in the direction of rotation of the focusing lens unit at the infinity in-focus point. For this reason, when the conversion coefficient K.sub.aO which changes upon a change in object position is expressed by a pair of a conversion coefficient .gamma..sub.aO value and a correction coefficient .mu..sub.aO value, a large error is produced in the value of the conversion coefficient K.sub.aO calculated from the conversion coefficient and the correction coefficient .mu..sub.aO.

In order to achieve auto-focusing more accurately, the upper and lower limits of conditional formula (5) are preferably set as follows:

Similarly, when the conversion coefficient K.sub.aO changes from (K.sub.aO /.gamma..sub.aO <1) to (K.sub.aO /.gamma..sub.aO >1) upon a change in object position when the focusing lens unit corresponds to an arrangement in the infinity in-focus state, the sign of the correction coefficient Pao changes before and after (K.sub.aO /.gamma..sub.aO =1). As a result, when the conversion coefficient K.sub.ao is expressed by a pair of a conversion coefficient .gamma..sub.a0 value and a correction coefficient .mu..sub.a value, a large error is produced in the value of the conversion coefficient K.sub.aO calculated from the conversion coefficient .gamma..sub.aO and the correction coefficient .mu..sub.aO. Therefore, the conversion coefficient K.sub.aO does not preferably change too much after it exceeds (K.sub.aO /.gamma..sub.aO =1).

Therefore, even when the conversion coefficient K.sub.aO changes from (K.sub.aO /.gamma..sub.aO <1) to (K.sub.aO /.gamma..sub.aO >1), the zoom lens preferably satisfies the following conditional formula:

Conditional formula (6) defines the rate of change of the conversion coefficient K.sub.a in the direction of rotation upon a change in object position when the focusing lens unit corresponds to an arrangement in the closest in-focus position. When the rate exceeds the upper limit of conditional formula (6), the change in conversion coefficient K.sub.aR in the direction of rotation upon a change in object position becomes too large as compared to the conversion coefficient .gamma..sub.aR as the sensitivity associated with the movement in the direction of rotation of the focusing lens unit at the closest in-focus point. Therefore, for example, when the conversion coefficient K.sub.aR which changes upon a change in object position is expressed by a pair of a conversion coefficient .gamma..sub.aR value and a correction coefficient .mu..sub.aR value on the basis of the relationship K.sub.aR =.gamma..sub.aR (1-.DELTA.Bf/.mu..sub.aR), a large error is produced in the value of the conversion coefficient KaR calculated from the conversion coefficient .gamma..sub.aR and the correction coefficient .mu..sub.aR thus disturbing accurate auto-focusing.

On the contrary, when the rate is smaller than the lower limit of conditional formula (6), the change in conversion coefficient K.sub.aR in the direction of rotation upon a change in object position becomes small as compared to the conversion coefficient .gamma..sub.aR in the direction of rotation of the focusing lens unit at the closest in-focus point. For this reason, when the conversion coefficient K.sub.aR which changes upon a change in object position is expressed by a pair of a conversion coefficient .gamma..sub.aR value and a correction coefficient .mu..sub.aR value, a large error is produced in the value of the conversion coefficient K.sub.aR calculated from the conversion coefficient .gamma..sub.aR and the correction coefficient .mu..sub.aR.

In order to achieve auto-focusing more accurately, the upper and lower limits of conditional formula (6) are preferably set as follows:

Similarly, when the conversion coefficient K.sub.aR changes from (K.sub.aR /.gamma..sub.aR <1) to (K.sub.aR /.gamma..sub.aR >1) upon a change in object position when the focusing lens unit corresponds to an arrangement in the closest in-focus state, the sign of the correction coefficient .mu..sub.aR changes before and after (K.sub.aR /.gamma..sub.aR =1). As a result, when the conversion coefficient K.sub.aR is expressed by a pair of a conversion coefficient .gamma..sub.aR value and a correction coefficient .mu..sub.aR value, a large error is produced in the value of the conversion coefficient K.sub.aR calculated from the conversion coefficient .gamma..sub.aR and the correction coefficient .mu..sub.aR. Therefore, the conversion coefficient K.sub.aR preferably does not change too much after it exceeds (K.sub.aR /.gamma..sub.aR =1).

Therefore, even when the conversion coefficient K.sub.aR changes from (K.sub.aR /.gamma..sub.aR <1) to (K.sub.aR /.gamma..sub.aR >1), the zoom lens preferably satisfies the following conditional formula:

The above and other objects, features and advantages of the present invention are explained hereinafter and may be better understood by reference to the drawings and the descriptive matter which follows.

FIG. 1A is a view showing the movement loci for zooming of a zoom lens according to the first embodiment of the present invention;

FIG. 1B is a view showing the shapes of a focus cam and a zoom compensation cam of a second lens unit in the zoom lens according to the first embodiment of the present invention; and

FIG. 2 is a view for explaining the shape of the focus cam in the zoom lens according to the first embodiment of the present invention.

The present invention will be described in detail hereinafter with reference to its embodiments.

A zoom lens of the first embodiment is a zoom lens which has a four-unit arrangement, i.e., positive, negative, positive, and positive lens units, and attains focusing by a negative second lens unit. In this zoom lens, the rotation amount ratio (a.sub.F /a.sub.Z) of the rotation amount for focusing from the infinity in-focus position to the closest in-focus position (R=0.8 m) to the amount of rotation for zooming from the wide-angle end (F=36.0) to the telephoto end (F=131.0) is set to be -0.55.

Table 10 below summarizes various paraxial data of an optical system and data for defining the shape of a focus cam according to the first embodiment.

The upper table in Table 10 summarizes the focal length data, and the principal point interval data relating to six zooming states (F=36.0 (1-POS), 50.0 (2-POS), 70.0 (3-POS), 85.0 (4-POS), 105.0 (5-POS), and 131.0 mm (6-POS)) of the respective lens units of the optical system corresponding to the first embodiment.

In this table, F1, F2, F3, and F4 are respectively the focal lengths of first, second, third and fourth lens units, and D1, D2, D3, and D4 are respectively the principal point interval between the first and second lens units, the principal point interval between the second and third lens units, the principal point interval between the third and fourth lens units, and the principal point interval between the fourth lens unit and a predetermined imaging plane in six zooming states (F=36.0, 50.0, 70.0, 85.0, 105.0 and 131.0 mm).

The middle table in Table 10 summarizes spline sample data when the shape (a curve g.sub.2F in FIG. 1B) of the focus cam in the second lens unit of the first embodiment, which is used for focusing, is expressed by the above-mentioned spline function associated with the angle a of rotation of a rotatable lens barrel and the amount x of movement in the direction of the optical axis. In this middle table, (1), (2), (3), and (4) correspond to the first, second, third, and fourth lens units, respectively.

