Zoom Lens System

1. Field of the Invention

The present invention relates to a zoom lens system, more particularly to a zoom lens system that is suitable to close-up shooting.

2. Description of the Prior Art

In a zoom lens system, the focusing in close-up shooting is most commonly achieved by moving out one lens unit. This focusing method conveniently allows, among other things, the lens barrel construction to be simplified, on one hand, but it inconveniently causes the aberration to deteriorate as the closest shooting distance is made shorter, and also demands rather a large lens unit to be moved for focusing, on the other hand. For these reasons, other methods such as the internal focusing method and the rear focusing method have been proposed as substitutes for the above described method.

In particular, the internal focusing method conveniently allows, among other things, the closest shooting distance to be made shorter, the focusing lens unit to be made smaller and lighter, the focusing movement amount to be made smaller, and the aberration to deteriorate less. For these reasons, this focusing method is adopted in more and more commercial products nowadays. For example, various conventional zoom lens systems are known which include a positive lens unit and a negative lens unit in this order from the object-side end, and in which the second lens unit is used as a focusing lens unit. There, the internal focusing using the second lens unit contributes to the reduction of aberration in close-up shooting.

However, even though the deterioration of the aberration is reduced in this type of zoom lens system, the aberration does deteriorate anyway at close shooting distances, and the deterioration becomes severer as the shooting distance becomes shorter. Especially, at a shooting magnification .beta. exceeding about -1/4, the aberration deterioration (the inclination of the image surface, in particular) grows so great that it is no more possible to secure practical optical performance.

Moreover, a zoom lens system is also known which consists of four lens units, that is, positive, negative, positive, and positive lens units, and in which all the lens units are movable. This construction makes it easy to widen the zooming range and to correct aberration.

However, when the second lens unit is used as a focusing lens unit in a four-lens-unit zoom lens system consisting of positive, negative, positive, and positive lens units, the movement amount of the focusing lens unit becomes greater as the closest-shooting-distance is made shorter. An attempt to secure the space for the movement results in a longer total length of the zoom lens system, and an attempt to strengthen the refractive power of the second lens to make the focusing movement amount smaller leads to more complicated aberration compensation.

An object of the present invention is to provide a zoom lens system that suffers less aberration deterioration even when the closest shooting distance is made shorter.

Another object of the present invention is to provide a zoom lens system that offers a shorter closest shooting distance, compactness, and a high degree of optical performance at the same time.

To achieve the above objects, according to the present invention, a zoom lens system comprises, from the object-side end, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, and, closer to the image-surface-side end than the second lens, an nth lens unit having a positive refractive power and an (n+1)th lens unit having a positive refractive power. During zooming, at least the first lens unit moves. During focusing, the second lens unit moves at the same time as the distance between the nth and (n+1)th lens units varies.

In a zoom lens system as described above, which comprises, from the object-side end, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, and, closer to the image-surface-side end than the second lens, an nth lens unit having a positive refractive power and an (n+1)th lens unit having a positive refractive power, and in which at least the first lens unit moves during zooming and the second lens unit moves during focusing, the spherical aberration varies only slightly, whereas the inclination of the image surface becomes greater as the shooting magnification becomes greater. In the present invention, this inclination of the image surface is corrected without much affecting other types of aberration by varying the distance between the nth and (n+1)th lens units as described below.

The first lens unit makes axial light rays converge, and the second lens unit then makes them diverge. Ultimately, the two adjacent positive lens units (the nth and (n+1)th lens units) make the light rays converge. Meanwhile, since the nth and (n+1)th lens units have the same effect on axial light rays, the angle that a light ray forms with respect to the optical axis between the nth and (n+1)th lens units is within the range between the angle that the light ray forms with respect to the optical axis when entering the nth lens unit and the angle that the light ray forms with respect to the optical axis when exiting from the (n+1)th lens unit. This means that the light rays are nearly parallel to the optical axis between the nth and (n+1)th lens units. Consequently, even when the distance between the nth and (n+1)th lens units varies, axial light rays do not suffer so much aberration. On the other hand, off-axial light rays form greater angles with respect to the optical axis between the nth and (n+1)th lens units. Consequently, when the distance between the nth and (n+1)th lens units varies, off-axial light rays suffer a greater change of the image surface. Accordingly, by varying the distance between the nth and (n+1)th lens units, the inclination of the image surface resulting from the focusing using the second lens unit can be corrected.

