Electronic image pickup system

[0001] This application claims benefits of Japanese Application No. 2001-142948 filed in Japan on May 14, 2001, the contents of which are incorporated by this reference.

[0002] The present invention relates generally to a slim electronic image pickup system comprising an optical path-bending zoom optical system, and particularly to an image pickup system inclusive of video cameras or digital cameras, the depth dimension of which is reduced by contriving an optical system portion thereof, e.g., a zoom lens.

[0003] In recent years, digital cameras (electronic cameras) have received attention as cameras of the next generation, an alternative to silver-salt 35 mm-film (usually called Leica format) cameras. Currently available digital cameras are broken down into some categories in wide ranges from the high-end type for commercial use to the portable low-end type.

[0004] In view of the portable low-end type category in particular, the primary object of the present invention is to provide the technology for implementing video or digital cameras whose depth dimension is reduced while ensuring high image quality.

[0005] The gravest bottleneck in making the depth dimension of cameras thin is the thickness of an optical system, especially a zoom lens from the surface located nearest to the object side to the image pickup plane. To make use of a collapsible lens mount that allows the optical system to be taken out of a camera body for phototaking and received therein for carrying now becomes mainstream. However, the thickness of an optical system received in a collapsible lens mount varies largely with the lens type or filter used. Especially in the case of a so-called precedent type zoom lens wherein a lens group having positive refracting power is positioned nearest to its object side, the thickness of each lens element and dead space are too large to set such requirements as zoom ratios and F-numbers at high values; in other words, the optical system does not become slime as expected, even upon received in the lens mount (JP-A 11-258507). A precedent type zoom lens, especially of two or three-group construction is advantageous in this regard. However, this type zoom lens, too, does not become slim upon received in a collapsible lens mount, even when the lens positioned nearest to the object side is formed of a positive lens (JP-A 11-52246), because the lens groups are composed of an increased number of lens elements, and the thickness of lens elements is large.

[0006] Among zoom lenses known so far in the art, those set forth typically in JP-A's 11-194274, 11-287953 and 2000-9997 are suitable for use with electronic image pickup systems with improved image-formation capabilities including zoom ratios, field angles and F-numbers, and may possibly be reduced in thickness upon received in collapsible lens mounts.

[0007] To make the first lens group thin, it is preferable to make the entrance pupil position shallow; however, the magnification of the second lens group must be increased to this end. For this reason, some considerable load is applied on the second lens group. Thus, it is not only difficult to make the second lens group itself thin but it is also difficult to make correction for aberrations. In addition, the influence of production errors grows. Thickness and size reductions may be achieved by making the size of an image pickup device small. To ensure the same number of pixels, however, the pixel pitch must be diminished and insufficient sensitivity must be covered by the optical system. The same goes true for the influence of diffraction.

[0008] To obtain a camera body whose depth dimension is reduced, a rear focusing mode wherein the rear lens group is moved for focusing is effective in view of the layout of an associated driving system. It is then required to single out an optical system less susceptible to aberration fluctuations upon rear focusing. Alternatively, such thickness reductions may be achieved by bending the optical path of an optical system with a mirror or the like; however, some considerable restrictions are imposed on the zooming movement of lenses because of the space for such optical path bending.

[0009] In view of such problems with the prior art as referred to above, the primary object of the present invention is to provide an electronic image pickup system with extremely diminished depth dimension, which makes use of a rear focus type zoom lens wherein the optical path (optical axis) of an optical system is bent with a reflecting optical element such as a mirror, and restrictive conditions for the zooming movement of a moving lens group can be substantially eliminated while maintaining high specification requirements and improved performance.

[0010] According to the present invention, the aforesaid object is accomplished by the provision of an electronic image pickup system, characterized by comprising an optical path-bending zoom optical system comprising at least one lens group that moves only toward an object side of said optical system for zooming from a wide-angle end to a telephoto end of said optical system and at least one reflecting optical element for bending an optical path, which element is located between said object side of said optical system and a lens included in all lens groups movable during zooming and located nearest to said object side of said optical system, and an electronic image pickup device disposed on an image side of said optical system.

[0011] Why the aforesaid arrangement is used in the present invention, and how it works is now explained.

[0012] In the present invention, there is used an optical path-bending zoom optical system comprising at least one lens group that moves only toward the object side of said optical system for zooming from a wide-angle end to a telephoto end of said optical system and at least one reflecting optical element for bending an optical path, which element is located between said object side of said optical system and a lens included in all lens groups movable during zooming and located nearest to said object side of said optical system. To direct the entrance surface of the lens system toward the object side and reduce the depth dimension thereof, it is preferable that the optical path is bent at a position of a phototaking optical system which is as close to the object side as possible and at an air separation where the height of light rays is low. To simplify the driving system for zooming and focusing purposes, the moving lens group(s) is preferably located at an image side position with respect to the bending position. To reduce bending space as much as possible, it is preferable that the composite or combined focal length of a partial system from the lens disposed nearest to the object side, at which the bending portion exists, to just before the lens group that moves during zooming, is negative, because the heights of all light rays contributing to the formation of images in the vicinity of the bending position should preferably be low.

[0013] Specifically, one lens arrangement well fit for the bending zoom optical system is of the type that comprises, in order from its object side, a 1-1st lens group comprising a negative lens group and a reflecting optical element for bending an optical path, a 1-2nd lens group comprising one positive lens and a second lens group having positive refracting power, wherein for zooming from the wide-angle end to the telephoto end of the arrangement, the second lens group moves only toward the object side of the arrangement.

[0014] Another lens arrangement well suitable for the bending zoom optical system is of the type that comprises, in order from its object side, a 1-1st lens group comprising a prism that is a reflecting optical element for bending an optical path, wherein at least one of an entrance surface and an exit surface is defined by a concave surface, a 1-2nd lens group comprising one positive lens and a second lens group having positive refracting power, wherein for zooming form the wide-angle end to the telephoto end of the arrangement, the second lens group moves monotonously toward the object side of the arrangement.

[0015] In either type, it is preferable that an axial distance d, as calculated on an air basis, from a refracting surface just before the reflecting surface of the reflecting optical element to a refracting surface just after the reflecting surface should satisfy the following condition (a):

[0016] where L is the diagonal length of an effective image pickup area (in a substantially rectangular form) on the electronic image pickup device.

[0017] As the upper limit of 2.1 to this condition (a) is exceeded, the optical system becomes too large. As the lower limit of 0.5 is not reached, a light beam that contributes to the imaging of the perimeter of an image does not satisfactorily arrive at the image plane or ghosts are likely to occur.

[0018] It is noted that when the field angle in the optical path-bending direction is in the range of 253, condition (a) should preferably be reduced down to the following condition (a-1), and when it is in the range of about 193, condition (a) should preferably be reduced down to the following condition (a-2).

[0019] More preferably,

[0020] In either type, the profile of paraxial refracting power may be properly determined even when surfaces other than a planar surface are used for the reflecting surface. Preferably, however, a control system that allows the shape of the reflecting surface to be freely transformed is provided to make up a variable-shape mirror that corrects fluctuations of focal position and aberrations with zooming, and is of controllable shape for focusing or zooming purposes.

[0021] Alternatively, the reflecting optical element may be constructed as by cementing a planoconcave lens to a planar portion of the prism. To reconcile the level of correction of distortion well with the target size of the electronic image pickup system, it is acceptable to add a positive lens of weak power to the surface of the reflecting optical element located nearest to the object side. In this case, the 1-2nd lens group may be dispensed with.

[0022] Preferably in each of the two zoom types, the final lens group should be made up of a single lens having an aspheric surface. This is very effective for correction of off-axial aberrations such as distortions, astigmatisms and comas. This lens serves to cancel out aberrations produced at portions of the optical system, which are present on the object side with respect thereto; as the lens moves for focusing or other purposes, aberrations get out of balance. Thus, it is preferable to fix the final lens group.

[0023] Focusing should preferably be carried out with the second lens group and, if any, the subsequent lens group(s) save the final lens group, because the first lens group is provided for bending the optical path and so is not appropriate for any focusing group. It is particularly preferable to carry out focusing with the second lens group as counted from the final lens group toward the object side, because that lens group is less vulnerable to focal length and aberration fluctuations. When, in this case, the optical system is focused on a nearby object, such second lens group is moved out. For focusing, it is then preferable that the optical axis air separation D_FT between the second lens group and the third lens group as counted from the final lens group toward the object side, upon focused on an infinite-distance object point at the telephoto end, satisfies the following condition (b).

[0024] Here f_T is the focal length of the zoom optical system upon focused on an infinite-distance object point at the telephoto end.

[0025] As the upper limit of 1.5 to condition (b) is exceeded, it is difficult to ensure any desired zoom ratio, and as the lower limit of 0.1 is not reached, it is impossible to allow any focusable distance.

[0026] More preferably,

[0027] Even more preferably,

[0028] Each of the aforesaid two zoom types should preferably comprise an additional or third lens group located on the image side of the second lens group and having positive refracting power, so that upon zooming from the wide-angle end to the telephoto end, the second and third lens groups move with a change in the relative spacing between them. With this zooming mode, it is possible to make the zoom ratio of the optical system high while its focal position upon zooming is corrected by taking advantage of space.

[0029] Preferably in that case, the ratio between the amounts of movement M₂ and M₃ of the second and third lens groups upon zooming from the wide-angle end to the telephoto end of the optical system when focused on a point at infinity should satisfy the following range:

[0030] As the upper limit of 2.0 to condition (c) is exceeded, it is impossible to ensure any satisfactory zoom ratio or focusable distance range. As the lower limit of 0.5 is not reached, it is again impossible to ensure any satisfactory zoom ratio.

[0031] More preferably,

[0032] Even more preferably,

[0033] Preferable in each of the aforesaid two zoom types, the first lens group (the combined 1-1st and 1-2nd system) should remain fixed upon zooming or focusing, because it is an optical path-bending system that is difficult to move for mechanical reasons. It is here noted that while the 1-1st lens group is fixed upon zooming, the 1-2nd lens group may remain movable because of being relatively easy to move. Preferably in this case, the 1-2nd lens group should be designed to move in an orbit convex toward the image side. It is also preferable that the 1-2nd lens group comprises, in order from its object side, two lenses, a negative and a positive or, alternatively, one positive lens for the purpose of correcting off-axis aberrations such as chromatic aberrations and distortions.

[0034] Furthermore, if any one of such structural limitations as mentioned below is added to the bending zoom lens system, it is then possible to better its specifications and performance and simplify its construction, resulting in additional contributions to thickness reductions of the associated image pickup systems.

[0035] Limitation 1:

[0036] In the 1-1st lens group, the negative lens group located on the object side with respect to the reflecting optical element for bending the optical path comprises only one negative lens convex on its object side. With this arrangement, it is possible to minimize the depth dimension of the optical system while the desired field angle is maintained.

[0037] Limitation 2:

[0038] In that case, it is of significance that the negative lens has some power. In other words, the power ratio between the 1-1st lens group and the 1-2nd lens group should preferably satisfy:

[0039] where f₁₁ is the focal length of the 1-1st lens group and f₁₂ is the focal length of the 1-2nd lens group. Any deviation from the upper and lower limits of 1.9 and 0.8 makes the bending optical element likely to become large.

[0040] More preferably,

[0041] Even more preferably,

[0042] Limitation 3:

[0043] One of the second and third lens groups comprises a single lens, and the other comprises at least a concave lens.