Furthermore, the lower table in Table 10 summarizes the infinity focusing positions (infinity corresponding positions) at the respective focal lengths (F=36.0, 50.0, 70.0, 85.0, 105.0 and 131.0 mm), and the amounts of rotation (amounts of rotation for focusing) upon focusing to respective photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.8 m) using the focus cam of the first embodiment. In the lower table in Table 10, since the amount of rotation for zooming from the wide-angle end (F=36.0) to the telephoto end (F=131.0) is set to be 10.0, and the amount of rotation for focusing from the infinity in-focus position to the closest in-focus position (R=0.8 m) is set to be -5.5, the rotation amount ratio (a.sub.F /a.sub.Z) of the amount of rotation for focusing to the amount of rotation for zooming in the first embodiment is

Table 11 below summarizes the numerical value data of the cams of the focusing lens unit in the first embodiment, which data are calculated by interpolation based on a spline function on the basis of the sample data of the focus cam summarized in the middle table in Table 10. In this table, (ANGLE) is the angle of rotation of the rotatable lens barrel, (2) is the amount (mm) of movement, in the direction of the optical axis, of the second lens unit, and (F) is the focal length (mm) of the entire system in an infinity in-focus state corresponding to the amount (ANGLE) of rotation.

The left table in Table 11 summarizes the numerical value data of the focus cam of the first embodiment, and the right table in Table 11 summarizes the numerical value data of the zoom compensation cam of this embodiment. A value obtained by synthesizing the amounts (2) of movement in the direction of the optical axis in the numerical value data of the focus cam and the zoom compensation cam in the range from the amount of rotation (ANGLE=0.0) to the amount of rotation (ANGLE=10.0) coincides with the movement locus (a curve g.sub.2 in FIG. 1A) of the second lens unit calculated using the paraxial data in the upper table in Table 10.

Therefore, the zoom compensation cam (a curve g.sub.2H in FIG. 1B) is determined by subtracting the focus cam (the curve g.sub.2F in FIG. 1B) from the movement locus (the curve g.sub.2 in FIG. 1A) upon zooming of the second lens unit determined by the paraxial data in the upper table in Table 10.

FIGS. 1A and 1B and FIG. 2 will be briefly described below.

FIG. 1A shows the paraxial arrangement and the movement loci upon zooming of the zoom lens according to the first embodiment, and FIG. 1B shows the shapes of the focus cam and the zoom compensation cam of the second lens unit of this embodiment. Referring to FIGS. 1A and 1B, G1, G2, G3, and G4 respectively represent the first, second, third, and fourth lens units, and g.sub.1, g.sub.2, g.sub.3, and g.sub.4 respectively represent the movement loci upon zooming of the first, second, third, and fourth lens units. In addition, g.sub.2F, and g.sub.2H respectively represent the shapes of the focus cam and the zoom compensation cam of the second lens unit. As described above, a shape obtained by synthesizing the focus cam g.sub.2F and the zoom compensation cam g.sub.2H of the second lens unit coincides with the movement locus g.sub.2 of the second lens unit.

FIG. 2 is a view for explaining the shape of the focus cam g.sub.2F of the first embodiment. Referring to FIG. 2, (f=36.0; R=un) and (f=36.0; R=0.80) respectively represent the in-focus positions at the infinity and the closest distance (R=0.80 m) at the wide-angle end, and coordinate positions (x; a) on the focus cam are respectively (x; a)=(0; 0) and (x; a)=(1.041; -5.5). On the other hand, (f=131; R=un) and (f=131; R=0.80) respectively represent the in-focus positions at the infinity and the closest distance (R=0.80 m) at the telephoto end, and coordinate positions (x; a) on the focus cam are respectively (x; a)=(-7.200; 10) and (x; a)=(-1.524; 4.5).

Upon zooming from the wide-angle end to the telephoto end, the second lens unit moves on the focus cam g.sub.2F from the coordinate position (0; 0) to the coordinate position (-7.200; 10) for an infinity object, and from the coordinate position (1.041; -5.5) to the coordinate position (-1.524; 4.5) for a closest distance object. Therefore, the second lens unit moves by 10.0 in the direction of rotation (the direction of an axis a) in both the cases. On the other hand, upon focusing from the infinity arrangement to the closest distance object, the second lens unit moves on the focus cam g.sub.2F from the coordinate position (0; 0) to the coordinate position (1.041; -5.5) at the wide-angle end, and from the coordinate position (-7.200; 10) to the coordinate position (-1.524; 4.5) at the telephoto end. Therefore, the second lens unit moves by -5.5 in the direction of rotation (the direction of the axis a) at these ends. In contrast to this, in the direction of the optical axis (the direction of an axis x), the second lens unit moves by 1.041 at the wide-angle end, and by 5.676 at the telephoto end.

Since the shape of the focus cam g.sub.2F is determined by interpolating the coordinates (f=36.0; R=0.80), (f=36.0; R=un), (f=131; R=0.80), and (f=131; R=un) by the spline function, the change in slope (dx/da) of the focus cam g.sub.2F becomes larger as the absolute value of the x-coordinate of (f=36.0; R=0.80) is smaller or as the absolute value of the x-coordinate of (f=131; R=un) is larger. More specifically, as the ratio (.DELTA.x.sub.TR /.DELTA.X.sub.WR) between the amounts .DELTA.xTR and .DELTA.XWR of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end or telephoto end is larger, the change in slope (dx/da) of the focus cam becomes larger.

Tables 12, 13, and 14 below summarize the amount DX (mm) of movement for focusing, in the direction of the optical axis, of the focusing lens unit, the imaging magnifications .beta..sub.k , of the respective lens units, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis, the slope (dx/da) of the focus cam, and the conversion coefficient .gamma..sub.a associated with the direction of rotation at the wide-angle end (F=36.0), the middle position (F=70.0), and the telephoto end (F=131.0) according to the first embodiment, respectively. In these tables, (R) on the left side is the photographing distance (m), (ANG) is the amount of rotation on the focus cam upon focusing to the respective photographing distances, and 1), 2), 3), and 4) on the right side respectively represent the first, second, third, and fourth lens units. Also, in these tables, the first table summarizes the amount DX (mm) of movement for focusing in the direction of the optical axis upon focusing to the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m) (note that movement toward the object side is positive). The second table summarizes the imaging magnifications .beta..sub.k of the respective lens units in an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m). The third table summarizes the conversion coefficient .gamma..sub.x associated with the direction of the optical axis of the focusing lens unit in an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m). Furthermore, the fourth table summarizes the slope (dx/da) of the focus cam at the positions, on the focus cam, corresponding to an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m), and the fifth table summarizes the conversion coefficient .gamma..sub.a associated with the direction of rotation of the focusing lens unit in an in-focus state at the respective photographing distances (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m).