According to one feature of the present invention, it is desirable that a zoom lens system consist of four lens units, that is, from the object-side end, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. This is because a construction in which all the lens units are movable makes it easy to widen the zooming range and to correct aberration. Moreover, in this four-lens-unit construction, it is desirable that the third lens unit in addition to the second lens unit be moved during focusing, or that the fourth lens unit in addition to the second lens unit be moved during focusing, or that the third and fourth lens units in addition to the second lens unit be moved during focusing.

Moreover, in the present invention, it is desirable that the focusing movement amount of the second lens unit and the amount of change in the distance between the nth and (n+1)th lens units satisfy the following conditional expression (1). When the conditional expression (1) is satisfied, inclination of the image surface in shooting at the closest shooting distance can be corrected more effectively.

where

x.sub.2 : focusing movement amount of the second lens unit;

.DELTA.x.sub.n,n+1 : amount of change in the varying distance between the nth and (n+1)th lens units during focusing.

Furthermore, in the present invention, it is desirable that the above amount of change .DELTA.x.sub.n,n+1 vary only with the shooting distance but not with zooming. This is because such a construction helps to simplify the lens barrel construction. It is of course possible to allow the amount of change to vary with zooming.

According to another feature of the present invention, a zoom lens system comprises four lens units, that is, from the object-side end, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. During zooming from the wide-angle end to the telephoto end, all the lens units move in such a way that the distance between the first and second lens units increases and the distance between the second and third lens units decreases. During focusing for close-up shooting, the second lens unit moves toward the object side. Furthermore, the following conditional expressions (2) to (4) are satisfied:

where

f.sub.1 : focal length of the first lens unit;

f.sub.2 : focal length of the second lens unit;

f.sub.3 : focal length of the third lens unit;

f.sub.4 : focal length of the fourth lens unit;

.beta..sub.2T : horizontal magnification of the second lens unit at the longest-focal-length end;

.beta..sub.2W : horizontal magnification of the second lens unit at the shortest-focal-length end;

Z: zoom ratio.

In the four-lens-unit construction as described above which consists of, from the object-side end, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power, and in which all the lens units are movable, it is easier to widen the zooming range and to correct aberration.

The conditional expression (2) defines the ratio of the refractive power of the first lens unit to that of the second lens unit. When the refractive power of the second lens unit (focusing lens unit) is weaker than that of the first lens unit to such an extent that the lower limit of the conditional expression (2) is exceeded, the movement amount of the second lens unit during focusing for close-up shooting increases, requiring more space to be secured. This makes the total length of the zoom lens system longer and impairs compactness. Moreover, since the distance between the first and second lens units in the infinite-shooting-distance state (object distance =.infin.) becomes longer, it is difficult to secure sufficient illuminance on the image surface. To reduce the closest shooting distance without impairing compactness, the refractive power of the second lens unit needs to be strengthened. However, when the refractive power of the second lens unit is stronger than that of the first lens unit to such an extent that the upper limit of the conditional expression (2) is exceeded, it is difficult to correct aberrations, especially off-axial coma aberration at the wide-angle end.

The conditional expression (3) defines the ratio of the refractive power of the third lens unit to that of the fourth lens unit. When the refractive power of the third lens unit is stronger than that of the fourth lens unit to such an extent that the lower limit of the conditional expression (3) is exceeded, it is difficult to correct spherical aberration. Reversely, when the refractive power of the fourth lens unit is stronger than that of the third lens unit to such an extent that the upper limit of the conditional expression (3) is exceeded, it is difficult to correct off-axial aberrations, especially sagittal coma aberration, which increases as the whole system is made more compact.