[0044] The second and third lens groups move in approximately the same direction while the relative spacing between them changes slightly so that they can share the common use of a narrow space for zooming while the focal position is kept constant. Another merit is that correction of chromatic aberrations is not necessarily brought to completion for each lens group. In short, chromatic aberrations at the second lens group can be corrected separately from those at the third lens group, so that either one can be composed of a single lens, resulting in some contribution to the size and weight reductions of the optical system.

[0045] Limitation 4:

[0046] To reduce the change in the relative spacing between the second and the third lens group as much as possible, zooming should preferably be carried out at the magnification of the combined system of the second and subsequent lens groups, which is around 1. To this end, it is desired to satisfy the following condition at the telephoto end:

[0047] Here _Rt is the combined magnification of the second and subsequent lens groups at the telephoto end (upon focused on an object point at infinity).

[0048] Any deviation from the upper and lower limits of 2.1 and 0.7 to this condition incurs an increase in the amount of change in the relative spacing between the second and the third lens group.

[0049] More preferably,

[0050] Even more preferably,

[0051] The present invention also provides an electronic image pickup system, characterized by comprising:

[0052] an optical path-bending zoom optical system comprising at least one lens group that moves only toward its object side upon zooming from the wide-angle end to the telephoto end of the optical system and at least one reflecting optical element for, upon zooming, bending an optical path toward the object side with respect to the lens included in all movable lens groups and located nearest to the object side,

[0053] said optical path being defined by an entrance surface and an exit surface, at least one of which has a curvature, and

[0054] an electronic image pickup device located on the image side of said optical system.

[0055] Thus, if the reflecting optical element (prism) for bending the optical path is allowed to have refracting power, it is then possible to diminish the number of lens elements, making contributions to size reductions or cost reductions.

[0056] In this case, the reflecting optical element for bending the optical path may be located nearest to the object side of the optical path-bending zooming optical system.

[0057] Thus, if the optical path-bending element is located as near to the object side as possible, it is then possible to diminish the depth dimension of the electronic image pickup system.

[0058] Furthermore, the entrance surface of the reflecting optical element for bending the optical path may be directed toward the object side of the zoom optical system.

[0059] According to one embodiment of the present invention, there is provided a slim electronic image pickup system constructed using a zoom optical system comprising, in order from its object side, a negative meniscus lens and an optical path-bending prism. If the optical path-bending prism is designed to have an entrance surface with negative refracting power, it is then possible to make the depth dimension of the electronic image pickup system by far smaller, because that negative meniscus lens can be dispensed with.

[0060] In that case, the entrance surface of the reflecting optical element for bending the optical path may be defined by an aspheric surface.

[0061] The axial curvature of the entrance surface having a negative value (the entrance surface being concave on the object side) is unfavorable in consideration of correction of off-axis aberrations such as distortions. With the introduction of the aspheric surface, however, such aberrations can be well corrected.

[0062] Furthermore, the exit surface of the reflecting optical element for bending the optical path may be defined by a planar surface.

[0063] It is here noted that when an aspheric surface is applied to the entrance surface as mentioned above, it is difficult to ensure any desired decentration accuracy between that surface and the exit surface. However, if another surface (exit surface) is defined by a planar surface, it is then possible to slacken off demand for decentration accuracy between both surfaces.

[0064] The lens group that moves only toward the object side upon zooming from the wide-angle end to the telephoto end is made up of two positive lenses and at least one negative lens. It is then acceptable that at least each positive lens and the negative lens are cemented together.

[0065] In the lens group that moves only toward the object side upon zooming form the wide-angle end to the telephoto end, there is a tendency for aberrations to deteriorate largely due to relative decentration between the positive lens and the negative lens. It is thus preferable that the positive and the negative lens are cemented to the greatest extent practicable.

[0066] The lens group that moves only toward the object side upon zooming from the wide-angle end to the telephoto end is made up of two positive lenses and at least one negative lens. It is then acceptable that at least one positive lens and the negative lens are cemented together.

[0067] Thus, the lens group that moves only toward the object side upon zooming from the wide-angle end to the telephoto end should comprise at least two positive lenses and at least one negative lens, at least three in all.

[0068] Next, how and why the thickness of filters is reduced is now explained. In an electronic image pickup system, an infrared absorption filter having a certain thickness is usually inserted between an image pickup device and its object side and positioned nearer to the object side, so that the incidence of infrared light on the image pickup plane is prevented. Here consider the case where this filter is replaced by a coating devoid of thickness. In addition to the fact that the system becomes thin as a matter of course, there are spillover effects. When a near-infrared sharp cut coat having a transmittance of at least 80% at 600 nm and a transmittance of up to 10% at 700 nm is introduced between an image pickup device in the rear of the zoom lens system and the object side of the system and nearer to the object side, the transmittance on the red side is relatively higher that that of the absorption type, so that the tendency of bluish purple to turn into magentaa defect of a complementary mosaic filter-inserted CCDis diminished by gain control and there can be obtained color reproduction comparable to that by a CCD having a primary colors filter. On the other hand, a complementary filter is higher in substantial sensitivity and more favorable in resolution than a primary colors filter-inserted CCD due to its high transmitted energy, and provides a great merit when used in combination with a small-size CCD. Regarding an optical low-pass filter that is another filter, too, its total thickness, t_LPF, should preferably comply with the following condition:

[0069] Here a is the horizontal pixel pitch (in m) of the electronic image pickup device.

[0070] Reducing the thickness of the optical low-pass filter, too, is effective for making the thickness of the zoom lens upon received in the lens mount; however, this is generally not preferred because the moir preventive effect becomes slender. On the other hand, as the pixel pitch becomes small, the contrast of frequency components greater than Nyquist criterion decreases under the influence of diffraction of an image-formation lens and, consequently, the decrease in the moir preventive effect is more or less acceptable. For instance, it is known that when three different filters having crystallographic axes in directions where upon projected onto the image plane, the azimuth angle is horizontal (0) and 45 are used while they are put one upon another, some moir preventive effect is obtainable. According to the specifications known to make the filter assembly thinnest, each filter is displaced by a m in the horizontal and by SQRT()*a m in the 45 directions. Here SQRT means a square root. The then filter thickness is approximately given by 12*SQRT()*a/5.88 (mm). This is the specification where the contrast is reduced down to zero at a frequency corresponding just to Nyquist criterion. At a thickness a few % to a few tens of % smaller than this, a little more contrast of the frequency corresponding to Nyquist criterion appears; however, this can be suppressed under the influence of the aforesaid diffraction.

[0071] In other filter embodiments where two filters are placed one upon another or one single filter is used, too, it is preferable to comply with condition (f). When the upper limit of 0.45a is exceeded, the optical low-pass filter becomes too thick, contrary to size reduction requirements. When the lower limit of 0.15a is not reached, moir removal becomes insufficient. In this condition, a should be 5 m or less.

[0072] When a is 4 m or less or where the optical low-pass filter is more susceptible to diffraction, it is preferable that

[0073] It is also acceptable that

[0074] when a is 4 m or greater,

[0075] 0.3a<t_LPF<0.4a provided that three filters are placed one upon another and a<5 m

[0076] 0.2a<t_LPF<0.28a provided that two filters are placed one upon another and a<5 m

[0077] 0.1a<t_LPF<0.16a provided that one filter is used and a<5 m

[0078] when a is 4 m or less,

[0079] 0.25a<t_LPF<0.37a provided that three filters are placed one upon another

[0080] 0.16a<t_LPF<0.25a provided that two filters are placed one upon another

[0081] 0.08a<t_LPF<0.14a provided that one filter is used

[0082] When an image pickup device having a small pixel pitch is used, there is degradation in image quality under the influence of diffraction effect by stop-down. In this case, the electronic image pickup system is designed in such a way as to have a plurality of apertures each of fixed aperture size, one of which can be inserted into any one of optical paths between the lens surface located nearest to the image side of the first lens group and the lens surface located nearest to the object side of the third lens group and can be replaced with another as well, so that illuminance on the image plane can be adjusted. Then, media whose transmittances with respect to 550 nm are different but less than 80% are filled in some of the plurality of apertures for light quantity control. Alternatively, when control is carried out in such a way as to provide a light quantity corresponding to such an F-number as given by a (m)/F-number<4.0, it is preferable to fill the apertures with medium whose transmittance with respect to 550 nm are different but less than 80%. In the range of the full-aperture value to values deviating from the aforesaid condition as an example, any medium is not used or dummy media having a transmittance of at least 91% with respect to 550 nm are used. In the range of the aforesaid condition, it is preferable to control the quantity of light with an ND filter or the like, rather than to decrease the diameter of the aperture stop to such an extent that the influence of diffraction appears.

[0083] Alternatively, it is acceptable to uniformly reduce the diameters of a plurality of apertures inversely with the F-numbers, so that optical low-pass filters having different frequency characteristics can be inserted in place of ND filters. As degradation by diffraction becomes worse with stop-down, it is desirable that the smaller the aperture diameter, the higher the frequency characteristics the optical low-pass filters have.

[0084] In order to slim down an electronic image pickup system, not only contrivances for an associated optical system but also contrivances for its mechanical mechanism and layouts are of importance. In particular, it is important to take advantage of the collapsible lens mount type wherein the optical system is received in the lens mount. For the lens arrangement of the present invention, it is preferable to make use of a specific collapsible lens mount type wherein the reflecting optical element already in the optical system body is relocated from the optical path in a separate space in the optical system body, and the lens groups that are located on the object side with respect to the reflecting optical element and move out of the optical system body during phototaking are received in the resulting space on the optical path.

[0085] This specific collapsible lens mount type may also be applied to an optical system having a lens arrangement other than that of the present invention, provided that it comprises, in order from its object side, a first lens group of negative power, a reflecting optical element for bending an optical path and a second lens group of positive power. The reflecting optical element is relocated from the optical path in a separate space in the optical system body, so that the first lens group is received in the resulting space on the optical path.

[0086] Preferably in this case, while the first lens group is received in the optical system body, the second lens group is shifted to the image side with respect to the position farthest away from the image plane at the time of phototaking. There is also a moving space for zooming or focusing subsequent to the second lens group. To make effective use of that space during lens reception or the like, the second lens is put down as close to the image side as possible and, if required, the reflecting optical element is shifted to the image side, so that the first lens group is received in place.

[0087] For instance, when the reflecting optical element is constructed of a reflecting mirror comprising a thin plate with a reflecting mirror coating applied thereon, the first lens group can be received in place with no need of any separate space, because the reflecting mirror is relocated vertically to the optical axis with the reflecting surface bent.

[0088] Besides, each of lenses other than the reflecting optical element may be tilted or shifted during lens reception, thereby creating some reception space.

[0089] When the prism is constructed of a solid outer shell with a liquid or the like filled therein, thickness reductions may be achieved by removing the liquid from inside.

[0090] It is noted that with an optical system using a reflecting optical element, the following embodiments are feasible.

[0091] The best embodiment is a TTL single-lens reflecting optical system fused with a Porro prism type finder.

[0092] In one typical embodiment of this optical system, between a phototaking optical system including a reflecting optical element and an image pickup device there is interposed a second reflecting surface for splitting (in time division, amplitude division or any other modes) an optical path toward a side nearly at right angles with a plane including an optical axis before and after reflection at the reflecting optical element. A third reflecting surface is disposed along the opposite side, with the normal lying in much the same plane with respect to the normal to the second reflecting surface and nearly at right angles therewith. Furthermore, a fourth reflecting surface is disposed in such a way that an optical path after reflection thereat runs parallel with the optical axis of the entrance side of the phototaking optical system. This makes a great deal of contribution to the thickness reductions of a camera.