As can be seen from Tables 12, 13, and 14, at each focal length, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis increases but the value of the slope (dx/da) of the focus cam decreases as the photographing distance becomes closer to the closest distance. Therefore, as can be seen from these tables, the value of the conversion coefficient .gamma..sub.a associated with the direction of rotation, which is defined as the product of the conversion coefficient .gamma..sub.x and the slope (dx/da) of the focus cam, decreases as the photographing distance becomes closer to the closest distance by the influence of the slope (dx/da) of the focus cam, contrary to the embodiment of Japanese Patent Application Laid-Open No. 5-142475.

As described above, when the ratio (.DELTA.x.sub.TR /.DELTA.X.sub.WR) between the amounts .DELTA.x.sub.TR and .DELTA.X.sub.WR of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end and the telephoto end is large, the degree of the decrease in slope (dx/da) of the focus cam also becomes large. For this reason, the conversion coefficient .gamma..sub.a associated with the direction of rotation further decreases under the influence of the slope (dx/da) of the focus cam as the photographing distance becomes closer to the closest distance.

From Tables 12, 13, and 14, the rate of change, from the infinity in-focus position to the closest in-focus position, of the conversion coefficient .gamma..sub.a associated with the direction of rotation is .times.0.59 at the wide-angle end (F=36.0), .times.0.50 at the middle position (F=70.0), and .times.0.31 at the telephoto end (F=131.0). When the number N of divisions of the focus range upon a change in conversion coefficient .gamma..sub.a in the first embodiment is calculated using formula (a), and is compared with that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, the numbers N.sub.W, N.sub.M, and N.sub.T of divisions at the wide-angle end, middle position, and telephoto end respectively have the following values:

Embodiment of Japanese Patent Application Laid-Open No. 5-142475

First Embodiment

Therefore, as can be understood from a comparison with the previously calculated values in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, although the ratio (.DELTA.x.sub.TR /.DELTA.x.sub.WR) between the amounts .DELTA.X.sub.TR and .DELTA.x.sub.WR of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end and the telephoto end in the first embodiment is larger than that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 (the embodiment of Japanese Patent Application Laid-Open No. 5-142475: 3.94; the first embodiment: 5.45), the values of the numbers N of divisions become small conversely.

As described above, in the zoom lens of the first embodiment, since the rate of change, from the infinity in-focus position to the closest in-focus position, of the conversion coefficient .gamma..sub.a associated with the direction of rotation becomes much smaller than that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. can be reduced, and the storage capacity can be suppressed.

Tables 15, 16, and 17 summarize the calculation results of the conversion coefficient K.sub.a and the correction coefficient .mu. at the wide-angle end (F=36.0), middle position (F=70.0), and telephoto end (F=131.0) according to the first embodiment. In these tables, (R) is the object distance (m), (ANG) is the amount of rotation for focusing from the infinity corresponding position on the focus cam, (r) is the conversion coefficient .gamma..sub.a in the direction of rotation, (rs) is the conversion coefficient K.sub.a, (bf) is the defocus amount (mm), and (l) is the correction coefficient .mu.. Each table has a matrix structure, and eight rows in the vertical direction indicated by (POS) represent the object positions (R=10.0, 5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 mm), and four pairs (R, ANGLE) in the horizontal direction represent the lens arrangements of the focusing lens unit.

More specifically, the position of the focusing lens in the first pair in the upper two tables in each of Tables 15, 16, and 17, i.e., in the third and fourth columns is (R, ANGLE)=(0.0, 0.0), and it indicates that this position corresponds to the infinity corresponding position. Therefore, the third column (r) in the first table represents the value of the conversion coefficient .gamma..sub.a in the direction of rotation when the focusing lens unit is focused on an infinity object, and the fourth column (rs) represents the value of the conversion coefficient K.sub.a when the focusing lens unit is moved from an in-focus state on an infinity object to an in-focus state at the object distance in the second column. Furthermore, the third column (bf) in the second table represents the defocus amount .DELTA.Bf from a predetermined imaging position when the position of the focusing lens unit corresponds to the infinity corresponding position, and an object is located at an object distance in the second column, and the fourth column (l) represents the value of the correction coefficient .mu. when the focusing lens unit is moved from an in-focus state on an infinity object to an in-focus state at the object distance in the second column.

Similarly, the position of the focusing lens in the fourth pair in the lower two tables in each of Tables 15, 16, and 17, i.e., in the ninth and tenth columns is (R, ANGLE)=(0.8, -5.5), and it indicates that this position corresponds to the closest in-focus (R=0.8 m) corresponding position. Therefore, the ninth column (r) in the third table represents the value of the conversion coefficient .gamma..sub.a in the direction of rotation when the focusing lens unit is focused on a closest distance (R=0.80 m) object, and the tenth column (rs) represents the value of the conversion coefficient K.sub.a when the focusing lens unit is moved from an in-focus state on the closest distance (R=0.80 m) object to an in-focus state at the object distance in the second column. Furthermore, the ninth column (bf) in the fourth table represents the defocus amount .DELTA.Bf from a predetermined imaging position when the position of the focusing lens unit corresponds to the closest corresponding position, and the object is located at an object distance in the second column, and the tenth column (l) represents the value of the correction coefficient .mu. when the focusing lens unit is moved from an in-focus state on the closest distance (R=0.80 m) object to an in-focus state at the object distance in the second column.

As described above, since the conversion coefficient in the direction of rotation is calculated by K.sub.a =.DELTA.Bf/.DELTA.a (where .DELTA.a: the amount of rotation for focusing), and the correction coefficient .mu. is calculated by .mu.=.DELTA.Bf/(1 -K.sub.a /.gamma..sub.a), the value of the conversion coefficient K.sub.a (eighth row, fourth column in first table: -0.336) when the focusing lens unit is moved from an in-focus state on the infinity object to an in-focus state at the object distance (R=0.80 m) in Table 15 is calculated by K.sub.a =1.85/-5.5=-0.336 using .DELTA.Bf=1.85 and .DELTA.a=-5.5. On the other hand, the value of the correction coefficient .mu. (eighth row, fourth column in second table: 10.77) is calculated as .mu.=10.77 using .DELTA.Bf=1.85, K.sub.a =-0.336, and .gamma..sub.a

As can be seen from Tables 15, 16, and 17 above, when a change in conversion coefficient K.sub.a : (rs) (e.g., the fourth column in the first table) at a given lens arrangement (e.g., at the infinity in-focus arrangement) is considered, the rate of change becomes small as compared to the change in K.sub.a (Tables 6, 7, and 8) in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 examined previously.

More specifically, the amount Aa of rotation for focusing in the first embodiment at the infinity object side becomes relatively smaller than that at the closest object side, as compared to Japanese Patent Application Laid-Open No. 5-142475. In fact, when the ratio between the amount of rotation for focusing upon focusing to the closest distance and the amount of rotation for focusing upon focusing to the object distance (R=5.0 m) is calculated in Tables 1 and 10, 3.379/10.0=0.338 in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, while -0.665/-5.5=0.121 in the first embodiment. As described above, when the focus cam with the arrangement of the present invention is used, since the amount .DELTA.a of rotation for focusing becomes relatively smaller at the infinity object side, the conversion coefficient K.sub.a becomes relatively large at the infinity object side, and consequently, the change in conversion coefficient K.sub.a in the direction of rotation can be reduced as compared to the conventional system.