The conditional expression (4) defines the zooming ratio of the second lens unit to that of the whole zoom lens system. To reduce the second lens unit's share of the zooming ratio, either the movement amounts of the third and fourth lens units during zooming need to be made greater, or the refractive powers of the third and fourth lens units need to be made stronger. Reversely, to increase the second lens unit's share of the zooming ratio, either the movement amount of the second lens unit during zooming needs to be made greater, or the refractive power of the second lens unit needs to be made stronger. Therefore, when the second unit's share of the zooming ratio is so small that the lower limit of the conditional expression (4) is exceeded, either the increase in the movement amounts of the third and fourth lens units during zooming impairs compactness, or the excessive refractive powers of the third and fourth lens units make it difficult to correct aberrations, especially spherical aberration and off-axial coma aberration. Reversely, when the second unit's share of the zooming ratio is so large that the upper limit of the conditional expression (4) is exceeded, either the increase in the movement amount of the second lens unit during zooming impairs compactness, or the excessive refractive power of the second lens unit makes it difficult to correct aberrations, especially coma aberration, which affects off-axial optical performance at the wide-angle end.

To achieve a higher degree of compactness and optical performance in a construction according to the present invention, it is preferable that the fourth lens unit include at least one aspherical surface. When the fourth lens unit includes an aspherical surface, it is easy to correct, in particular, sagittal coma aberration, which increases as the whole system is made more compact.

This and other objects and features of this invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanied drawings in which:

FIG. 1 is a lens construction diagram showing the zooming operation in the infinite-shooting-distance state of the first to third and fifth embodiments of the present invention and of a comparison example;

FIGS. to 2A to 2I are diagrams showing aberrations in the infinite-shooting-distance state of the first to third and fifth embodiments and the comparison example;

FIG. 3 is a lens construction diagram showing the focusing operation at the wide-angle end of the first embodiment;

FIGS. 4A to 4I are diagrams showing aberrations in the closest-shooting-distance state of the first embodiment;

FIG. 5 is a lens construction diagram showing the focusing operation at the wide-angle end of the second embodiment;

FIGS. 6A to 6I are diagrams showing aberrations in the closest-shooting-distance state of the second embodiment;

FIG. 7 is a lens construction diagram showing the focusing operation at the wide-angle end of the third embodiment;

FIGS. 8A to 8I are diagrams showing aberrations in the closest-shooting-distance state of the third embodiment;

FIG. 9 is a lens construction diagram showing the closest-shooting-distance shooting-distance state at the wide-angle end of the comparison example;

FIG. 10A to 10I are diagrams showing aberrations in the closest-shooting-distance state of the comparison example;

FIG. 11 is a lens construction diagram showing the zooming operation in the infinite-shooting-distance state of the fourth embodiment of the present invention;

FIGS. 12A to 12I ediagrams showing aberrations in the infinite-shooting-distance state of the fourth embodiment;

FIG. 13 is a lens construction diagram showing the closest-shooting-distance state a the wide-angle end of the fourth embodiment;

FIGS. 14A to 14I are diagrams showing aberrations in the closest-shooting-distance state of the fourth embodiment;

FIG. 15 is a lens construction diagram showing the closest-shooting-distance state at the wide-angle end of the fifth embodiment;

FIGS. 16A to 16I diagrams showing aberrations in the closest-shooting-distance state of the fifth embodiment;

FIG. 17 is a lens construction diagram showing the zooming operation in the infinite-shooting-distance state of the sixth embodiment of the present invention;

FIGS. 18A to 18I diagrams showing aberrations in the infinite-shooting distance state of the sixth embodiment;

FIG. 19 is a lens construction diagram showing the closest-shooting-distance state at the wide-angle end of the sixth embodiment;

FIGS. to 20A to 20I are diagrams showing aberrations in the closest-shooting-distance state of the sixth embodiment;

FIG. 21 is a lens construction diagram showing the zooming operation in the infinite-shooting-distance state of the seventh embodiment of the present invention;

FIGS. 22A to 22I are diagrams showing aberrations in the infinite-shooting-distance state of the seventh embodiment;

FIG. 23 is a lens instruction diagram showing the closest-shooting-distance state at the wide-angle end of the seventh embodiment;

FIGS. 24A to 24I are diagrams showing aberrations in the closest-shooting-distance of the seventh embodiment;

FIG. 25 is a lens instruction diagram showing the infinite-shooting-distance state at the wide-angle end of the eighth to eleventh embodiments of the present invention;

FIGS. 26A to 26I are diagrams showing aberrations in the infinite-shooting-distance state of the eighth to eleventh embodiments;

FIG. 27 is a lens construction diagram showing the closest-shooting-distant state at the wide-angle end of the eighth embodiment;