[0093] In the second embodiment wherein the reflecting optical element and an optical system on the object side with respect thereto is designed to be rotatable with respect to the vicinity of the entrance pupil of a phototaking optical system or the like, it is possible to change the phototaking direction. Alternatively, optical prevention of camera movements is possible.

[0094] Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

[0095] The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

[0096] FIGS. 1(a) to 1(c) are sections in schematic illustrative of Example 1 of the optical path-bending zoom optical system used with the electronic image pickup system of the invention at the telephoto end (a), intermediate state (b) and wide-angle end (c) when the optical path-bending zoom optical system is focused on an object point at infinity.

[0097] FIGS. 2(a) to 2(c) are sections in schematic illustrative of Example 2 of the optical path bending-zoom optical system, similar to FIGS. 1(a) to 1(c).

[0098] FIGS. 3(a) to 3(c) are sections in schematic illustrative of Example 3 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0099] FIGS. 4(a) to 4(c) are sections in schematic illustrative of Example 4 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0100] FIGS. 5(a) to 5(c) are sections in schematic illustrative of Example 5 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0101] FIGS. 6(a) to 6(c) are sections in schematic illustrative of Example 6 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0102] FIGS. 7(a) to 7(c) are sections in schematic illustrative of Example 7 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0103] FIGS. 8(a) to 8(c) are sections in schematic illustrative of Example 8 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0104] FIGS. 9(a) to 9(c) are sections in schematic illustrative of Example 9 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0105] FIGS. 10(a) to 10(c) are sections in schematic illustrative of Example 10 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0106] FIGS. 11(a) to 11(c) are sections in schematic illustrative of Example 11 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0107] FIGS. 12(a) to 12(c) are sections in schematic illustrative of Example 12 of the optical path-bending zoom optical system, similar to FIGS. 1(a) to 1(c).

[0108] FIGS. 13(a) to 13(c) are aberration diagrams of Example 1 upon focused on an object point at infinity.

[0109] FIGS. 14(a) to 14(c) are aberration diagrams of Example 12 upon focused on an object point at infinity.

[0110] FIGS. 15(a) and 15(b) are conceptual schematics illustrative of one embodiment of how to receive the optical path bending-zoom optical system of the invention in place.

[0111] FIG. 16 is a conceptual schematic illustrative of one embodiment of how to receive the optical system body in place when the reflecting optical element for bending an optical path is constructed of a mirror.

[0112] FIG. 17 is a conceptual schematic illustrative of another embodiment of how to receive the optical system in place when the reflecting optical element for bending an optical path is constructed of a mirror.

[0113] FIGS. 18(a) and 18(b) are conceptual schematics illustrative of one embodiment of how to receive the optical system in place when the reflecting optical element for bending an optical path is constructed of a liquid or transformable prism.

[0114] FIG. 19 is a conceptual schematic illustrative of how to carry out focusing when the reflecting optical element for bending an optical path is constructed of a variable-shape mirror.

[0115] FIG. 20 is a conceptual schematic illustrative of the surface shape of a variable-shape mirror.

[0116] FIG. 21 is a conceptual schematic illustrative of how to correct camera movements when the reflecting optical element for bending an optical path is constructed of a variable-shape mirror.

[0117] FIG. 22 is a conceptual schematic illustrative of how to split a finder optical path from the optical path-bending zoom optical system.

[0118] FIG. 23 is a diagram indicative of the transmittance characteristics of one example of the near-infrared sharp cut coat.

[0119] FIG. 24 is a diagram indicative of the transmittance characteristics of one example of the color filter located on the exit surface side of the low-pass filter.

[0120] FIG. 25 is a schematic illustrative of how the color filter elements are arranged in the complementary mosaic filter.

[0121] FIG. 26 is a diagram indicative of one example of the wavelength characteristics of the complementary mosaic filter.

[0122] FIG. 27 is a detailed perspective view illustrative of one example of the aperture stop portion in each example.

[0123] FIGS. 28(a) and 28(b) are illustrative in detail of another example of the aperture stop in each example.

[0124] FIG. 29 is a front perspective schematic illustrative of the outside shape of a digital camera with the inventive optical path-bending zoom optical system built therein.

[0125] FIG. 30 is a rear perspective schematic of the digital camera of FIG. 29.

[0126] FIG. 31 is a sectional schematic of the digital camera of FIG. 29.

[0127] FIG. 32 is a front perspective view of an uncovered personal computer in which the inventive optical path-bending zoom optical system is built in the form of an objective optical system.

[0128] FIG. 33 is a sectional schematic of a phototaking optical system for a personal computer.

[0129] FIG. 34 is a side view of FIG. 32.

[0130] FIGS. 35(a) to 35(c) are a front and a side view of a cellular phone with the inventive optical path-bending zoom optical system built in as an objective optical system, and a sectional view of a phototaking optical system therefore, respectively.

[0131] Examples 1 to 12 of the optical path-bending zoom optical system used with the electronic image pickup system of the invention are now explained. Sectional lens configurations of these examples at the telephoto end (a), intermediate state (b) and wide-angle end (c) upon focused on an object point at infinity are shown in FIGS. 1 through 12 wherein G1 represents a first lens group, G1-1 a 1-1st lens group, G1-2 a 1-2nd lens group, G2 a second lens group, G3 a third lens group, G4 a fourth lens group, G5 a fifth lens group, P an optical path-bending prism, S an aperture stop (in an independent case), IF a near infrared cut filter, IC a near infrared cut coat surface, LF a low-pass filter, CG a cover glass for an electronic image pickup device CCD, and I the image plane of CCD. The near infrared cut filter IF and low-pass filter LF or the near infrared cut coat surface IC, low-pass filter LF and cover glass CG, located in order from the object side of the zoom optical system, are fixedly provided between the final lens group and the image plane I.

[0132] As shown in FIG. 1, Example 1 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of an optical path-bending prism P equivalent to a double-concave negative lens, a 1-2nd lens group G1-2 consisting of a double-convex positive lens, a second lens group G1 consisting of an aperture stop and a double-convex positive lens, a third lens group G3 consisting of a doublet composed of a double-convex positive lens and a double-concave negative lens and a double-convex positive lens, a fourth lens group G4 consisting of a negative meniscus lens convex on its object side, and a fifth lens group G5 consisting of a double-convex positive lens. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side while the spacing between them becomes wide and then narrow, and the fourth lens group G4 and the third lens group G3 move toward the object side while the spacing between them becomes wide.

[0133] Four aspheric surfaces are used, one at the object-side surface of the double-convex positive lens in the 1-2nd lens group G1-2, one at the object-side surface of the double-convex positive lens in the second lens group G2, one at the image-side surface of the negative meniscus lens in the fourth lens group G4, and one at the image-side surface of the double-convex positive lens in the fifth lens group G5.

[0134] As shown in FIG. 2, Example 2 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group consisting of an optical path bending prism P equivalent to a double-concave negative lens, a 1-2nd lens group consisting of a double-convex positive lens, an independently moving aperture stop S, a second lens group G2 consisting of a double-convex positive lens, a positive meniscus lens convex on its object side and a negative meniscus lens convex on its object side, a third lens group G3 consisting of a double-convex positive lens and a negative meniscus lens convex on its image side, and a fourth lens group G4 consisting of a positive meniscus lens convex on its object side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group move toward the object side while the spacing between them becomes wide. The aperture stop S located between the 1-2nd lens group 1-2 and the second lens group G2, too, moves toward the object side while the spacing between the 1-2nd lens group G1-2 and the fourth lens group G4 becomes narrow.

[0135] Three aspheric surfaces are used, one at the object-side surface of the double-convex positive lens in the 1-2nd lens group G1-2, one at the surface of the second lens group G2 located nearest to its object side, and one at the object-side surface of the positive meniscus lens in the fourth lens group G4.

[0136] As shown in FIG. 3, Example 3 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group G1-2 consisting of a double-concave negative lens and a double-convex positive lens, a second lens group G2 consisting of an aperture stop and a double-convex positive lens, a third lens group G3 consisting of a double-convex positive lens, a negative meniscus lens convex on its object side, a double-convex positive lens and a negative meniscus lens convex on its image side, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow.

[0137] Three aspheric surface are used, one at the object side-surface of the double-convex positive lens in the 1-2nd group G1-2, one at the surface of the third lens group G3 located nearest to its object side, and one at the object side-surface of the positive meniscus lens in the fourth lens group G4.

[0138] As shown in FIG. 4, Example 4 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group G1-2 consisting of a double-concave negative lens and a double-convex positive lens, a second lens group G2 consisting of an aperture stop, a double-convex positive lens, a double-convex positive lens and a negative meniscus lens convex on its object side, a third lens group G3 consisting of a positive meniscus lens convex on its object side, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow.

[0139] Three aspheric surfaces are used, one at the object-side surface of the double-convex positive lens in the 1-2nd lens group G1-2, one at the object-side surface of the double-convex positive lens located after the stop in the second lens group G2, and one at the object-side surface of the positive meniscus lens in the second lens group G4.

[0140] As shown in FIG. 5, Example 5 is directed to an optical path-bending zoom optical system made up of a first lens group G1 consisting of a positive meniscus lens convex on its object side, a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a second lens group G2 consisting of an aperture stop and a double-convex positive lens, a third lens group G3 consisting of a doublet consisting of a double-convex positive lens and a double-concave negative lens and a double-convex positive lens, a fourth lens group G4 consisting of a negative meniscus lens convex on its object side, and a fifth lens group G5 consisting of a positive meniscus lens convex on its object side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow, the third lens group G3 and the fourth lens group G4 move toward the object side while the spacing between them becomes wide, and the fifth lens group moves slightly toward the image side of the zoom optical system.

[0141] Four aspheric surfaces are used, one at the image-side surface of the double-convex positive lens in the first lens group G1, one at the object side-surface of the double-convex positive lens in the second lens group G2, one at the image side-surface of the negative meniscus lens in the fourth lens group G4 and one at the image side-surface of the positive meniscus lens in the fifth lens group G5.

[0142] As shown in FIG. 6, Example 6 is directed to an optical path-bending zoom optical system made up of a first lens group G1 consisting of a double-convex positive lens, a double-concave negative lens and an optical path bending prism P equivalent to a plane-parallel plate, a second lens group G2 consisting of an aperture stop and a doublet consisting of a double-convex positive lens and a negative meniscus lens convex on its image side, a third lens group G3 consisting of a negative meniscus lens convex on its object side, and a fourth lens group G4 consisting of a double-convex positive lens. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide, and the fourth lens group G4 moves slightly toward the object side on the telephoto side while it moves in a convex orbit toward the image side of the zoom lens optical system.

[0143] Three aspheric surfaces are used, one at the object side-surface of the double-concave negative lens in the first lens group G1, one at the surface of the second lens group G2 located nearest to its object side and one at the image side-surface of the negative meniscus lens in the third lens group G3.

[0144] As shown in FIG. 7, Example 7 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group G1-2 consisting of a double-concave positive lens and a double-convex positive lens, a second lens group G2 consisting of an aperture stop, a double-convex positive lens, a doublet composed of a double-convex positive lens and a negative meniscus lens convex on its image side, a third lens group G3 consisting of a positive meniscus lens convex on its image side, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow.

[0145] Three aspheric surfaces are used, one at the image side-surface of the negative meniscus lens in the 1-1st lens group G1-1, one at the surface of the second lens group G2 located nearest to the object side and one at the object side-surface of the positive meniscus lens in the fourth lens group G4.