The calculation results of the rate of change of K.sub.a with respect to .gamma..sub.a at the infinity in-focus arrangement and the closest in-focus arrangement at the wide-angle end, middle position, and telephoto end in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and in the first embodiment of the present invention are as follows.

As described above, according to the present invention, since the rate of change of K.sub.a with respect to .gamma..sub.a is small as compared to the conventional system, and the contribution of the correction term (.DELTA.Bf/.mu.) in K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) can be reduced, the value of the correction coefficient p can be set to be large as compared to the defocus amount .DELTA.Bf, and at the same time, the change in correction coefficient .mu. can be decreased.

Therefore, even when only a pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a given lens arrangement range, an error in the conversion coefficient K.sub.a calculated using .gamma..sub.a and .mu. or in the actual lens driving amount .DELTA..sub.a for focusing can be eliminated.

Next, in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and the first embodiment of the present invention, when the lens driving amounts upon focusing from the infinity in-focus lens arrangement to the closest distance object and upon focusing from the closest in-focus lens arrangement to the infinity object at the wide-angle end, middle position, and telephoto end are calculated from .DELTA.a=.DELTA.Bf/›.gamma..sub.a (1-.DELTA.Bf/.mu.)!, and errors from the actual lens driving amounts are then calculated, the following values are obtained. Note that the value of the correction coefficient .mu. upon focusing from the infinity in-focus lens arrangement to the closest distance object adopts a value at the object distance (POS-6), and the value of the correction coefficient .mu. upon focusing from the closest in-focus lens arrangement to the infinity object adopts a value at the object distance (POS-4).

As described above, even when only a pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a given lens arrangement range, an error between the conversion coefficient K.sub.a calculated from .gamma..sub.a and .mu. and the lens driving amount .DELTA.a for focusing becomes small as compared to the conventional system, and focusing can be realized with higher accuracy.

For the sake of reference, when errors of the lens driving amounts upon focusing from the infinity in-focus lens arrangement to the object distance (R=10.0 m) and upon focusing from the closest in-focus lens arrangement to the object distance (R=1.0 m) are calculated and compared, the following results are obtained. As can be seen from these tables, focusing accuracy can be relatively improved independently of the object distance.

Next, an examination will be made as to whether not only accurate auto-focusing but also so-called manual focusing can be attained in the zoom lens of the first embodiment.

Table 18 summarizes the amount (ANGLE DA) of rotation for focusing upon manual focusing using the focus cam (the middle table in Table 10) of the first embodiment, the amount DX (mm) of movement, in the direction of the optical axis, of the focusing lens unit corresponding to the amount of rotation for focusing, and the displacement amount Bf (mm) of the imaging point when the amount (DX) of movement in the direction of the optical axis is given.

The upper table in Table 18 summarizes the displacement amount (Bf) of the imaging point corresponding to the photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m) in the respective zooming states of the focal lengths (F=36.0, 50.0, 70.0, 85.0, 105.0, and 131.0 mm), and the middle table summarizes the values of the amount (ANGLE DA) of rotation for focusing required for attaining an optimal in-focus state with respect to the respective photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m). Note that the amounts of rotation for focusing, which have values for eliminating any displacement of the imaging point at the wide-angle end and the telephoto end, are selected. The lower table summarizes the amounts (DX) of movement, in the direction of the optical axis, of the respective lens units corresponding to the amount (ANGLE DA) of rotation for focusing in association with the photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m) in the respective zooming states with the focal lengths (F=36.0, 50.0, 70.0, 85.0, 105.0, and 131.0 mm). In the lower table, (F) is the focal length (mm) of the entire system, (R) is the photographing distance (m), and (DX) is the amount (mm) of movement, in the direction of the optical axis, of each of the first, second, third, and fourth lens units in turn from the right side. Note that the amount of movement in the direction of the optical axis toward the object side is represented by a positive value.

As can be seen from Table 18, so-called manual focusing can be attained since the displacement amounts of the imaging point at the respective focal lengths and photographing distances are very small, and fall within the depth of focus independently of the zooming state and photographing distance.

The second embodiment is directed to a zoom lens which has a four-unit arrangement, i.e., positive, negative, positive, and positive lens units, and attains focusing by a negative second lens unit. In this zoom lens, the rotation amount ratio (a.sub.F /a.sub.Z) of the rotation amount for focusing from the infinity in-focus position to the closest in-focus position (R=0.5 m) to the amount of rotation for zooming from the wide-angle end (F=28.8) to the telephoto end (F=103.0) is set to be -0.60.

Table 19 below summarizes various paraxial data of an optical system and data for defining the shape of a focus cam according to the second embodiment.

The upper table in Table 19 summarizes the focal lengths and principal point interval data of the respective lens units of the optical system corresponding to the second embodiment in association with six zooming states (focal length F=28.8 (1-POS), 35.0 (2-POS), 50.0 (3-POS), 70.0 (4-POS), 85.0 (5-POS) and 103.0 mm (6-POS)).

The middle table in Table 19 summarizes spline sample data when the shape of the focus cam in the second lens unit of the second embodiment, which is used for focusing, is expressed by a spline function associated with the angle a of rotation of a rotatable lens barrel and the amount x of movement in the direction of the optical axis. In this middle table, (1), (2), (3), and (4) correspond to the first, second, third, and fourth lens units, respectively.

Furthermore, the lower table in Table 19 summarizes the infinity focusing positions (infinity corresponding positions) at the respective focal lengths (F=28.8, 35.0, 50.0, 70.0, 85.0, and 103.0 mm), and the amounts of rotation (amounts of rotation for focusing) upon focusing to respective photographing distances (R=5.0, 3.0, 2.0, 1.0, 0.7, and 0.5 m) using the focus cam of the second embodiment. In this table, since the amount of rotation for zooming from the wide-angle end (F=28.8) to the telephoto end (F=103.0) is set to be 10.0, and the amount of rotation for focusing from the infinity in-focus position to the closest in-focus position (R=0.5 m) is set to be -0.60, the rotation amount ratio (a.sub.F /a.sub.Z) of the amount of rotation for focusing to the amount of rotation for zooming in the second embodiment is

Table 20 below summarizes the numerical value data of the cams of the focusing lens unit in the second embodiment, which data are calculated by interpolation based on a spline function on the basis of the sample data of the focus cam summarized in the middle table in Table 19. Note that the meanings of the reference symbols in Table 20 are the same as those in the first embodiment.