FIGS. 28A to 28I are diagrams showing aberrations in the closest-shooting state of the eighth embodiment;

FIG. 29 is a lens construction diagram showing the closest-shooting-distance state at the wide-angle end of the ninth embodiment;

FIGS. 30A to 30I are diagrams showing aberrations in the closest-shooting-distance state of the ninth embodiment;

FIG. 31 is a lens construction diagram showing the closest-shooting-distance state at the wide-angle end of the tenth embodiment;

FIGS. 32A to 32I are diagrams showing aberrations in the closest-shooting-distance state of the tenth embodiment;

FIG. 33 is a lens construction diagram showing the closest-shooting-distance state at the wide-angle end of the eleventh embodiment;

FIGS. 34A to 34I are diagrams showing aberrations in the closest-shooting-distance state of the eleventh embodiment.

FIGS. 35A to 35C are diagrams showing the zooming operation of the eighth to eleventh embodiments;

FIGS. 36A to 36C are diagrams showing the focusing operation of the eighth embodiment;

FIGS. 37A to 37C are diagrams showing the focusing operation of the ninth embodiment;

FIGS. 38A to 38C diagrams showing the focusing operation of the tenth embodiment; and

FIGS. 39A to 39C are diagrams showing the focusing operation of the eleventh embodiment.

Hereinafter, zoom lens systems according to the present invention will be described with reference to the drawings. FIGS. 3, 5, and 7 are lens construction diagrams corresponding to the zoom lens systems of the embodiments 1, 2, and 3, respectively. Each figure shows lens arrangements in the infinite-shooting-distance state ›W(.infin.)!, and the closest-shooting-distance state ›W(D)!, both at the wide-angle end. In each lens construction diagram, the arrows M2, M3, and M4 schematically indicate the focusing or floating movement of the second, third, and fourth lens units Gr2, Gr3, and Gr4, respectively, from the infinite-shooting-distance state ›W(.infin.)! to the closest-shooting-distance state ›W(D)! at the wide-angle end. Further, d5 represents the axial distance between the first and second lens units Gr1 and Gr2, d13 represents the axial distance between the second and third lens units Gr2 and Gr3, and d19 represents the axial distance between the third and fourth lens units Gr3 and Gr4.

The zoom lens systems of the embodiments 1 to 3 each consist of, from the object-side end, a first lens unit Gr1 having a positive refractive power, a second lens unit Gr2 having a negative refractive power, a third lens unit Gr3 having positive refractive power, and a fourth lens unit Gr4 having a positive refractive power. The first lens unit Gr1 is composed of, from the object-side end, a composite lens of a negative meniscus lens with its concave surface facing toward the image side and a biconvex positive lens, and a positive meniscus lens with its convex surface facing toward the object side. The second lens unit Gr2 is composed of, from the object-side end, a negative meniscus lens with its concave surface facing toward the image side, a biconcave negative lens, a biconvex positive lens, and a negative meniscus lens with its concave surface facing toward the object side. The third lens unit Gr3 is composed of, from the object-side end, an aperture diaphragm, a biconvex positive lens, and a composite lens of a biconvex positive lens and a biconcave negative lens. The fourth lens unit Gr4 is composed of, from the object-side end, a biconvex positive lens, and a biconcave negative lens whose object-side surface is an aspherical surface.

The focusing movement of the second lens unit Gr2 achieves internal focusing. Since, during this focusing, the floating movement of the third and fourth lens units Gr3 and Gr4 causes the axial distance d19 between them to vary, the inclination of the image surface resulting from the focusing using the second lens unit Gr2 is corrected. During zooming from the wide-angle end to the telephoto end, all the lens units Gr1 to Gr4 moves forward. As described earlier, this construction in which all the lens units are movable makes it easy to widen the zooming range and to correct aberration.