[0146] As shown in FIG. 8, Example 8 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group G1-2 consisting of a double-concave negative lens and a positive meniscus lens convex on its object side, a second lens group G2 consisting of an aperture stop, a double-convex positive lens and a doublet composed of a double-convex positive lens and a double-concave negative lens, a third lens group G3 consisting of a positive meniscus lens convex on its image side, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow.

[0147] Three aspheric surfaces are used, one at the object side-surface of the negative meniscus lens in the 1-1st lens group G1-1, the surface of the second lens group G2 located nearest to its object side and one at the image side-surface of the positive meniscus lens in the fourth lens group G4.

[0148] As shown in FIG. 9, Example 9 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group G1-2 consisting of a negative meniscus lens convex on its object side and a positive meniscus lens convex on its object side, a second lens group G2 consisting of an aperture stop and a double-convex positive lens, a third lens group G3 consisting of a double-convex positive lens, a negative meniscus lens convex on its object side and a doublet composed of a double-convex positive lens and a double-concave negative lens, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side while the spacing between them becomes wide and then narrow.

[0149] Three aspheric surfaces are used, one at the image side-surface of the negative meniscus lens in the 1-2nd lens group G1-2, one at the surface of the third lens group G3 located nearest to its object side and one at the object side-surface of the positive meniscus lens in the fourth lens group G4.

[0150] As shown in FIG. 10, Example 10 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group G1-2 consisting of a negative meniscus lens convex on its object side and a positive meniscus lens convex on its object side, a second lens group G2 consisting of an aperture stop and a doublet composed of a double-convex positive lens and a negative meniscus lens convex on its image plane side, a third lens group G3 consisting of a positive meniscus lens convex on its object side, a negative meniscus lens convex on its object side and a doublet composed of a double-convex positive lens and a double-concave negative lens, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image plane side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom lens system while the spacing between them becomes wide and then narrow.

[0151] Three aspheric surfaces are used, one at the image plane side-surface of the negative meniscus lens in the 1-2nd lens group G1-2, one at the surface of the third lens group G3 located nearest to its object side and one at the object side-surface of the positive meniscus lens in the fourth lens group G4.

[0152] As shown in FIG. 11, Example 11 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of a negative meniscus lens convex on its object side and an optical path bending prism P equivalent to a plane-parallel plate, a 1-2nd lens group consisting of a negative meniscus lens convex on its object side and a positive meniscus lens convex on its object side, a second lens group G2 consisting of an aperture stop and a doublet composed of a double-convex positive lens and a negative meniscus lens convex on its image plane side, a third lens group G3 consisting of a positive meniscus lens convex on its object side and a doublet composed of a planoconvex positive lens and a planoconcave negative lens, and a fourth lens group G4 consisting of a double-convex positive lens. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow.

[0153] Three aspheric surfaces are used, one at the image plane side-surface of the negative meniscus lens in the 1-2nd lens group G1-2, one at the object side-surface of the positive meniscus lens in the third lens group G3 and one at the image plane side-surface of the double-convex positive lens in the fourth lens group G4.

[0154] As shown in FIG. 12, Example 12 is directed to an optical path-bending zoom optical system made up of a 1-1st lens group G1-1 consisting of an optical path bending prism P equivalent to a planoconcave negative lens, a 1-2nd lens group G1-2 consisting of a doublet composed of a negative meniscus lens concave on its object side and a positive meniscus lens concave on its object side, a second lens group G2 consisting of a positive meniscus lens convex on its object side and a negative meniscus lens convex on its object side, a third lens group G3 consisting of a double-convex positive lens, and a fourth lens group G4 consisting of a positive meniscus lens convex on its image plane side. For zooming from the wide-angle end to the telephoto end of the zoom optical system, the second lens group G2 and the third lens group G3 move toward the object side of the zoom optical system while the spacing between them becomes wide and then narrow.

[0155] Three aspheric surfaces are used, one at the object side-surface of the optical path bending prism P in the 1-1st lens group G1-1, one at the surface of the second lens group G2 located nearest to its object side and one at the image plane side-surface of the positive meniscus lens in the fourth lens group G4.

[0156] Set out below are the numerical data on each example. Symbols used hereinafter but not hereinbefore have the following meanings:

[0157] f: focal length of the zoom optical system

[0158] 2: field angle

[0159] F_NO: F-number

[0160] WE: wide-angle end

[0161] ST: standard or intermediate state

[0162] TE: telephoto end

[0163] r₁, r₂, . . . : radius of curvature of each lens element

[0164] d₁, d₂, . . . : spacing between the adjacent lens elements

[0165] n_d1, n_d2, . . . : d-line refractive index of each lens element

[0166] V_d1, V_d2, . . . : Abbe constant of each lens element

[0167] Here let x be an optical axis on condition that the direction of propagation of light is positive and y be a direction perpendicular to the optical axis. Then, aspheric configuration is given by

[0168] where r is a paraxial radius of curvature, K is a conical coefficient, and A₄, A₆, A₈ and A₁₀ are the fourth, sixth, eighth and tenth aspheric coefficients, respectively.

[0169]

r1 26.8147	d1 3.8000	nd1 1.73400	d1 51.47
r2 (Mirror)	d2 3.2000	nd2 1.73400	d2 51.47
r3 6.2254	d3 1.7202
r4 424.9864	d4 2.4297	nd3 1.84666	d3 23.78
(Aspheric)
r5 48.1247	d5 (Variable)
r6 (Stop)	d6 0.5000
r7 17.8731	d7 2.0000	nd4 1.58913	d4 61.26
(Aspheric)
r8 16.6911	d8 (Variable)
r9 7.9903	d9 6.2379	nd5 1.48749	d5 70.23
r10 14.7007	d10 0.8488	nd6 1.84666	d6 23.78
r11 7.0178	d11 1.1903
r12 11.2307	d12 1.6307	nd7 1.84666	d7 23.78
r13 24.5400	d13 (Variable)
r14 18.1763	d14 0.5000	nd8 1.84666	d8 23.78
r15 5.9110	d15 (Variable)
(Aspheric)
r16 14.1876	d16 3.0000	nd9 1.58913	d9 61.26
r17 7.1178	d17 0.5006
(Aspheric)
r18	d18 0.8000	nd10 1.51633	d10 64.14
r19	d19 1.8000	nd11 1.54771	d11 62.84
r20	d20 0.5000
r21	d21 0.5000	nd12 1.51633	d12 64.14
r22	d22 1.1914
r23
(Image Plane)
	Aspherical Coefficients
	4th surface
	K 0.0195
	A4 5.4111 104
	A6 2.1984 106
	A8 4.5957 107
	A10 1.0754 108
	7th surface
	K 5.8821
	A4 2.7575 104
	A6 5.8194 106
	A8 7.9649 107
	A10 3.4848 108
	15th surface
	K 3.6043
	A4 2.6150 103
	A6 8.5623 106
	A8 2.8972 106
	A10 1.5174 107
	17th surface
	K 0.8882
	A4 1.1140 103
	A6 8.5962 106
	A8 3.9677 107
	A10 3.1086 108
Zooming Data ()
	WE	ST	TE
	f (mm)	4.59000	8.95000	13.23000
	FNO	2.8316	3.8724	4.6438
	2 ()	65.5	34.0	23.0
	d5	12.93741	5.34873	2.00000
	d8	2.61607	2.85689	0.50000
	d13	1.09671	5.22639	10.38165
	d15	1.00016	4.21405	4.71724

[0170]

r1 129.7294	d1 4.5500	nd1 1.80400	d1 46.57
r2 (Mirror)	d2 4.0019	nd2 1.80400	d2 46.57
r3 5.3898	d3 1.6465
r4 30.0332	d4 1.4609	nd3 1.84666	d3 23.78
(Aspheric)
r5 35.8611	d5 (Variable)
r6 (Stop)	d6 (Variable)
r7 9.6063	d7 2.7296	nd4 1.48749	d4 70.23
(Aspheric)
r8 30.8421	d8 0.1469
r9 10.1172	d9 2.1277	nd5 1.69680	d5 55.53
r10 97.1974	d10 0.0500
r11 12.1982	d11 0.7949	nd6 1.84666	d6 23.78
r12 5.7271	d12 (Variable)
r13 14.2960	d13 4.0342	nd7 1.48749	d7 70.23
r14 15.7323	d14 0.1401
r15 18.5671	d15 1.1241	nd8 1.84666	d8 23.78
r16 29.8834	d16 (Variable)
r17 46.3841	d17 1.1752	nd9 1.58913	d9 61.26
(Aspheric)
r18 541.6142	d18 0.4453
r19	d19 0.8000	nd10 1.51633	d10 64.14
r20	d20 1.8000	nd11 1.54771	d11 62.84
r21	d21 0.5000
r22	d22 0.5000	nd12 1.51633	d12 64.14
r23	d23 1.2588
r24
(Image Plane)
	Aspherical Coefficients
	4th surface
	K 42.6072
	A4 4.5281 104
	A6 1.2752 108
	A8 2.9327 107
	A10 0
	7th surface
	K 0
	A4 2.9136 104
	A6 7.7511 107
	A8 2.4221 108
	A10 0
	17th surface
	K 0
	A4 8.0585 104
	A6 1.7583 105
	A8 1.1309 106
	A10 0
Zooming Data ()
	WE	ST	TE
	f (mm)	4.71141	7.84455	13.21508
	FNO	2.8000	3.6612	5.0650
	2 ()	67.8	41.2	24.8
	d5	10.20144	4.70557	1.12127
	d6	7.09024	5.59391	1.24849
	d12	3.08267	9.70509	10.04403
	d16	0.98577	1.28696	8.72623

[0171]

r1 22.0799	d1 0.7823	nd1 1.80400	d1 46.57
r2 7.0105	d2 1.1905
r3	d3 3.8000	nd2 1.80400	d2 46.57
r4 (Mirror)	d4 3.4483	nd3 1.80400	d3 46.57
r5	d5 0.4000
r6 43.4610	d6 0.7742	nd4 1.77250	d4 49.60
r7 9.6384	d7 0.6369
r8 19.1908	d8 1.6810	nd5 1.84666	d5 23.78
(Aspheric)
r9 40.1274	d9 (Variable)
r10 (Stop)	d10 0.5000
r11 85.1662	d11 1.5117	nd6 1.58913	d6 61.26
r12 18.3807	d12 (Variable)
r13 5.5347	d13 2.9473	nd7 1.48749	d7 70.23
(Aspheric)
r14 102.8346	d14 0.1500
r15 68.5128	d15 3.4582	nd8 1.84666	d8 23.78
r16 5.6774	d16 2.1376
r17 7.8453	d17 2.3148	nd9 1.60542	d9 45.99
r18 12.6010	d18 0.5441
r19 6.0465	d19 0.7255	nd10 1.61800	d10 63.33
r20 17.9513	d20 (Variable)
r21 17.2238	d21 1.4117	nd11 1.58913	d11 61.26
(Aspheric)
r22 9.8048	d22 0.5599
r23	d23 0.8000	nd12 1.51633	d12 64.14
r24	d24 1.8000	nd13 1.54771	d13 62.84
r25	d25 0.5000
r26	d26 0.5000	nd14 1.51633	d14 64.14
r27	d27 1.3641
r28
(Image Plane)
	Aspherical Coefficients
	8th surface
	K 1.5876
	A4 2.6616 104
	A6 3.3939 106
	A8 1.0023 107
	A10 0
	13th surface
	K 0
	A4 2.7230 104
	A6 5.7432 106
	A8 3.4301 107
	A10 0
	21th surface
	K 0
	A4 8.9975 104
	A6 1.8358 105
	A8 1.4143 106
	A10 0
Zooming Data ()
	WE	ST	TE
	f (mm)	4.60758	7.85021	13.40785
	FNO	2.8000	3.4489	4.6187
	2 ()	65.3	39.0	22.9
	d9	14.75212	6.67783	2.00000
	d12	0.67500	4.26744	1.54139
	d20	1.35767	6.03580	13.51290