The left table in Table 20 summarizes the numerical value data of the focus cam of the second embodiment, and the right table in Table 20 summarizes the numerical value data of the zoom compensation cam of this embodiment. A value obtained by synthesizing the amounts (2) of movement in the direction of the optical axis in the numerical value data of the focus cam and the zoom compensation cam in the range from the amount of rotation (ANGLE=0.0) to the amount of rotation (ANGLE=10.0) coincides with the movement locus of the second lens unit calculated using the paraxial data in the upper table in Table 19.

Tables 21, 22, and 23 below summarize the amount DX (mm) of movement for focusing, in the direction of the optical axis, of the focusing lens unit, the imaging magnifications .beta..sub.k of the respective lens units, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis, the slope (dx/da) of the focus cam, and the conversion coefficient .gamma..sub.a associated with the direction of rotation at the wide-angle end (F=28.8), the middle position (F=50.0), and the telephoto end (F=103.0) according to the second embodiment, respectively. The arrangements of the respective tables and the meanings of the reference symbols are the same as those in the first embodiment.

As can be seen from Tables 21, 22, and 23, at each focal length, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis increases but the value of the slope (dx/da) of the focus cam decreases as the photographing distance becomes closer to the closest distance. Therefore, as can be seen from these tables, the value of the conversion coefficient .gamma..sub.a associated with the direction of rotation, which is defined as the product of the conversion coefficient .gamma..sub.x and the slope (dx/da) of the focus cam, decreases as the photographing distance becomes closer to the closest distance by the influence of the slope (dx/da) of the focus cam. From Tables 21, 22, and 23, the rate of change, from the infinity in-focus position to the closest in-focus position, of the conversion coefficient .gamma..sub.a associated with the direction of rotation is .times.0.57 at the wide-angle end (F=28.8), .times.0.51 at the middle position (F=50.0), and x0.29 at the telephoto end (F=103.0). When the number N of divisions of the focus range upon a change in conversion coefficient .gamma..sub.a in the second embodiment is calculated using formula (a), and is compared with that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, the numbers N.sub.W, N.sub.M, and N.sub.T of divisions at the wide-angle end, middle position, and telephoto end respectively have the following values:

Embodiment of Japanese Patent Application Laid-Open No. 5-142475

Second Embodiment

Therefore, as can be seen from the above comparison, although the ratio (.DELTA.x.sub.TR /.DELTA.x.sub.WR) between the amounts .DELTA.x.sub.TR and .DELTA.x.sub.WR of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end and the telephoto end in the first embodiment is larger than that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 (the embodiment of Japanese Patent Application Laid-Open No. 5-142475: 3.94; the first embodiment: 4.69), the values of the numbers N of divisions become small.

As described above, in the second embodiment as well, since the rate of change of the conversion coefficient .gamma..sub.a associated with the direction of rotation is smaller than that in the conventional system, the values of the numbers N of divisions become small. For this reason, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. can be reduced, and the storage capacity can be suppressed.

Tables 24, 25, and 26 summarize the calculation results of the conversion coefficient K.sub.a and the correction coefficient .mu. at the wide-angle end (F=28.8), middle position (F=50.0), and telephoto end (F=103.0) according to the second embodiment. The arrangements of the tables and reference symbols are the same as those in the first embodiment. The position of the focusing lens in the first pair in the upper two tables in each of Tables 24, 25, and 26, i.e., in the third and fourth columns is (R, ANGLE)=(0.0, 0.0), and it indicates that this position corresponds to the infinity corresponding position. Similarly, the position of the focusing lens in the fourth pair in the lower two tables in each of Tables 24, 25, and 26, i.e., in the ninth and tenth columns is (R, ANGLE)=(0.5, -6.0), and it indicates that this position corresponds to the closest in-focus (R=0.5 m) corresponding position.

The calculation results of the rate of change of K.sub.a with respect to .gamma..sub.a at the infinity in-focus arrangement and the closest in-focus arrangement at the wide-angle end, middle position, and telephoto end in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and in the second embodiment of the present invention are as follows.

As described above, in the second embodiment as well, since the rate of change of K.sub.a with respect to .gamma..sub.a is small as compared to the conventional system, the contribution of the correction term (.DELTA.Bf/.mu.) in K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) can be reduced. For this reason, an error of the conversion coefficient K.sub.a calculated based on .gamma..sub.a and .mu. or an error from the actual lens driving amount .DELTA.a obtained when only one pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set can be reduced.

Next, in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and the second embodiment of the present invention, when the lens driving amounts upon focusing from the infinity in-focus lens arrangement to the closest distance object and upon focusing from the closest in-focus lens arrangement to the infinity object at the wide-angle end, middle position, and telephoto end are calculated from .DELTA.a=.DELTA.Bf/›.gamma..sub.a (1-.DELTA.Bf/.mu.!, and errors from the actual lens driving amounts are then calculated, the following values are obtained. Note that the value of the correction coefficient p upon focusing from the infinity in-focus lens arrangement to the closest distance object adopts a value at the object distance (POS-5), and the value of the correction coefficient .mu. upon focusing from the closest in-focus lens arrangement to the infinity object adopts a value at the object distance (POS-4).

As described above, in the second embodiment as well, even when only a pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a given lens arrangement range, an error between the conversion coefficient K.sub.a calculated from .gamma..sub.a and .mu. and the lens driving amount .DELTA.a for focusing becomes small as compared to the conventional system, and focusing can be realized with higher accuracy.

Table 27 summarizes the amount (ANGLE DA) of rotation for focusing upon manual focusing using the focus cam (the middle table in Table 19) of the second embodiment, the amount DX (mm) of movement, in the direction of the optical axis, of the focusing lens unit corresponding to the amount of rotation for focusing, and the displacement amount Bf (mm) of the imaging point when the amount (DX) of movement in the direction of the optical axis is given.

Note that the arrangement of the table and reference symbols are the same as those in the first embodiment. The upper table in Table 27 summarizes the displacement amount (Bf) of the imaging point corresponding to the photographing distances (R=5.0, 3.0, 2.0, 1.0, 0.7, and 0.5 m) in the respective zooming states of the focal lengths (F=28.8, 35.0, 50.0, 70.0, 85.0, and 103.0 mm), and the middle table summarizes the values of the amount (ANGLE DA) of rotation for focusing required for attaining an optimal in-focus state with respect to the respective photographing distances. The lower table summarizes the amounts (DX) of movement, in the direction of the optical axis, of the respective lens units corresponding to the amount (ANGLE DA) of rotation for focusing in association with the focal lengths and photographing distances.

As can be seen from Table 27, in the zoom lens of the second embodiment, so-called manual focusing can be attained since the displacement amounts of the imaging point at the respective focal lengths and photographing distances are very small, and fall within the depth of focus independently of the zooming state and photographing distance.