Hereinafter, the zoom lens systems of the embodiments 1 to 3, together with an example for comparison, will be described more specifically in terms of construction, with reference to their construction data, aberration performance, and other characteristics. In the construction data, ri (i=1, 2, 3, . . . ) represents the curvature radius of the i-th surface from the object-side end, di (i=1, 2, 3, . . . ) represents the i-th axial distance from the object-side end, and Ni (i=1, 2, 3, . . . ) and vi (i=1, 2, 3, . . . ) represent the d-lines refractive coefficient (Nd) and the Abbe number (vd) of the i-th lens from the object-side end. A surface whose curvature radius (ri) is marked with an asterisk (*) is an aspherical surface. Suppose that the shape of such a surface is defined by the following expression (A). ##EQU1## where X: displacement from the reference surface of the optical axis direction;

Y: height in the direction perpendicular to the optical axis;

C: paraxial curvature;

.epsilon.: quadric surface parameter;

Ai (i=1, 2, 3 . . . ): aspherical coefficient.

First, the construction data of the embodiments 1 to 3 and the comparison example will be shown below, together with the axial distances (d5, d13, d19) that vary with zooming in the infinite-shooting-distance state. In addition, the focal lengths f and the f-numbers FNO of the whole system at the wide-angle end ›W(.infin.)!, at the midpoint (medium focal length state) ›M(.infin.)!, and at the telephoto end ›T(.infin.)! in the infinite-shooting-distance state are also shown below.

FIG. 1 shows the lens construction of the embodiments 1 to 3 and the comparison example, which are represented by the above construction data, in the infinite-shooting-distance state at the wide-angle end ›W(.infin.)!, and the movements of the lens units Gr1 to Gr4 from that state ›W(.infin.)! to the infinite-shooting-distance state at the telephoto end ›T(.infin.)!. In FIG. 1, the arrows m1 to m4 indicate the movements of the lens units Gr1 to Gr4, respectively. These movements of the lens units Gr1 to Gr4 (each moves forward) effect zooming (f=22.5 to 78.0 mm) in the embodiments 1 to 3 and in the comparison example, thereby allowing the view of angle 2.omega. to vary in the range between 75.degree. and 25.degree..

Tables 1 to 4 below list the axial distances (d5, d13, d19), the shooting magnifications .beta., and the effective f-numbers FNO at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)! in the closest-shooting-distance state (shooting distance=0.25 m) of the embodiments 1 to 3 and the comparison example.

Tables 5 to 8 below list the movement amount and the values corresponding to the conditional expression (1) above of the second to fourth lens units Gr2 to Gr4 at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)! during focusing (from the infinite-shooting-distance state to the closest-shooting-distance state, shooting distance=0.25 m) of the embodiments 1 to 3 and the comparison example.

FIG. 2 shows aberration curves of the embodiments 1 to 3 and the comparison example in the infinite-shooting-distance state, illustrating aberrations at the wide-angle end ›W(.infin.)!, at the midpoint ›M(.infin.)!, and at the telephoto end ›T(.infin.)!. FIGS. 4, 6, 8, and 10 show aberration curves of the embodiments 1 to 3 and the comparison example, respectively, in the closest-shooting-distance state, illustrating aberrations at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)!. In these figures, solid lines (d) represent d-lines aberrations, broken lines (SC) represent sine conditions, and broken lines (DM) and solid lines (DS) represent astigmatisms on the meridional image surface and on the sagittal image surface, respectively.

In the embodiments 1 to 3, the inclination of the image surface resulting from the focusing movement of the second lens unit Gr2 (indicated by arrow M2 in each figure) is corrected by the variation in distance d19 between the third and fourth lens unit Gr3 and Gr4. The variation in distance d19 between the third and fourth lens unit Gr3 and Gr4 is achieved by the floating movement (arrow M3) of the third lens unit Gr3 toward the object side during focusing in the embodiment 1, by the floating movement (arrow M4) of the fourth lens unit Gr4 toward the image-surface side during focusing in the embodiment 2, and by the floating movement (arrow M3) of the third lens unit Gr3 toward the object side and the floating movement (arrow M4) of the fourth lens unit Gr4 toward the image-surface side during focusing in the embodiment 3.

In the comparison example, focusing is achieved by simply moving the second lens unit Gr2, without any floating. FIG. 9 shows the lens arrangement of this comparison example in the closest-shooting-distance state at the wide-angle end ›W(D)!. From the aberration curves in FIG. 10, it is seen that the image surface inclines downward at each shooting magnification .beta.(=-0.12 to -0.28). The inclination of the image surface is especially striking at the telephoto end ›T(D)! where the shooting magnification exceeds -1/4 and reaches -1/3.6. In addition, the inclination of the image surface also impairs the optical performance even at the wide-angle end ›W(D)!.