[0172]

r1 29.0184	d1 0.7437	nd1 1.80400	d1 46.57
r2 7.3275	d2 1.3049
r3	d3 4.0000	nd2 1.80400	d2 46.57
r4 (Mirror)	d4 3.5133	nd3 1.80400	d3 46.57
r5	d5 0.3000
r6 31.2038	d6 0.7673	nd4 1.80400	d4 46.57
r7 15.2085	d7 1.5760
r8 33.1818	d8 1.5628	nd5 1.84666	d5 23.78
(Aspheric)
r9 29.4113	d9 (Variable)
r10 (Stop)	d10 0.5000
r11 20.3172	d11 1.9876	nd6 1.58913	d6 61.26
(Aspheric)
r12 14.3558	d12 0.1387
r13 7.0863	d13 2.5021	nd7 1.48749	d7 70.23
r14 521.1337	d14 0.0001
r15 217.6721	d15 5.9501	nd8 1.84666	d8 23.78
r16 4.5340	d16 (Variable)
r17 10.1062	d17 1.8686	nd9 1.60300	d9 65.44
r18 46.5940	d18 (Variable)
r19 22.5387	d19 2.3721	nd10 1.58913	d10 61.26
(Aspheric)
r20 5.8538	d20 0.4297
r21	d21 0.8000	nd11 1.51633	d11 64.14
r22	d22 0.8000	nd12 1.54771	d12 62.84
r23	d23 0.5000
r24	d24 0.5000	nd13 1.51633	d13 64.14
r25	d25 1.3824
r27
(Image Plane)
	Aspherical Coefficients
	8th surface
	K 1.9221
	A4 1.0674 104
	A6 7.5509 107
	A8 6.9692 108
	A10 0
	11th surface
	K 0
	A4 1.4582 104
	A6 4.2034 108
	A8 1.1204 108
	A10 0
	19th surface
	K 0
	A4 1.8514 103
	A6 6.5803 106
	A8 9.0686 107
	A10 0
Zooming Data ()
	WE	ST	TE
	f (mm)	4.65117	7.85007	13.29161
	FNO	2.5000	3.4944	4.8337
	2 ( )	68.4	41.7	24.7
	d9	13.35295	7.17214	2.00000
	d16	1.22323	4.89168	2.01917
	d18	0.94992	3.89804	12.56077

[0173]

r1 15.9959	d1 2.0000	nd1 1.84666	d1 23.78
r2 17.9366	d2 0.8000
(Aspheric)
r3 122.3665	d3 1.0000	nd2 1.72916	d2 54.68
r4 6.1500	d4 1.9000
r5	d5 4.1000	nd3 1.56883	d3 56.36
r6 (Mirror)	d6 3.9000	nd4 1.56883	d4 56.36
r7	d7 (Variable)
r8 (Stop)	d8 0.5928
r9 14.1418	d9 3.0000	nd5 1.80610	d5 40.92
(Aspheric)
r10 138.1914	d10 (Variable)
r11 9.2691	d11 3.2000	nd6 1.48749	d6 70.23
r12 18.4588	d12 1.0064	nd7 1.84666	d7 23.78
r13 7.4386	d13 0.5000
r14 9.1725	d14 2.4000	nd8 1.80518	d8 25.42
r15 16.4170	d15 (Variable)
r18 44.6119	d16 0.8000	nd9 1.84666	d9 23.78
r17 8.9511	d17 (Variable)
(Aspheric)
r18 11.2550	d18 2.6000	nd10 1.58913	d10 61.26
r19 673.2282	d19 (Variable)
(Aspheric)
r20	d20 1.5000	nd11 1.51633	d11 64.14
r21	d21 1.4400	nd12 1.54771	d12 62.84
r22	d22 0.8000
r23	d23 0.8000	nd13 1.51633	d13 64.14
r24	d24 1.0000
r25
(Image Plane)
	Aspherical Coefficients
	2nd surface
	K 0
	A4 2.1855 104
	A6 3.4923 107
	A8 0
	A 10 0
	9th surface
	K 5.1530
	A4 2.4340 104
	A6 7.4872 106
	A8 2.0515 107
	A10 1.0188 108
	17th surface
	K 3.7152
	A4 1.2209 103
	A6 1.7576 105
	A8 2.5810 106
	A10 1.2193 107
	19th surface
	K 1.4583
	A4 1.5578 104
	A6 1.1072 104
	A8 5.6481 107
	A10 8.6742 109
Zooming Data ()
	WE	ST	TE
	f (mm)	5.43000	10.61200	15.80000
	FNO	2.7116	3.7726	4.5293
	2 ()	63.5	35.7	24.5
	d7	13.12435	4.47821	0.50000
	d10	0.81880	1.71785	0.50000
	d15	0.60000	2.00387	4.09707
	d17	1.40000	8.20925	11.93740
	d19	2.71758	2.25155	1.62627

[0174]

r1 49.3427	d1 2.0000	nd1 1.84666	d1 23.78
r2 115.4656	d2 0.4000
r3 52.5304	d3 1.0000	nd2 1.69350	d2 53.21
(Aspheric)
r4 5.8428	d4 1.8000
r5	d5 4.0000	nd3 1.56883	d3 56.36
r6 (Mirror)	d6 3.8000	nd4 1.56883	d4 56.36
r7	d7 (Variable)
r8 (Stop)	d8 0.6000
r9 8.0295	d9 2.8000	nd5 1.69350	d5 53.21
(Aspheric)
r10 5.9145	d10 0.8000	nd6 1.80440	d6 39.59
r11 12.3640	d11 (Variable)
r12 26.8805	d12 0.8000	nd7 1.84666	d7 23.78
r13 7.1849	d13 (Variable)
(Aspheric)
r14 10.7803	d14 3.1000	nd8 1.48749	d8 70.23
r15 52.9481	d15 (Variable)
r16	d16 1.5000	nd9 1.51633	d9 64.14
r17	d17 1.4400	nd10 1.54771	d10 62.84
r18	d18 0.8000
r19	d19 0.8000	nd11 1.51633	d11 64.14
r20	d20 1.0000
r21
(Image Plane)
	Aspherical Coefficients
	3rd surface
	K 0
	A4 2.6048 104
	A6 3.2365 106
	A8 2.2913 108
	A10 0
	9th surface
	K 0
	A4 3.0615 104
	A6 2.0330 106
	A8 1.0403 107
	A10 0
	13th surface
	K 3.5241
	A4 1.8328 103
	A6 1.6164 105
	A8 3.5495 106
	A10 1.2410 107
Zooming Data ()
	WE	ST	TE
	f (mm)	5.38001	8.50001	13.45001
	FNO	3.0358	3.8702	4.5606
	2 ()	65.8	43.8	28.4
	d7	11.53527	6.15290	0.50000
	d11	2.10162	2.49863	3.68430
	d13	3.96820	9.09478	10.56416
	d15	1.75491	1.61369	4.61155

[0175]

r1 21.0760	d1 1.4000	nd1 1.74320	d1 49.34
r2 7.9352	d2 2.8000
(Aspheric)
r3	d3 6.5000	nd2 1.56883	d2 56.36
r4 (Mirror)	d4 6.0000	nd3 1.56883	d3 56.36
r5	d5 0.8000
r6 18.8610	d6 0.8000	nd4 1.72916	d4 54.68
r7 29.7460	d7 0.5273
r8 25.1850	d8 1.9000	nd5 1.84666	d5 23.78
r9 121.8149	d9 (Variable)
r10 (Stop)	d10 0.8000
r11 11.8772	d11 1.9992	nd6 1.49700	d6 81.54
(Aspheric)
r12 22.2117	d12 0.3000
r13 8.0295	d13 1.9997	nd7 1.48749	d7 70.23
r14 16.2855	d14 0.7997	nd8 1.64769	d8 33.79
r15 52.6732	d15 0.3000
r16 7.3242	d16 1.3308	nd9 1.84666	d9 23.78
r17 4.4772	d17 1.2000
r18 17.2769	d18 1.1317	nd10 1.80610	d10 40.92
r19 6.2199	d19 (Variable)
r20 9.0812	d20 2.0000	nd11 1.61800	d11 63.33
r21 19.8406	d21 (Variable)
r22 34.2139	d22 2.0000	nd12 1.58313	d12 59.38
(Aspheric)
r23 9.7728	d23 1.0032
r24	d25 1.4400	nd13 1.54771	d13 62.84
r25	d26 0.8000
r26	d27 0.8000	nd14 1.51633	d14 64.14
r27	d28 1.0003
r28
(Image Plane)
	Aspherical Coefficients
	2nd surface
	K 0
	A4 9.3483 105
	A6 1.4787 107
	A8 4.5620 108
	A10 0
	11th surface
	K 0
	A4 2.6863 104
	A6 1.0879 107
	A8 3.8711 109
	A10 0
	22nd surface
	K 0
	A4 4.8081 104
	A6 5.9535 106
	A8 1.6767 107
	A10 0
Zooming Data ()
	WE	ST	TE
	f (mm)	5.80000	9.17005	14.49992
	FNO	2.6880	3.4974	4.5402
	2 ()	60.8	40.1	25.4
	d9	14.10553	7.78994	2.48873
	d19	1.54225	5.16705	2.56297
	d21	2.32790	5.01801	12.92472

[0176]

r1 16.1825	d1 1.4000	nd1 1.80610	d1 40.92
(Aspheric)
r2 7.3872	d2 3.5000
r3	d3 6.5000	nd2 1.60311	d2 60.64
r4 (Mirror)	d4 6.0000	nd3 1.60311	d3 60.64
r5	d5 0.7950
r6 27.1461	d6 0.8000	nd4 1.72916	d4 54.68
r7 20.2982	d7 0.5273
r8 17.2255	d8 1.9000	nd5 1.84666	d5 23.78
r9 90.2451	d9 (Variable)
r10 (Stop)	d10 0.8000
r11 17.0416	d11 1.9965	nd6 1.56384	d6 60.67
(Aspheric)
r12 13.7245	d12 0.5000
r13 5.5039	d13 3.7857	nd7 1.48749	d7 70.23
r14 38.8943	d14 0.8000	nd8 1.69895	d8 30.13
r15 4.2611	d15 (Variable)
r16 16.8715	d16 2.0000	nd9 1.48749	d9 70.23
r17 96.4706	d17 (Variable)
r18 60.1937	d18 2.0000	nd10 1.56384	d10 60.67
r19 11.5463	d19 1.0039
(Aspheric)
r20	d20 1.4400	nd11 1.54771	d11 62.84
r21	d21 0.8000
r22	d22 0.8000	nd12 1.51633	d12 64.14
r23	d23 1.0021
r24
(Image Plane)
	Aspherical Coefficients
	1st surface
	K 0
	A4 5.1308 105
	A6 2.3428 107
	A8 3.7916 109
	A10 7.2819 1011
	11th surface
	K 0
	A4 1.6960 104
	A6 1.0587 106
	A8 5.6885 108
	A10 2.0816 1010
	19th surface
	K 0
	A4 2.9238 104
	A6 1.4179 105
	A8 6.7945 107
	A10 1.6439 108
Zooming Data ()
	WE	ST	TE
	f (mm)	5.80001	9.17026	14.49938
	FNO	2.6926	3.5230	4.5194
	2 ()	61.1	40.1	25.7
	d9	14.09978	8.00554	2.48873
	d15	2.47558	7.50212	3.24411
	d17	3.07729	4.13993	13.92316