The third embodiment is directed to a zoom lens which has a four-unit arrangement, i.e., positive, negative, positive, and positive lens units, and attains focusing by a negative second lens unit. In this zoom lens, the rotation amount ratio (a.sub.F /a.sub.Z) of the rotation amount for focusing from the infinity in-focus position to the closest in-focus position (R=0.5 m) to the amount of rotation for zooming from the wide-angle end (F=24.7) to the telephoto end (F=116.5) is set to be -0.65.

Table 28 below summarizes various paraxial data of an optical system and data for defining the shape of a focus cam according to the third embodiment.

The upper table in Table 28 summarizes the focal lengths and principal point interval data of the respective lens units of the optical system corresponding to the third embodiment in association with six zooming states (focal length F=24.7 (1-POS), 35.0 (2-POS), 50.0 (3-POS), 70.0 (4-POS), 85.0 (5-POS) and 116.5 mm (6-POS)).

The middle table in Table 28 summarizes spline sample data when the shape of the focus cam in the second lens unit of the third embodiment, which is used for focusing, is expressed by a spline function associated with the angle a of rotation of a rotatable lens barrel and the amount x of movement in the direction of the optical axis. In this middle table, (1), (2), (3), and (4) correspond to the first, second, third, and fourth lens units, respectively.

Furthermore, the lower table in Table 28 summarizes the infinity focusing positions (infinity corresponding positions) at the respective focal lengths (F=24.7, 35.0, 50.0, 70.0, 85.0, and 116.5 mm), and the amounts of rotation (amounts of rotation for focusing) upon focusing to respective photographing distances (R=5.0, 3.0, 2.0, 1.0, 0.7, and 0.5 m) using the focus cam of the third embodiment. In this table, since the amount of rotation for zooming from the wide-angle end (F=24.7) to the telephoto end (F=116.5) is set to be 10.0, and the amount of rotation for focusing from the infinity in-focus position to the closest in-focus position (R=0.5 m) is set to be -6.5, the rotation amount ratio (a.sub.F /a.sub.Z) of the amount of rotation for focusing to the amount of rotation for zooming in the third embodiment is -0.65.

Table 29 below summarizes the numerical value data of the cams of the focusing lens unit in the third embodiment, which data are calculated by interpolation based on a spline function on the basis of the sample data of the focus cam summarized in the middle table in Table 28. Note that the meanings of the reference symbols in Table 29 are the same as those in the first embodiment.

The left table in Table 29 summarizes the numerical value data of the focus cam of the third embodiment, and the right table in Table 29 summarizes the numerical value data of the zoom compensation cam of this embodiment. A value obtained by synthesizing the amounts (2) of movement in the direction of the optical axis in the numerical value data of the focus cam and the zoom compensation cam in the range from the amount of rotation (ANGLE=0.0) to the amount of rotation (ANGLE=10.0) coincides with the movement locus of the second lens unit calculated using the paraxial data in the upper table in Table 28.

Tables 30, 31, and 32 below summarize the amount DX (mm) of movement for focusing, in the direction of the optical axis, of the focusing lens unit, the imaging magnificeations .beta..sub.x of the respective lens units, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis, the slope (dx/da) of the focus cam, and the conversion coefficient .gamma..sub.a associated with the direction of rotation at the wide-angle end (F=24.7), the middle position (F=50.0), and the telephoto end (F=116.5) according to the third embodiment, respectively. The arrangements of the respective tables and the meanings of the reference symbols are the same as those in the first embodiment.

As can be seen from Tables 30, 31, and 32, at each focal length, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis increases but the value of the slope (dx/da) of the focus cam decreases as the photographing distance becomes closer to the closest distance. Therefore, as can be seen from these tables, the value of the conversion coefficient .gamma..sub.a associated with the direction of rotation, which is defined as the product of the conversion coefficient .gamma..sub.x and the slope (dx/da) of the focus cam, decreases as the photographing distance becomes closer to the closest distance by the influence of the slope (dx/da) of the focus cam. From Tables 30, 31, and 32, the rate of change, from the infinity in-focus position to the closest in-focus position, of the conversion coefficient .gamma..sub.a associated with the direction of rotation is .times.0.50 at the wide-angle end (F=24.7), .times.0.45 at the middle position (F=50.0), and .times.0.29 at the telephoto end (F=116.5). When the number N of divisions of the focus range upon a change in conversion coefficient .gamma..sub.a in the third embodiment is calculated using formula (a), and is compared with that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, the numbers N.sub.W, N.sub.M, and N.sub.T of divisions at the wide-angle end, middle position, and telephoto end respectively have the following values:

Embodiment of Japanese Patent Application Laid-Open No. 5-142475

Third Embodiment

As described above, in the third embodiment as well, since the rate of change of the conversion coefficient .gamma..sub.a associated with the direction of rotation is smaller than that in the conventional system so that the values of the numbers N of divisions become small. For this reason, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. can be reduced, and the storage capacity can be suppressed.

Tables 33, 34, and 35 summarize the calculation results of the conversion coefficient K.sub.a and the correction coefficient .mu. at the wide-angle end (F=24.7), middle position (F=50.0), and telephoto end (F=116.5) according to the third embodiment. The arrangements of the tables and reference symbols are the same as those in the first embodiment. The position of the focusing lens in the first pair in the upper two tables in each of Tables 33, 34, and 35, i.e., in the third and fourth columns is (R, ANGLE)=(0.0, 0.0), and it indicates that this position corresponds to the infinity corresponding position. Similarly, the position of the focusing lens in the fourth pair in the lower two tables in each of Tables 33, 34, and 35, i.e., in the ninth and 10th columns is (R, ANGLE)=(0.5, -6.5), and it indicates that this position corresponds to the closest in-focus (R=0.5 m) corresponding position.

The calculation results of the rate of change of K.sub.a with respect to .gamma..sub.a at the infinity in-focus arrangement and the closest in-focus arrangement at the wide-angle end, middle position, and telephoto end in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and in the third embodiment of the present invention are as follows.

As described above, in the third embodiment as well, since the rate of change of K.sub.a with respect to .gamma..sub.a is small as compared to the conventional system, the contribution of the correction term (.DELTA.Bf/.mu.) in K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) can be reduced. For this reason, an error of the conversion coefficient Kacalculated based on .gamma..sub.a and .mu. or an error from the actual lens driving amount .DELTA.a obtained when only one pair of a conversion coefficient .DELTA.a value and a correction coefficient .mu. value are set can be reduced.

Next, in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and the third embodiment of the present invention, when the lens driving amounts upon focusing from the infinity in-focus lens arrangement to the closest distance object and upon focusing from the closest in-focus lens arrangement to the infinity object at the wide-angle end, middle position, and telephoto end are calculated from .DELTA.a=.DELTA.Bf/›.gamma..sub.a (1-.DELTA.Bf/.mu.)!, and errors from the actual lens driving amounts are then calculated, the following values are obtained. Note that the value of the correction coefficient .mu. upon focusing from the infinity in-focus lens arrangement to the closest distance object adopts a value at the object distance (POS-5), and the value of the correction coefficient .mu. upon focusing from the closest in-focus lens arrangement to the infinity object adopts a value at the object distance (POS-4).