By contrast, in the embodiments 1 to 3, the inclination of the image surface is properly corrected at the shooting magnifications similar to those used with the comparison example (see the aberration curves in FIGS. 2, 4, 6, and 8). Consequently, it is possible to maintain the image-surface in a good condition over the whole range from infinite to closest shooting distances. Furthermore, in the embodiments 1 to 3, the distance d19, which is varied for image-surface correction, is kept constant even during zooming as long as the shooting distance is kept constant. This is because such a method allows the cam construction to be simplified. It is of course possible to allow the distance d19 to vary with zooming in order to achieve better image-surface correction.

As described above, according to the present invention, during focusing, while the second lens unit moves, the distance between the nth and (n+1)th lens units varies. This keeps aberration deterioration small even when the closest shooting distance is made shorter. As a result, it is possible to shoot an object at closer distances than ever.

Note that the present invention can also be applied to a zoom lens system consisting of five or more lens units.

Hereinafter, zoom lens systems according to the present invention will be described with reference to the drawings. FIGS. 11, 1, 17, and 21 are lens construction diagrams corresponding to the zoom lens systems of the embodiments 4, 5, 6, and 7, respectively, each illustrating lens arrangements in the infinite-shooting-distance state ›W(.infin.)! at the wide-angle end. In each lens construction diagram, ri (i=1, 2, 3, . . . ) represents the curvature radius of the i-th surface from the object-side end, di (i=1, 2, 3, . . . ) represents the i-th axial distance from the object-side.

The zoom lens systems of the embodiment 4 to 7 consist of four lens units, that is, from the object-side end, a first lens unit Gr1 having a positive refractive power, a second lens unit Gr2 having a negative refractive power, a third lens unit Gr3 having a positive refractive power, and a fourth lens unit Gr4 having a positive refractive power. The lens units Gr1 to Gr4, as indicated by corresponding arrows m1 to m4 in each lens construction diagram, all move forward during zooming from the wide-angle end ›W(.infin.)! to the telephoto end ›T(.infin.)! in such a way that the distance between the first and second lens units Gr1 and Gr2 increases and the distance between the second and third lens units Gr2 and Gr3 decreases. As described earlier, this construction in which all the lens units are movable makes it easy to widen the zooming range and to correct aberration.

In the embodiments 4, 6, and 7, the first lens unit Gr1 is composed of, from the object-side end, a composite lens of a negative meniscus lens with its concave surface facing toward the image side and a biconvex lens, and a positive meniscus lens with its convex surface facing toward the object side. The second lens unit Gr2 is composed of, from the object-side end, a negative meniscus lens with its concave surface facing toward the image side, a biconcave negative lens, a positive meniscus lens with its convex surface facing toward the object side, and a negative meniscus lens with its concave surface facing toward the object side. The third lens unit Gr3 is composed of, from the object-side end, an aperture diaphragm, two biconvex positive lens, and a negative meniscus lens with its concave surface facing toward the object side. The fourth lens unit Gr4 is composed of, from the object-side end, a biconvex positive lens, and a biconcave negative lens whose object-side surface is an aspherical surface.

In the embodiment 5, as shown in FIG. 1, the first lens unit Gr1 is composed of, from the object-side end, a composite lens of a negative meniscus lens with its concave surface facing toward the image side and a biconvex positive lens, and a positive meniscus lens with its convex surface facing toward the object side. The second lens unit Gr2 is composed of, from the object-side end, a negative meniscus lens with its concave surface facing toward the image side, a biconcave negative lens, a biconvex positive lens, and a negative meniscus lens with its concave surface facing toward the object side. The third lens unit Gr3 is composed of, from the object-side end, an aperture diaphragm, a biconvex positive lens, and a composite lens of a biconvex positive lens and a biconcave negative lens. The fourth lens unit Gr4 is composed of, from the object-side end, a biconvex positive lens, and a biconcave negative lens whose object-side surface is an aspherical surface.