[0177]

r1 21.2658	d1 1.0000	nd1 1.74100	d1 52.64
r2 8.6245	d2 3.3711
r3	d3 5.8400	nd2 1.80400	d2 46.57
r4 (Mirror)	d4 5.4952	nd3 1.80400	d3 46.57
r5	d5 0.3221
r6 300.0000	d6 1.0000	nd4 1.74320	d4 49.34
r7 15.3314	d7 0.5979
(Aspheric)
r8 15.8974	d8 1.4903	nd5 1.84666	d5 23.78
r9 43.0822	d9 (Variable)
r10 (Stop)	d10 0.6000
r11 63.9771	d11 1.3913	nd6 1.61800	d6 63.33
r12 23.2380	d12 (Variable)
r13 7.9674	d13 2.3478	nd7 1.48749	d7 70.23
(Aspheric)
r14 68.3182	d14 0.1000
r15 24.3652	d15 3.3012	nd8 1.84666	d8 23.78
r16 7.7880	d16 0.2484
r17 9.2912	d17 2.1349	nd9 1.72916	d9 54.68
r18 19.4929	d18 0.7000	nd10 1.53172	d10 48.84
r19 5.2999	d19 (Variable)
r20 22.5496	d20 2.5068	nd11 1.58913	d11 61.14
(Aspheric)
r21 6.5395	d21 1.0000
r22	d22 1.5000	nd12 1.51633	d12 64.14
r23	d23 1.4400	nd13 1.54771	d13 62.84
r24	d24 0.8000
r25	d25 0.8000	nd14 1.51633	d14 64.14
r26	d26 1.0894
r27
(Image Plane)
	Aspherical Coefficients
	7th surface
	K 0
	A4 6.9423 105
	A6 1.9216 107
	A8 2.3395 108
	A10 0
	13th surface
	K 0
	A4 2.1881 104
	A6 2.0288 106
	A8 7.6472 1010
	A10 0
	20th surface
	K 0
	A4 1.0095 103
	A6 3.4022 108
	A8 1.7165 107
	A10 0
Zooming Data ()
	WE	ST	TE
	f (mm)	5.52179	7.96811	15.98093
	FNO	2.4770	2.9873	4.5000
	2 ( )	64.5	44.7	22.7
	d9	17.73448	10.81643	2.00000
	d12	1.20000	3.80000	3.50000
	d19	2.60300	5.58623	15.86209

[0178]

r1 24.8917	d1 1.0000	nd1 1.74100	d1 52.64
r2 8.0792	d2 2.3760
r3	d3 5.2400	nd2 1.80400	d2 46.57
r4 (Mirror)	d4 5.0006	nd3 1.80400	d3 46.57
r5	d5 0.2922
r6 300.0000	d6 1.0000	nd4 1.74320	d4 49.34
r7 14.5213	d7 0.1000
(Aspheric)
r8 14.5896	d8 1.7517	nd5 1.84666	d5 23.78
r9 64.9869	d9 (Variable)
r10 (Stop)	d10 0.6000
r11 33.4595	d11 1.8985	nd6 1.61800	d6 63.33
r12 11.1499	d12 0.7000	nd7 1.80518	d7 25.42
r13 20.0542	d13 (Variable)
r14 10.2987	d14 2.0299	nd8 1.48749	d8 70.23
(Aspheric)
r15 18890.0000	d15 0.1000
r16 19.8062	d16 4.5045	nd9 1.84666	d9 23.78
r17 9.7836	d17 0.2000
r18 11.2175	d18 1.7598	nd10 1.72916	d10 54.68
r19 51.5183	d19 0.7000	nd11 1.53172	d11 48.84
r20 5.5430	d20 (Variable)
r21 23.0137	d21 1.9685	nd12 1.58913	d12 61.14
(Aspheric)
r22 7.0933	d22 1.0000
r23	d23 1.5000	nd13 1.51633	d13 64.14
r24	d24 1.4400	nd14 1.54771	d14 62.84
r25	d15 0.8000
r26	d16 0.8000	nd15 1.51633	d15 64.14
r27	d17 1.0106
r28
(Image Plane)
	Aspherical Coefficients
	7th surface
	K 0
	A4 8.0580 105
	A6 7.6927 107
	A8 2.7173 108
	A10 0
	14th surface
	K 0
	A4 1.1033 104
	A6 1.4285 108
	A8 1.8629 108
	A10 0
	21st surface
	K 0
	A4 8.5891 104
	A6 1.0215 105
	A8 3.2143 105
	A10 0
Zooming Data ()
	WE	ST	TE
	f (mm)	5.86879	9.99877	17.39648
	FNO	2.4340	3.2140	4.5000
	2 ( )	61.4	35.8	21.0
	d9	17.88781	8.41716	2.00000
	d13	1.20000	6.81663	3.50000
	d20	3.14136	7.01231	16.74709

[0179]

r1	41.9739	d1	1.2000	nd1	1.77250	vd1	49.60
r2	11.1642	d2	2.9000
r3		d3	6.5000	nd2	1.78590	vd2	44.20
r4	(Mirror)	d4	6.0000	nd3	1.78590	Vd3	44.20
r5		d5	0.3971
r6	28.0000	d6	1.2000	nd4	1.74330	vd4	49.33
r7	11.3578	d7	0.3457
	(Aspheric)
r8	9.4845	d8	1.7925	nd5	1.84666	vd5	23.78
r9	14.2959	d9	(Variable)
r10	(Stop)	d10	1.0000
r11	47.8757	d11	1.9600	nd6	1.72916	vd6	54.68
r12	9.0806	d12	0.7000	nd7	1.72825	vd7	28.46
r13	25.4395	d13	(Variable)
r14	9.1761	d14	1.9500	nd8	1.74330	vd8	49.33
	(Aspheric)
r15	75.3616	d15	0.8461
r16	24.3002	d16	3.8969	nd9	1.74330	vd9	49.33
r17		d17	1.0000	nd10	1.72825	v10	28.46
r18	4.8249	d18	(Variable)
r19	49.5382	d19	2.7500	nd11	1.69350	vd11	53.20
r20	10.0407	d20	0.8269
	(Aspheric)
r21		d21	1.4400	nd12	1.54771	vd12	62.84
r22		d22	0.8000
r23		d23	0.8000	nd13	1.51633	vd13	64.14
r24		d24	1.0447
r25
	(Image
	Plane)
Aspherical Coefficients
7th surface
K	0
A4	2.2504 105
A6	2.6875 106
A8	1.2962 107
A10	2.8718 109
14th surface
K	0
A4	9.8664 105
A6	4.0400 106
A8	4.4986 107
A10	1.3851 108
20th surface
K	0
A4	5.3089 104
A6	1.6198 105
A8	4.4581 107
A10	4.9080 109
Zooming Data ()
	WE	ST	TE
	f (mm)	6.02622	9.31725	14.28897
	FNO	2.7652	3.4888	4.5271
	2 ( )	62.4	42.8	28.7
	d9	14.24100	6.97804	2.00694
	d13	2.10000	6.51339	5.34809
	d18	2.46549	5.31403	11.45279

[0180]

r1	14.2761	d1	5.1000	nd1	1.50913	vd1	56.20
	(Aspheric)
r2	(Mirror)	d2	5.7941	nd2	1.50913	vd2	56.20
r3		d3	2.1000
r4	6.4892	d4	0.8000	nd3	1.64000	vd3	60.07
r5	84.1654	d5	1.1935	nd4	1.84666	vd4	23.78
r6	16.8306	d6	(Variable)
r7	(Stop)	d7	0.4000
r8	34.9225	d8	1.4006	nd5	1.74330	vd5	49.33
	(Aspheric)
r9	15.2934	d9	0.1500
r10	6.1210	d10	3.3481	nd6	1.61800	vd6	63.33
r11	27.4556	d11	0.8000	nd7	1.84666	vd7	23.78
r12	4.9467	d12	(Variable)
r13	13.6380	d13	1.4415	nd8	1.51633	vd8	64.14
r14	143.7586	d14	(Variable)
r15	19.5436	d15	1.3641	nd9	1.58913	vd9	61.25
r16	7.1346	d16	0.8000
	(Aspheric)
r17		d17	1.0500	nd10	1.54771	vd10	62.84
r18		d18	0.8000
r19		d19	0.8000	nd11	1.51633	vd11	64.14
r20		d20	0.9669
r21
	(Image
	Plane)
Aspherical Coefficients
1st surface
K	0
A4	3.2165 104
A6	9.1756 107
A8	4.1788 109
A10	0.0000
8th surface
K	0
A4	1.2083 104
A6	1.1516 107
A8	2.9381 108
A10	0.0000
16th surface
K	0
A4	1.3137 103
A6	2.0878 105
A8	4.9397 107
A10	0.0000
Zooming Data ()
	WE	ST	TE
	f (mm)	5.02898	8.69474	14.52092
	FNO	2.6544	3.5217	4.5079
	2 ( )	64.8	38.2	22.6
	d6	14.61860	7.39251	1.80000
	d12	3.75585	8.20107	4.39975
	d14	3.16733	5.96897	15.38987

[0181] Aberration diagrams for Example 1 and Example 2 upon focused on an object point at infinity are shown in FIG. 13 and FIG. 14, respectively. In these aberration diagrams, spherical aberrations SA, astigmatisms AS, distortions DT and chromatic aberrations of magnification CC are illustrated at the wide-angle end (a), intermediate or standard state (b) and telephoto end (c).

[0182] Enumerated below are the values of L, d/L, D_FT/f_T, M₃/M₂, f₁₁/f₁₂, _Rt, a, and t_LPF concerning conditions (a) to (f) in the aforesaid examples.

Ex.	L	d/L	DFT/fT	M3/M2	f11/f12
1	5.6	0.72088	0.78471	1.19347	0.12343
2	6.0	0.79009	0.76004	0.53348	0.32094
3	5.6	0.71748	0.11496	0.93206	0.36284
4	6.0	0.69413	0.15191	0.92989	0.20195
5	6.64	0.76797	0.25931	3rd-negative	0
6	6.64	0.74877	0.27393	3rd-negative	0
7	6.64	1.19996	0.17676	0.91213	0.37232
8	6.64	1.17430	0.22374	0.93381	0.39484
9	6.64	0.94629	0.21901	0.85382	0.22917
10	6.64	0.85491	0.20119	0.85523	0.05553
11	6.64	0.94867	0.37452	0.73366	0.09671
12	6.0	1.20313	0.30301	0.95350	1.26698

[0183]

	Ex.	Rt	a	tLPF
	1	1.6884	3.0	1.80
	2	1.19598	3.0	1.80
	3	1.49396	3.0	1.80
	4	1.26884	3.0	0.80
	5	1.51672	3.0	1.55
	6	1.38530	3.0	1.44
	7	1.26560	3.0	1.44
	8	1.30121	3.0	1.44
	9	1.05735	3.0	1.44
	10	1.14882	3.0	1.44
	11	0.86588	3.0	1.44
	12	1.36309	2.5	1.20

[0184] How to receive the inventive optical path-bending zoom optical system in place is now explained specifically. FIGS. 15(a) and 15(b) are illustrative of how to receive the optical path-bending zoom optical system of FIG. 9 (Example 9) in place. FIG. 15(b) is a sectional schematic inclusive of an optical path-bending axis, showing Example 9 of the optical path-bending zoom optical system at the wide-angle end. In this state, two lenses forming the second lens group G2 and the optical path-bending prism P forming a part of the 1-1st lens group G1-1 are relocated in a space between the 1-2nd lens group G1-2 and the second lens group G2, and the negative meniscus lens L1 located in front of the optical path-bending prism P in the 1-1st lens group G1-1 is received in the resulting space, so that the thickness of the optical path-bending zoom optical system in its entrance axis direction (in the depth direction of the camera) can be reduced. It is here noted that when there is a space on the image plane I side with respect to the second lens group G2, it is preferable to relocate the optical path-bending prism P and the 1-2nd lens group G1-2 as well as the second lens group G2, etc. on the image plane I side.