As described above, in the third embodiment as well, even when only a pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a given lens arrangement range, an error between the conversion coefficient K.sub.a calculated from .gamma..sub.a and .mu. and the lens driving amount Aa for focusing becomes small as compared to the conventional system, and focusing can be realized with higher accuracy.

Table 36 summarizes the amount (ANGLE DA) of rotation for focusing upon manual focusing using the focus cam (the middle table in Table 28) of the third embodiment, the amount DX (mm) of movement, in the direction of the optical axis:, of the focusing lens unit corresponding to the amount of rotation for focusing, and the displacement amount Bf (mm) of the imaging point when the amount (DX) of movement in the direction of the optical axis is given.

Note that the arrangement of the table and reference symbols are the same as those in the first embodiment. The upper table in Table 36 summarizes the displacement amount (Bf) of the imaging point corresponding to the photographing distances (R=5.0, 3.0, 2.0, 1.0, 0.7, and 0.5 m) in the respective zooming states of the focal lengths (F=24.7, 35.0, 50.0, 70.0, 85.0, and 116.5 mm), and the middle table summarizes the values of the amount (ANGLE DA) of rotation for focusing required for attaining an optimal in-focus state with respect to the respective photographing distances. The lower table summarizes the amounts (DX) of movement, in the direction of the optical axis, of the respective lens units corresponding to the amount (ANGLE DA) of rotation for focusing in association with the focal lengths and photographing distances.

As can be seen from Table 36, in the zoom lens of the third embodiment, so-called manual focusing can be attained since the displacement amounts of the imaging point at the respective focal lengths and photographing distances are very small, and fall within the depth of focus independently of the zooming state and photographing distance.

The fourth embodiment is directed to a zoom lens which has a five-unit arrangement, i.e., positive, negative, positive, negative and positive lens units, and attains focusing by a negative second lens unit. In this zoom lens, the rotation amount ratio (a.sub.F /a.sub.Z) of the rotation amount for focusing from the infinity in-focus position to the closest in-focus position (R=0.8 m) to the amount of rotation for zooming from the wide-angle end (F=28.8) to the telephoto end (F=133.0) is set to be -0.55.

Table 37 below summarizes various paraxial data of an optical system and data for defining the shape of a focus cam according to the fourth embodiment.

The upper table in Table 37 summarizes the focal lengths and principal point interval data of the respective lens units of the optical system corresponding to the fourth embodiment in association with six zooming states (focal length F=28.8 (1-POS), 35.0 (2-POS), 50.0 (3-POS), 70.0 (4-POS), 105.0 (5-POS), and 133.0 mm (6-POS)).

The middle table in Table 37 summarizes spline sample data when the shape of the focus cam in the second lens unit of the fourth embodiment, which is used for focusing, is expressed by the above-mentioned spline function associated with the angle a of rotation of a rotatable lens barrel and the amount x of movement in the direction of the optical axis. In this middle table, (1), (2), (3), (4), and (5) correspond to the first, second, third, fourth, and fifth lens units, respectively.

Furthermore, the lower table in Table 37 summarizes the infinity focusing positions (infinity corresponding positions) at the respective focal lengths (focal length F=28.8, 35.0, 50.0, 70.0, 105.0, and 133.0 mm), and the amounts of rotation (amounts of rotation for focusing) upon focusing to respective photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.8 m) using the focus cam of the fourth embodiment. In this table, since the amount of rotation for zooming from the wide-angle end (F=28.8) to the telephoto end (F=133.0) is set to be 10.0, and the amount of rotation for focusing from the infinity in-focus position to the closest in-focus position (R=0.8 m) is set to be -5.5, the rotation amount ratio (a.sub.F /a.sub.Z) of the amount of rotation for focusing to the amount of rotation for zooming in the fourth embodiment is -0.55.

Table 38 below summarizes the numerical value data of the cams of the focusing lens unit in the fourth embodiment, which data are calculated by interpolation based on a spline function on the basis of the sample data of the focus cam summarized in the middle table in Table 37. Note that the meanings of the reference symbols in Table 38 are the same as those in the first embodiment.

The left table in Table 38 summarizes the numerical value data of the focus cam of the fourth embodiment, and the right table in Table 38 summarizes the numerical value data of the zoom compensation cam of this embodiment. A value obtained by synthesizing the amounts (2) of movement in the direction of the optical axis in the numerical value data of the focus cam and the zoom compensation cam in the range from the amount of rotation (ANGLE=0.0) to the amount of rotation (ANGLE=10.0) coincides with the movement locus of the second lens unit calculated using the paraxial data in the upper table in Table 37.

Tables 39, 40, and 41 below summarize the amount DX (mm) of movement for focusing, in the direction of the optical axis, of the focusing lens unit, the imaging magnifications .beta..sub.k of the respective lens units, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis, the slope (dx/da) of the focus cam, and the conversion coefficient .gamma..sub.a associated with the direction of rotation at the wide-angle end (F=28.8), the middle position (F=70.0), and the telephoto end (F=133.0) according to the fourth embodiment, respectively. The arrangements of the respective tables and the meanings of the reference symbols are the same as those in the first embodiment.

As can be seen from Tables 39, 40, and 41, at each focal length, the conversion coefficient .gamma..sub.x associated with the direction of the optical axis increases but the value of the slope (dx/da) of the focus cam decreases as the photographing distance becomes closer to the closest distance. Therefore, as can be seen from these tables, the value of the conversion coefficient .gamma..sub.a associated with the direction of rotation, which is defined as the product of the conversion coefficient .gamma..sub.x and the slope (dx/da) of the focus cam, decreases as the photographing distance becomes closer to the closest distance by the influence of the slope (dx/da) of the focus cam. From Tables 39, 40, and 41, the rate of change, from the infinity in-focus position to the closest in-focus position, of the conversion coefficient .gamma..sub.a associated with the direction of rotation is .times.0.57 at the wide-angle end (F=28.8), .times.0.45 at the middle position (F=70.0), and .times.0.29 at the telephoto end (F=133.0). When the number N of divisions of the focus range upon a change in conversion coefficient .gamma..sub.a in the fourth embodiment is calculated using formula (a), and is compared with that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475, the numbers N.sub.W, N.sub.M, and N.sub.T of divisions at the wide-angle end, middle position, and telephoto end respectively have the following values:

Embodiment of Japanese Patent Application Laid-Open No. 5-142475

Fourth Embodiment

Therefore, as can be seen from the above comparison, although the ratio (.DELTA.x.sub.TR /.DELTA.x.sub.WR) between the amounts .DELTA.X.sub.TR and .DELTA.X.sub.WR of movement, in the direction of the optical axis, of the focusing lens unit required for focusing from the infinity position to the closest distance position at the wide-angle end and the telephoto end in the first embodiment is larger than that in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 (the embodiment of Japanese Patent Application Laid-Open No. 5-142475: 3.94; the fourth embodiment: 5.49), the values of the numbers N of divisions become small conversely.