FIGS. 13, 15, 19, and 23 are lens construction diagrams corresponding to the zoom lens systems of the embodiments 4, 5, 6, and 7, respectively, each illustrating lens arrangements in the closest-shooting-distance state ›W(D)! at the wide-angle end. As seen from these diagrams, in any of these embodiments, the second lens unit Gr2 moves toward the object side during focusing for close-up shooting. However, since the refractive power of the second lens unit Gr2 is strengthened to satisfy the above conditional expressions (2) and (4), a high degree of optical performance is obtained even when the closest shooting distance is made shorter. As a result, it is possible to shoot an object at closer distances than ever. Moreover, since the refractive power of the fourth lens unit Gr4 is weakened by satisfying the above conditional expressions (3) and (4), the deterioration of the off-axial optical performance (especially sagittal coma aberration and the like), as occurs when the whole system is made more compact, is reduced. As a result, it is possible to make the whole zoom lens system more compact at the same as realizing a high degree of optical performance.

Hereinafter, the zoom lens systems of the embodiments 4 to 7 will be described more specifically in terms of construction, with reference to their construction data, aberration performance, and other characteristics. The construction data of the embodiments 4, 5, 6, and 7 are shown on the Tables 10, 1, 11, and 12. In the construction data, ri (i=1, 2, 3, . . . ) represents the curvature radius of the i-th surface from the object-side end, di (i=1, 2, 3, . . . ) represents the i-th axial distance from the object-side end, and Ni (i=1, 2, 3, . . .) and .nu.i (i=1, 2, 3, . . .) represent the d-lines refractive coefficient (Nd) and the Abbe number (.nu.d) of the i-th lens from the object-side end. In the construction data, the axial distances that vary with zooming represent the distances between the lens units at the wide-angle end ›W(.infin.)!, at the midpoint (medium focal length state) ›M(.infin.)!, and at the telephoto end ›T(.infin.)! in the infinite-shooting-distance state, and these values are shown together with the focal lengths f and the f-numbers FNO of the whole system in respective states. A surface whose curvature radius (ri) is marked with an asterisk (*) is an aspherical surface. Suppose that the shape of such a surface is defined by the above-described expression (A).

In the embodiment 4, as shown in FIG. 11, the lens units Gr1 to Gr4 move forward (m1 to m4) to effect zooming (f=28.8 to 82.0 mm). The zooming allows the angle of view 2.omega. to vary between 62.degree. to 24.degree.. In the embodiment 5, as shown in FIG. 1, the lens units Gr1 to Gr4 move forward (m1 to m4) to effect zooming (f=22.5 to 78.0 mm). The zooming allows the angle of view 2.omega. to vary between 75.degree. to 25.degree.. In the embodiment 6, as shown in FIG. 17, the lens units Gr1 to Gr4 move forward (m1 to m4) to effect zooming (f=22.6 to 78.0 mm). The zooming allows the angle of view 2.omega. to vary between 75.degree. to 25.degree.. In the embodiment 7, as shown in FIG. 21, the lens units Gr1 to Gr4 move forward (m1 to m4) to effect zooming (f=22.6 to 78.0 mm). The zooming allows the angle of view 2.omega. to vary between 75.degree. to 25.degree..

Tables 13 to 16 below list the axial distances d5, d13, d19, and d20 that vary with focusing, the shooting magnifications .beta., and the effective f-numbers FNO at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)! in the closest-shooting-distance state of the embodiments 4 to 7. The lens arrangement of each embodiment in the closest-shooting-distance state at the wide-angle end ›W(D)! is shown in FIGS. 13, 15, 19, and 23.

FIGS. 12A to 12I, 2A to 2I, 18A to 18I, and 22A to 22I show aberration curves of the embodiments 4 to 7, respectively, in the infinite-shooting-distance state, illustrating aberrations at the wide-angle end ›W(.infin.)!, at the midpoint ›M(.infin.)!, and at the telephoto end ›T(.infin.)!. FIGS. 14A to 14I, 16A to 16I, 20A to 20I, and 24A to 24I show aberration curves of the embodiments 4 to 7, respectively, in the closest-shooting-distance state, illustrating aberrations at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)!. In these figures, solid lines (d) represent d-lines aberrations, broken lines (SC) represent sine conditions, and broken lines (DM) and solid lines (DS) represent astigmatisms on the meridional image surface and on the sagittal image surface, respectively.