[0185] FIG. 16 is a conceptual schematic of one embodiment of how to receive the optical path-bending zoom optical system in place when the reflecting optical element is constructed of a mirror M. The mirror M is tilted at a position indicated by a broken line, and lenses L2 and L3 located on the image plane I side with respect to the mirror M are tilted at positions indicated by broken lines, so that the thickness of the zoom optical system in its optical axis direction (in the depth direction of a camera) can be reduced.

[0186] FIG. 17 is a conceptual schematic of another embodiment of how to receive the optical path-bending zoom optical system in place when the reflecting optical element is formed of a mirror M. The mirror M is tilted at a position indicated by a broken line and a lens group LG located on the object side with respect to the mirror M is received in the resulting space, thereby achieving similar thickness reductions. Instead of tilting the mirror M, it may be relocated along the optical axis after bending, as shown in FIG. 15.

[0187] FIGS. 18(a) and 18(b) are illustrative of one embodiment of the reflecting optical element for bending an optical path, which is constructed of a liquid or transformable prism LP (see FIG. 18(a)). This reflecting optical element may be received in place as by removing the liquid therefrom as shown in FIG. 18(b), thereby achieving thickness reductions. Alternatively, lens groups located on the object side with respect to the prism LP may be received in the resulting space (see FIG. 17), or other lenses may be tilted (see FIG. 16), again achieving thickness reductions.

[0188] In the optical path-bending zoom optical system of the present invention, the reflecting optical element for bending an optical path may also be constructed of a variable-shape mirror. The variable-shape mirror is a reflecting mirror comprising a transformable film with a reflecting mirror coating applied thereon. This reflecting mirror may be relocated by folding or winding.

[0189] When the reflecting optical element for bending an optical path is constructed of a variable-shape mirror, it is acceptable to carry out focusing by the transformation of that mirror, as shown conceptually in FIG. 19. For focusing on a nearby object, only the transformation of a planar form of variable-shape mirror DM into a concave surface is needed upon focused on a point at infinity, as shown by an arrow. That is, for focusing on a nearby object, the surface shape of the variable-shape mirror DM is transformed into an aspheric surface shape within an effective reflecting surface area. Especially when power is imparted to a reflecting surface that is of rotationally symmetric shape, decentration aberrations are produced at that surface due to decentered incidence of light thereon. It is thus desired that the variable-shape mirror DM be defined by a rotationally asymmetric curved surface.

[0190] Off-axis, rotationally asymmetric distortions or the like, too, are produced by decentration. To make correction for decentration aberrations symmetric with respect to plane, it is preferable to transform the surface of the variable-shape mirror DM into a curved surface with respect to plane, where only one symmetric surface is defined by a plane including an optical axis entered in and reflected at the reflecting surface of the variable-shape mirror DM, as shown in FIG. 20.

[0191] Referring again to FIG. 19, the variable-shape mirror DM takes a planar form upon focused on a point at infinity. To make correction for decentration aberrations produced upon focused on a nearby object point, however, it is preferable to transform the reflecting surface of the mirror DM into a rotationally asymmetric surface having only one symmetric plane, as shown in FIG. 20. With this arrangement, it is possible to achieve the size reduction of the whole of an electronic image pickup system and maintain its performance.

[0192] FIG. 21 is illustrative of one embodiment of how to correct camera movements by tilting the reflecting surface of a variable-shape mirror DM in an arrow direction. In the state of FIG. 19, there is no camera movement, and in the state of FIG. 21, the function of correcting camera movements by tilting the reflecting surface of the variable-shape mirror DM is brought into action. When an image pickup device turns down with respect to a phototaking direction as shown in FIG. 21, the inclination of the reflecting surface of the variable-shape mirror DM displaces from a broken-line position to a solid-line position so that the entrance optical axis is kept from inclination. Preferably in this case, the whole surface shape of the variable-shape mirror DM is so transformed that fluctuations of aberrations can be prevented.

[0193] In the present invention, it is acceptable to impart power the reflecting surface of the reflecting optical element for bending an optical path and configure its surface shape with a free-form surface or the like. Alternatively, it is acceptable to construct the reflecting surface of the reflecting optical element with a holographic optical element (HOE).

[0194] When the reflecting optical element is constructed of an optical path-bending prism P as set forth in Examples 1 to 12, it is acceptable to cement the prism P to lenses located before and after the same.

[0195] When an electronic image pickup system such as a digital camera is constructed using the optical path-bending zoom optical system of the present invention, it is acceptable to interpose an optical path splitter element between the optical path-bending zoom optical system and an electronic image pickup device such as a CCD to split an phototaking optical path to a finder optical path, as shown in FIG. 22. FIG. 22 is a front view of a digital camera 40. In this case, an optical path-bending zoom optical system comprises a reflecting optical element Ml for bending an optical path through 90 and a lens group LA located on the image plane side of the element M1, with an image pickup device CCD 49 positioned on the image plane. Between the lens group LA and CCD 49, there is interposed an optical path splitter element M2 half-silvered mirror to split the optical path, so that a part thereof is deflected to a side substantially vertical to a plane including an optical axis before and after reflection at the reflecting optical element M1 (the upper side of FIG. 22). It is understood that the optical path splitter element M2 may be defined by a reflecting surface that is inserted only when a light beam is guided to the finder optical path. An optical path reflected at the optical path splitter element M2 is bent by another reflecting surface M3 through 90 in a plane including an optical axis before and after reflected at the optical path splitter element M2 and further bent by a fourth reflecting surface M4 through 90, running substantially parallel with the optical axis entered in the reflecting optical element M1. Although an eyepiece optical system is not shown in FIG. 22, it is understood that it is located on the exit side of the fourth reflecting surface M4 or before and after a plane including that reflecting surface M4, so that a subject image under observation is viewed by the viewer's eyeball positioned on the exit side of the fourth reflecting surface M4.

[0196] Throughout Examples 1 to 12, the low-pass filter LF is constructed of three filter elements one upon another. However, it is appreciated that many modifications may be made to the aforesaid examples without departing from the scope of the invention. For instance, the low-pass filter may be formed of one single low-pass filter element.

[0197] In each of the aforesaid examples, the final lens group is provided on its image side with a near-infrared cut filter IF or a low-pass filter LF having a near-infrared sharp cut coat surface IC on its entrance surface side. This near-infrared cut filter IF or near-infrared sharp cut coat surface IC is designed to have a transmittance of at least 80% at 600 nm wavelength and a transmittance of up to 10% at 700 nm wavelength. More specifically, the low-pass filter has a multilayer structure made up of such 27 layers as mentioned below; however, the design wavelength is 780 nm.

	Substrate	Material	Physical Thickness (nm)	/4
	1st layer	Al2O3	58.96	0.50
	2nd layer	TiO2	84.19	1.00
	3rd layer	SiO2	134.14	1.00
	4th layer	TiO2	84.19	1.00
	5th layer	SiO2	134.14	1.00
	6th layer	TiO2	84.19	1.00
	7th layer	SiO2	134.14	1.00
	8th layer	TiO2	84.19	1.00
	9th layer	SiO2	134.14	1.00
	10th layer	TiO2	84.19	1.00
	11th layer	SiO2	134.14	1.00
	12th layer	TiO2	84.19	1.00
	13th layer	SiO2	134.14	1.00
	14th layer	TiO2	84.19	1.00
	15th layer	SiO2	178.41	1.33
	16th layer	TiO2	101.03	1.21
	17th layer	SiO2	167.67	1.25
	18th layer	TiO2	96.82	1.15
	19th layer	SiO2	147.55	1.05
	20th layer	TiO2	84.19	1.00
	21st layer	SiO2	160.97	1.20
	22nd layer	TiO2	84.19	1.00
	23rd layer	SiO2	154.26	1.15
	24th layer	TiO2	95.13	1.13
	25th layer	SiO2	160.97	1.20
	26th layer	TiO2	99.34	1.18
	27th layer	SiO2	87.19	0.65

[0198] Air

[0199] The aforesaid near-infrared sharp cut coat has such transmittance characteristics as shown in FIG. 23.

[0200] The low-pass filter LF is provided on its exit surface side with a color filter or coat for reducing the transmission of colors at such a short wavelength band as shown in FIG. 24, thereby enhancing the color reproducibility of electronic images.

[0201] Preferably, such a filter or coat should be such that the ratio of the transmittance of 420 nm wavelength with respect to the transmittance of a wavelength in the range of 400 nm to 700 nm at which the highest transmittance is found is at least 15% and that the ratio of 400 nm wavelength with respect to the highest wavelength transmittance is up to 6%.

[0202] It is thus possible to reduce a discernible difference between the colors perceived by the human eyes and the colors of the image to be picked up and reproduced. In other words, it is possible to prevent degradation in images due to the fact that a color of short wavelength less likely to be perceived through the human sense of sight can be readily seen by the human eyes.

[0203] When the ratio of the 400 nm wavelength transmittance is greater than 6%, the short wavelength region less likely to be perceived by the human eyes would be reproduced with perceivable wavelengths. When the ratio of the 420 nm wavelength transmittance is less than 15%, a wavelength region perceivable by the human eyes is less likely to be reproduced, putting colors in an ill-balanced state.

[0204] Such means for limiting wavelengths can be more effective for image pickup systems using a complementary mosaic filter.

[0205] In each of the aforesaid examples, coating is applied in such a way that, as shown in FIG. 24, the transmittance for 400 nm wavelength is 0%, the transmittance for 420 nm is 90%, and the transmittance for 440 nm peaks or reaches 100%.

[0206] With the synergistic action of the aforesaid near-infrared sharp cut coat and that coating, the transmittance for 400 nm is set at 0%, the transmittance for 420 nm at 80%, the transmittance for 600 nm at 82%, and the transmittance for 700 nm at 2% with the transmittance for 450 nm wavelength peaking at 99%, thereby ensuring more faithful color reproduction.

[0207] The low-pass filter LF is made up of three different filter elements stacked one upon another in the optical axis direction, each filter element having crystallographic axes in directions where, upon projected onto the image plane, the azimuth angle is horizontal (0) and 45 therefrom. Three such filter elements are mutually displaced by a m in the horizontal direction and by SQRT()a in the 45 direction for the purpose of moir control, wherein SQRT means a square root as already mentioned.

[0208] The image pickup plane I of a CCD is provided thereon with a complementary mosaic filter wherein, as shown in FIG. 25, color filter elements of four colors, cyan, magenta, yellow and green are arranged in a mosaic fashion corresponding to image pickup pixels. More specifically, these four different color filter elements, used in almost equal numbers, are arranged in such a mosaic fashion that neighboring pixels do not correspond to the same type of color filter elements, thereby ensuring more faithful color reproduction.