As described above, in the fourth embodiment as well, since the rate of change of the conversion coefficient .gamma..sub.a associated with the direction of rotation is smaller than that in the conventional system so that the values of the numbers N of divisions become small. For this reason, the number of data of the conversion coefficient .gamma..sub.a and the correction coefficient .mu. can be reduced, and the storage capacity can be suppressed.

Tables 42, 43, and 44 summarize the calculation results of the conversion coefficient K.sub.a and the correction coefficient .mu. at the wide-angle end (F=28.8), middle position (F=70.0), and telephoto end (F=133.0) according to the fourth embodiment. The arrangements of the tables and reference symbols are the same as those in the first embodiment. The position of the focusing lens in the first pair in the upper two tables in each of Tables 42, 43, and 44, i.e., in the third and fourth columns is (R, ANGLE)=(0.0, 0.0), and it indicates that this position corresponds to the infinity corresponding position. Similarly, the position of the focusing lens in the fourth pair in the lower two tables in each of Tables 42, 43, and 44, i.e., in the ninth and tenth columns is (R, ANGLE)=(0.8, -5.5), and it indicates that this position corresponds to the closest in-focus (R=0.8 m) corresponding position.

The calculation results of the rate of change of K.sub.a with respect to .gamma..sub.a at the infinity in-focus arrangement and the closest in-focus arrangement at the wide-angle end, middle position, and telephoto end in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and in the fourth embodiment of the present invention are as follows.

As described above, in the fourth embodiment as well, since the rate of change of K.sub.a with respect to .gamma..sub.a is small as compared to the conventional system, the contribution of the correction term (.DELTA.Bf/.mu.) in K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) can be reduced. For this reason, an error of the conversion coefficient K.sub.a calculated based on .gamma..sub.a and .mu. or an error from the actual lens driving amount .DELTA.a obtained when only one pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set can be reduced.

Next, in the embodiment of Japanese Patent Application Laid-Open No. 5-142475 and the fourth embodiment of the present invention, when the lens driving amounts upon focusing from the infinity in-focus lens arrangement to the closest distance object and upon focusing from the closest in-focus lens arrangement to the infinity object at the wide-angle end, middle position, and telephoto end are calculated from .DELTA.a=.DELTA.Bf/›.gamma..sub.a (1-.DELTA.Bf/.mu.)!, and errors from the actual lens driving amounts are then calculated, the following values are obtained. Note that the value of the correction coefficient .mu. upon focusing from the infinity in-focus lens arrangement to the closest distance object adopts a value at the object distance (POS-5), and the value of the correction coefficient .mu. upon focusing from the closest in-focus lens arrangement to the infinity object adopts a value at the object distance (POS-4).

As described above, in the fourth embodiment as well, even when only a pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a given lens arrangement range, an error between the conversion coefficient K.sub.a calculated from .gamma..sub.a and .mu. and the lens driving amount .DELTA.a for focusing becomes small as compared to the conventional system, and focusing can be realized with higher accuracy.

Table 45 summarizes the amount (ANGLE DA) of rotation for focusing upon manual focusing using the focus cam (the middle table in Table 37) of the fourth embodiment, the amount DX (mm) of movement, in the direction of the optical axis, of the focusing lens unit corresponding to the amount of rotation for focusing, and the displacement amount Bf (mm) of the imaging point when the amount (DX) of movement in the direction of the optical axis is given.

Note that the arrangement of the table and reference symbols are the same as those in the first embodiment. The upper table in Table 45 summarizes the displacement amount (Bf) of the imaging point corresponding to the photographing distances (R=5.0, 3.0, 2.0, 1.5, 1.0, and 0.80 m) in the respective zooming states of the focal lengths (F=28.8, 35.0, 50.0, 70.0, 105.0, and 133.0 mm), and the middle table summarizes the values of the amount (ANGLE DA) of rotation for focusing required for attaining an optimal in-focus state with respect to the respective photographing distances. The lower table summarizes the amounts (DX) of movement, in the direction of the optical axis, of the respective lens units corresponding to the amount (ANGLE DA) of rotation for focusing in association with the focal lengths and photographing distances.

As can be seen from Table 45, so-called manual focusing can be attained since the displacement amounts of the imaging point at the respective focal lengths and photographing distances are very small, and fall within the depth of focus independently of the zooming state and photographing distance.

As described above in the embodiments, the present invention can be applied to zoom lens systems based on various lens unit arrangements or focusing lens units.

As described above, according to the present invention, in an inner focusing type zoom lens which is attached to, e.g., an auto-focusing camera which has focus detection means, storage means, calculation means, and the like, the number of data of specific coefficients (e.g., the conversion coefficient .gamma..sub.a and the correction coefficient .mu.) required for auto-focusing can be reduced as compared to the conventional system. Furthermore, an error upon calculation of the lens driving amount of the focusing lens unit using the stored specific coefficients in correspondence with the detected defocus amount can be reduced as compared to the conventional system.

In other words, when the arrangement of the present invention is adopted, since the rate of change of the conversion coefficient .gamma..sub.a is reduced as compared to the conventional system, the number of data of the conversion coefficient .gamma..sub.a, the correction coefficient .mu., and the like which are stored for calculating the lens driving amount for focusing can be reduced, and a cost reduction can be realized in terms of the storage capacity.

Furthermore, since the change in conversion coefficient K.sub.a to the conversion coefficient .gamma..sub.a becomes small, the contribution of the correction term (.DELTA.Bf/.mu.) in K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) can be reduced.

Therefore, an error of the conversion coefficient K.sub.a calculated based on .gamma..sub.a and .mu. or an error from the actual lens driving amount .DELTA.a obtained when only one pair of a conversion coefficient .gamma..sub.a value and a correction coefficient .mu. value are set for a certain lens arrangement range can be reduced.

In the present invention, the conversion coefficient .gamma..sub.a at an in-focus point and the conversion coefficient .mu. which is defined by formula K.sub.a =.gamma..sub.a (1-.DELTA.Bf/.mu.) are set to be specific coefficients. Alternatively, a correction coefficient defined by a formula different from the above-mentioned formula may be set. Furthermore, the conversion coefficient .gamma..sub.a need not always be set in correspondence with the sensitivity (dBf/da) associated with the direction of rotation at an in-focus point. As long as focusing accuracy can be improved, the sensitivity at a point other than the in-focus point and the corresponding correction coefficient may be set to be specific coefficients.

Note that the present invention can be applied to various other zoom lens systems based on lens unit arrangements or focusing lens units other than those in the above-mentioned embodiments, as a matter of course.