In any of these embodiments 4 to 7, the second lens unit Gr2 moves as a focusing lens unit. However, since the above-mentioned conditional expressions (2) and (4) are satisfied, a high degree of optical performance is obtained even when the closest shooting distance is made shorter. As a result, it is possible to shoot an object at closer distances than ever. Moreover, since the above-mentioned conditional expressions (3) and (4) are satisfied, the deterioration of the off-axial optical performance (especially sagittal coma aberration and the like), as occurs when the whole system is made more compact, is reduced. As a result, it is possible to make the whole zoom lens system more compact at the same as realizing a high degree of optical performance.

Next, the embodiments 8 to 11 of the present invention will be described below. The zoom lens systems of these embodiments consist of five lens units. Of the five lens units, the first to fourth lens units Gr1 to Gr4 are substantially the same as the lens units in the above-described embodiments 1 to 7. The fifth lens unit Gr5 is composed of a weakly negative meniscus lens with its convex surface facing toward the image-side end. This lens has aspherical surfaces on its both sides. The fifth lens unit Gr5 is stationary, and therefore it does not move either during zooming or during focusing.

Table 18 shows the construction data of the embodiments 8 to 11 together with the axial distance (d5, d13, d19, d23) that vary with zooming in the infinite-shooting-distance state. In addition, the focal length f and the f-number FNO of the whole system at the wide-angle end ›W(.infin.)!, at the midpoint (medium focal length state) ›M(.infin.)!, and at the telephoto end ›T(.infin.)! in the infinite-shooting-distance state are also shown in Table 18.

FIG. 25 shows the lens construction of the embodiments 8 to 11 which are represented by the construction data of the table 18 in the infinite-shooting-distance state at the wide-angle end ›W(.infin.)!.

Tables 19 to 22 below list the axial distances (d5, d13, d19, d23), the shooting magnification .beta., and the effective numbers FNO at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)! in the closest-shooting-distance state (shooting distance=0.25 m) of the embodiments 8 to 11.

Tables 23 to 26 below list the movement amount and the values corresponding to the conditional expression (1) above of the second to fourth lens units Gr2 to Gr4 at the wide-angle end ›W(D)!, at the midpoint ›M(D)!, and at the telephoto end ›T(D)! during focusing (from the infinite-shooting-distance state to the closest-shooting-distance state, shooting distance=0.25 m) of the embodiments 8 to 11.

FIGS. 27, 29, 31, and 33 are lens construction diagrams corresponding to the embodiments 8, 9, 10, and 11, respectively. Each figure shows the lens arrangements in the closest-shooting-distance state ›W(D)! at the wide-angle end. FIGS. 28A to 28I, 30A to 30I, 32A to 32I, and 34A to 34I show aberration curves of the embodiments 8 to 11, respectively, in the closest-shooting-distance state, illustrating aberrations (FIGS. 28A to 28C, 30A to 30C, 32A to 32C, and 34A to 34C) at the wide-angle end ›W(D)!, aberrations (FIGS. 28D to 28F, 30D to 30F, 32D to 32F, and 34D to 34F) at the midpoint ›M(D)!, and aberrations (FIGS. 28G to 28I, 30G to 30I, 32G to 321, and 34G to 34I) at the telephoto end ›T(D)!.

FIG. 35A shows the same state as in FIG. 25. FIGS. 35B and 35C show the states after zooming from the state of FIG. 35A. FIG. 35B shows the midpoint state, and FIG. 35C shows the telephoto state. The states shown in FIGS. 35A to 35C are common to the embodiments 8 to 11.

FIGS. 36A to 36C show the focusing states of the embodiment 8. FIGS. 37A to 37C show the focusing states of the embodiment 9. Moreover, FIGS. 38A to 38C show the focusing states of the embodiment 10. Similarly, FIGS. 39A to 39C show the focusing states of the embodiment 11. FIGS. 36A, 37A, 38A, and 39A each show the states after focusing from the state of FIG. 35A; FIGS. 36B, 37B, 38B, and 39B each show the states after focusing from the state of FIG. 35B; FIGS. 36C, 37C, 38C, and 39C each show the states after focusing from the state of FIG. 35C.

FIGS. 27, 29, 31, and 33 correspond to FIGS. 36A, 37A, 38A, and 39A, respectively.

As described above, according to the present invention, it is possible to realize a zoom lens system that offers a shorter closest shooting distance, compactness, and a high degree of optical performance at the same time.