[0209] To be more specific, the complementary mosaic filter is composed of at least four different color filter elements, as shown in FIG. 25, which should preferably have such characteristics as given below.

[0210] Each green color filter element G has a spectral strength peak at a wavelength G_P, each yellow filter element Ye has a spectral strength peak at a wavelength Y_P, each cyan filter element C has a spectral strength peak at a wavelength C_P, and each magenta filter element M has spectral strength peaks at wavelengths M_P1 and M_P2, and these wavelengths satisfy the following conditions.

[0211] To ensure higher color reproducibility, it is preferred that the green, yellow and cyan filter elements have a strength of at least 80% at 530 nm wavelength with respect to their respective spectral strength peaks, and the magenta filter elements have a strength of 10% to 50% at 530 nm wavelength with their spectral strength peak.

[0212] One example of the wavelength characteristics in the aforesaid respective examples is shown in FIG. 26. The green filter element G has a spectral strength peak at 525 nm. The yellow filter element Ye has a spectral strength peak at 555 nm. The cyan filter element C has a spectral strength peak at 510 nm. The magenta filter element M has peaks at 445 nm and 620 nm. At 530 nm, the respective color filter elements have, with respect to their respective spectral strength peaks, strengths of 99% for G, 95% for Ye, 97% for C and 38% for M.

[0213] For such a complementary filter, such signal processing as mentioned below is electrically carried out by means of a controller (not shown) (or a controller used with digital cameras).

[0214] For luminance signals,

[0215] For chromatic signals,

[0216] Through this signal processing, the signals from the complementary filter are converted into R (red), G (green) and B (blue) signals.

[0217] In this regard, it is noted that the aforesaid near-infrared sharp cut coat may be located anywhere on the optical path, and that the number of low-pass filters F may be either two as mentioned above or one.

[0218] One typical detailed aperture stop portion in each example is shown in FIG. 27. At the stop position on the optical axis between the first lens group G1 and the second lens group G2 forming part of the image pickup optical system, there is located a turret 10 capable of making five-stage brightness adjustments at 0, 1, 2, 3 and 4 stages. The turret 10 is provided with a 0 stage adjustment opening 1A having a fixed circular aperture shape of about 4 mm in diameter (which has a 550 nm wavelength transmittance of 100%), a 1 stage correction opening 1B having an aperture area about half that of the opening 1A and a fixed aperture shape and comprising a transparent plane-parallel plate (having a 550 nm wavelength transmittance of 99%) and 2, 3, 4 stage correction openings 1C, 1D and 1E provided with ND filters having a 550 nm wavelength transmittance of 50%, 25% and 13%, respectively.

[0219] The turret 10 is rotated around its rotating shaft 11 to locate any one of the openings at the stop position for light quantity adjustments.

[0220] In the opening, there is also located an ND filter designed to have a 550 nm wavelength transmittance of less than 80% when the effective F-number or F_no is F_no>a/0.4 m. More specifically in Example 1, it is when the effective F-number at the 2 stage is 9.0 upon stop-in (the 0 stage) that the effective F-number at the telephoto end meets the aforesaid formula. The then opening is 1C, so that any image degradation due to diffraction phenomena by the stop is suppressed.

[0221] As shown, a turret 10 of FIG. 28(a) may be used in place of the turret of FIG. 27. This turret 10 is capable of making five-stage brightness adjustments at 0, 1, 2, 3 and 4 stages, and located at an aperture stop position on the optical axis between the first lens group G1 and the second lens group G2 forming part of the image pickup optical system. The turret 10 is provided with a 0-stage adjustment opening 1A having a circular fixed aperture shape of about 4 mm in diameter, a 1 stage correction opening 1B having an aperture area about half that of the opening 1A and a fixed aperture shape, and 2, 3 and 4 stage correction openings 1C, 1D and 1E having a decreasing area in this order. The turret 10 is rotated around its rotating shaft 11 to locate any one of the openings at the stop position for light quantity adjustments.

[0222] A plurality of such openings 1A to 1D are each provided with an optical low-pass filter having different spatial frequency characteristics. As shown in FIG. 28(b), the arrangement is such that the smaller the aperture diameter, the higher the spatial frequency characteristics of the optical filter, thereby reducing any image degradation due to diffraction phenomena by stop-down. The respective curves in FIG. 28(b) show the spatial frequency characteristics of the low-pass filters alone. In this regard, it is noted that the characteristics of the openings inclusive of diffractions by the stops are all equally determined.

[0223] The electronic image pickup system constructed as described above may be applied to phototaking systems where object images formed through image-formation optical systems such as zoom lenses are received at image pickup devices such as CCDs or silver salt films, especially, digital cameras or video cameras as well as PCs and telephone sets which are typical information processors, in particular, easy-to-carry cellular phones. Given below are some such embodiments.

[0224] FIGS. 29 to 31 are conceptual illustrations of a phototaking optical system 41 for digital cameras, in which the image-formation optical system of the invention is incorporated. FIG. 29 is a front perspective view of the outside shape of a digital camera 40, and FIG. 30 is a rear perspective view of the same. FIG. 31 is a sectional view of the construction of the digital camera 40. In this embodiment, the digital camera 40 comprises a phototaking optical system 41 including a phototaking optical path 42, a finder optical system 43 including a finder optical path 44, a shutter 45, a flash 46, a liquid crystal monitor 47 and so on. As the shutter 45 mounted on the upper portion of the camera 40 is pressed down, phototaking takes place through the phototaking optical system 41, for instance, the optical path bending zoom optical system according to Example 2. An object image formed by the phototaking optical system 41 is formed on the image pickup plane of a CCD 49 via a near-infrared cut filter IF and an optical low-pass filter. The object image received at CCD 49 is displayed as an electronic image on the liquid crystal monitor 47 via processing means 51, which monitor is mounted on the back of the camera. This processing means 51 is connected with recording means 52 in which the phototaken electronic image may be recorded. It is here noted that the recording means 52 may be provided separately from the processing means 51 or, alternatively, it may be constructed in such a way that images are electronically recorded and written therein by means of floppy discs, memory cards, MOs or the like. This camera may also be constructed in the form of a silver salt camera using a silver salt camera in place of CCD 49.

[0225] Moreover, a finder objective optical system 53 is located on the finder optical path 44. An object image formed by the finder objective optical path 53 is in turn formed on the field frame 57 of a Porro prism 55 that is an image erecting member. In the rear of the Porro prism 55 there is located an eyepiece optical system 59 for guiding an erected image into the eyeball E of an observer. It is here noted that cover members 50 are provided on the entrance sides of the phototaking optical system 41 and finder objective optical system 53 as well as on the exit side of the eyepiece optical system 59.

[0226] With the thus constructed digital camera 40, it is possible to achieve high performance and cost reductions, because the phototaking optical system 41 is constructed of a fast zoom lens having a high zoom ratio at the wide-angle end with satisfactory aberrations and a back focus large enough to receive a filter, etc. therein.

[0227] In the embodiment of FIG. 31, plane-parallel plates are used as the cover members 50; however, it is acceptable to use powered lenses.

[0228] FIGS. 32 to 34 illustrates a personal computer that is one embodiment of information processors in which the image-formation optical system of the invention is built in the form of an objective optical system. FIG. 32 is a front perspective view of a personal computer or PC 300 in an uncovered state, FIG. 34 is a sectional view of a phototaking optical system 303 in PC 300, and FIG. 34 is a side view of FIG. 32. As shown in FIGS. 32 to 34, PC 300 comprises a keyboard 301 for allowing an operator to enter information therein from outside, information processing and recording means (not illustrated), a monitor 302 for displaying the information to the operator, and a phototaking optical system 303 for photataking an image of the operator per se and nearby images. The monitor 302 used herein may be a transmission type liquid crystal display illuminated from its back side by means of a backlight (not shown), a reflection type liquid crystal display designed to reflect light from its front side for display purposes, a CRT display or the like. As shown, the phototaking optical system 303 is built in the right upper portion of the monitor 302; however, it may be located at any desired position, for instance, around the monitor 302 or the keyboard 301.

[0229] This phototaking optical system 303 comprises an objective lens 112 mounted on a phototaking optical path 304 and formed of the optical path-bending zoom optical system of the invention (roughly shown) and an image pickup chip 162 for receiving images, which are built in PC 300.

[0230] In this embodiment, a low-pass filter LF is additionally applied onto the image pickup chip 162 to form a one-piece unit 160 that can be mounted at the rear end of the lens barrel 113 of the objective lens 112 in one-touch snap operation. Thus, any centering or inter-surface adjustment for the objective lens 112 and image pickup chip 162 can be dispensed with, and so smooth assembly is achieved. Further, the lens barrel 113 is provided at the other end with a cover glass 114 for protection of the objective lens 112. It is here noted that the zoom lens drive mechanism in the lens barrel 113 is not shown.

[0231] An object image received at the image pickup chip 162 is entered into the processing means of PC 300 via a terminal 166 and displayed as an electronic image on the monitor 302. As an example, an image 305 phototaken of the operator is shown in FIG. 32. The image 305 may be displayed on a personal computer on the other end of the line by way of processing means and the Internet or a telephone.

[0232] FIG. 35 is illustrative of a telephone set, especially a convenient-to-carry cellular phone that is one exemplary information processor in which the image-formation optical system of the invention is built as a phototaking optical system. FIGS. 35(a) and 35(b) are a front view and a side view of a cellular phone 400, and FIG. 35(c) is a sectional view of a phototaking optical system 405. As shown in FIGS. 35(a) to 35(c), the cellular phone 400 comprises a microphone 401 through which the voice of an operator is entered as information, a speaker 402 through which the voice of a person on the other end of the like is produced, an input dial 403 through which the information is entered by the operator, a monitor 404 for displaying images phototaken of the operator per se, the person on the other end of the line and so on as well as information such as telephone numbers, a phototaking optical system 405, an antenna 406 for transmission and reception of radio waves for communications, and processing means (not shown) for processing image information, communications information, input signals, etc. Here a liquid crystal display is used for the monitor 404. How the respective devices are arranged is not particularly limited to the arrangement shown in FIG. 41. This phototaking optical system 405 comprises an objective lens 112 mounted on a phototaking optical path 407 and formed of the optical path-bending zoom optical system of the invention (roughly shown) and an image pickup chip 162 for receiving object images, which are built in the cellular phone 400.

[0233] In this embodiment, a low-pass filter LF is additionally applied onto the image pickup chip 162 to form a one-piece unit 160 that can be mounted at the rear end of the lens barrel 113 of the objective lens 112 in one-touch snap operation. Thus, any centering or inter-surface adjustment for the objective lens 112 and image pickup chip 162 can be dispensed with, and so smooth assembly is achieved. Further, the lens barrel 113 is provided at the other end (not shown) with a cover glass 114 for protection of the objective lens 112. It is here noted that the zoom lens drive mechanism in the lens barrel 113, etc. are not shown.

[0234] An object image received at the image pickup chip 162 is entered into processing means (not shown) via a terminal 166, so that the image is displayed as an electronic image on the monitor 404 and/or a monitor on the other end of the line. To transmit the image to the person on the other end, the signal processing means has a signal processing function of converting information on the object image received at the image pickup chip 162 to transmittable signals.

[0235] As can be appreciated from the foregoing explanation, the present invention can provide a zoom lens that is received in a lens mount with smaller thickness and efficiency, has high magnifications and is excellent in image-formation capability even on rear focusing, and enables video cameras or digital cameras to be thoroughly slimmed down.