Taking lens device

Abstract

A taking lens device has a zoom lens system that is comprised of a plurality of lens units and that achieves zooming by varying the unit-to-unit distances and an image sensor that converts an optical image formed by the zoom lens system into an electric signal. The zoom lens system is comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power. The following conditional formula is fulfilled: 1.1<f1/fT<2.5, where f1 represents the focal length of the first lens unit, and fT represents the focal length of the entire optical system at the telephoto end.

Description

[0001] This application is based on Japanese Patent Applications Nos. 2000-111927 and 2000-368339, filed on Apr. 7, 2000 and Dec. 4, 2000, respectively, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an optical or taking lens device. More specifically, the present invention relates to an optical or taking lens device that optically takes in an image of a subject through an optical system and that then outputs the image as an electrical signal by means of an image sensor. For example, a taking lens device that is used as a main component of a digital still camera, a digital video camera, or a camera that is incorporated in, or externally fitted, to a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). The present invention relates particularly to an optical or taking lens device provided with a compact, high-zoom-ratio zoom lens system.

DESCRIPTION OF PRIOR ART

[0003] Conventionally, the majority of high-zoom-ratio zoom lenses for digital cameras are of the type comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a positive optical power (for example, Japanese Patent Application Laid-Open No. H4-296809). This is because a positive-negative-positive-positive configuration excels in compactness.

[0004] On the other hand, as zoom lenses that offer higher zoom ratios are known zoom lenses of the type comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power (for example, Japanese Patent Application Laid-Open No. H5-341189) and zoom lenses of the type comprised of, from the object side, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, a fourth lens unit having a negative optical power, and a fifth lens unit having a positive optical power (for example, Japanese Patent Application Laid-Open No. H10-111457).

[0005] However, in the zoom lens of a positive-negative-positive-negative configuration proposed in Japanese Patent Application Laid-Open No. H5-341189, mentioned above, the first lens unit is kept stationary during zooming, and therefore this zoom lens is unfit for further improvement for higher performance necessitated by the trend toward higher zoom ratios and smaller image-sensor pixel pitches. On the other hand, in the zoom lens of a positive-negative-positive-negative-positive configuration proposed in Japanese Patent Application Laid-Open No. H10-111457, mentioned above, the first lens unit is moved during zooming, but the individual lens units, in particular the first and second lens units, are given strong optical powers and thus cause large aberrations. This makes it difficult to achieve higher performance necessitated by the trend toward higher zoom ratios and smaller image-sensor pixel pitches. In addition, a configuration including a positive-negative-positive-negative sequence, in which the fourth lens unit is negative, is somewhat inferior in compactness to a positive-negative-positive-positive configuration.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a zoom lens configuration that is superior in compactness to a positive-negative-positive-positive configuration but that still offers satisfactory performance. In particular, an object of this invention is to provide an optical or taking lens device provided with a high-zoom-ratio zoom lens system that offers a zoom ratio of about 7× to 10× and an f-number of about 2.5 to 4, that offers such high performance that it can be used as an optical system for use with a leading-edge image sensor with a very small pixel pitch, and that excels in compactness.

[0007] To achieve the above object, according to one aspect of the present invention, an optical or taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units and that achieves zooming by varying the unit-to-unit distances; and an image sensor that converts an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises at least, from the object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power. Here, the following conditional formula is fulfilled:

1.1<f1/fT<2.5

[0008] where

[0009] f1 represents the focal length of the first lens unit; and

[0010] fT represents the focal length of the entire optical system at the telephoto end.

[0011] According to another aspect of the present invention, an optical, or taking lens device is provided with: a zoom lens system that is comprised of a plurality of lens units which achieves zooming by varying the unit-to-unit distances; and an image sensor for converting an optical image formed by the zoom lens system into an electrical signal. The zoom lens system comprises at least, from an object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power. The first lens unit is moved as zooming is performed. Here, the following conditional formula is fulfilled:

0.3<D34W/D34T<2.5

[0012] where

[0013] D34W represents the aerial distance between the third lens unit and the fourth lens unit at the wide-angle end; and

[0014] D34T represents the aerial distance between the third lens unit and the fourth lens unit at the telephoto end.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] This and other objects and features of the present invention will become clear from the following description, taken in conjunction with the preferred embodiments with reference to the accompanying drawings in which:

[0016] FIG. 1 is a lens arrangement diagram of a first embodiment (Example 1) of the invention;

[0017] FIG. 2 is a lens arrangement diagram of a second embodiment (Example 2) of the invention;

[0018] FIG. 3 is a lens arrangement diagram of a third embodiment (Example 3) of the invention;

[0019] FIG. 4 is a lens arrangement diagram of a fourth embodiment (Example 4) of the invention;

[0020] FIG. 5 is a lens arrangement diagram of a fifth embodiment (Example 5) of the invention;

[0021] FIG. 6 is a lens arrangement diagram of a sixth embodiment (Example 6) of the invention;

[0022] FIG. 7 is a lens arrangement diagram of a seventh embodiment (Example 7) of the invention;

[0023] FIG. 8 is a lens arrangement diagram of a eighth embodiment (Example 8) of the invention;

[0024] FIG. 9 is a lens arrangement diagram of a ninth embodiment (Example 9) of the invention;

[0025] FIGS. 10A to 10I are aberration diagrams of Example 1, as observed when focused at infinity;

[0026] FIGS. 11A to 11I are aberration diagrams of Example 2, as observed when focused at infinity;

[0027] FIGS. 12A to 12I are aberration diagrams of Example 3, as observed when focused at infinity;

[0028] FIGS. 13A to 13I are aberration diagrams of Example 4, as observed when focused at infinity;

[0029] FIGS. 14A to 14I are aberration diagrams of Example 5, as observed when focused at infinity;

[0030] FIGS. 15A to 15I are aberration diagrams of Example 6, as observed when focused at infinity;

[0031] FIGS. 16A to 16I are aberration diagrams of Example 7, as observed when focused at infinity;

[0032] FIGS. 17A to 17I are aberration diagrams of Example 8, as observed when focused at infinity;

[0033] FIGS. 18A to 18I are aberration diagrams of Example 9, as observed when focused at infinity;

[0034] FIGS. 19A to 19F are aberration diagrams of Example 1, as observed when focused at a close-up distance (D=0.5 m);

[0035] FIGS. 20A to 20F are aberration diagrams of Example 2, as observed when focused at a close-up distance (D=0.5 m);

[0036] FIGS. 21A to 21F are aberration diagrams of Example 3, as observed when focused at a close-up distance (D=0.5 m);

[0037] FIGS. 22A to 22F are aberration diagrams of Example 4, as observed when focused at a close-up distance (D=0.5 m);

[0038] FIGS. 23A to 23F are aberration diagrams of Example 5, as observed when focused at a close-up distance (D=0.5 m);

[0039] FIGS. 24A to 24F are aberration diagrams of Example 8, as observed when focused at a close-up distance (D=0.5 m);

[0040] FIGS. 25A to 25F are aberration diagrams of Example 9, as observed when focused at a close-up distance (D=0.5 m);

[0041] FIG. 26 is a diagram schematically illustrating the outline of the optical construction of a taking lens device embodying the invention; and

[0042] FIG. 27 is a diagram schematically illustrating the outline of a construction of an embodiment of the invention that could be used in a digital camera.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Hereinafter, optical or taking lens devices embodying the present invention will be described with reference to the drawings and optical or taking lens devices will be referred to as taking lens devices. A taking lens device optically takes in an image of a subject and then outputs the image as an electrical signal. A taking lens device is used as a main component of a camera used to shoot a still or moving pictures of a subject, for example a digital still camera, a digital video camera, or a camera that is incorporated in or externally fitted to a device such as a digital video unit, a personal computer, a mobile computer, a portable telephone, or a personal digital assistant (PDA). A digital camera also includes a memory to store the image data from the image sensor. The memory may be removable, for example, a disk, or the memory may be permanently installed in the camera. FIG. 26 shows a taking lens device comprised of, from the object (subject) side, a taking lens system (TL) that forms an optical image of an object, a plane-parallel plate (PL) that functions as an optical low-pass filter or the like, and an image sensor (SR) that converts the optical image formed by the taking lens system (TL) into an electrical signal. FIG. 27 shows a zoom lens system ZL, an optical low-pass filter PL, an image sensor SR, processing circuits PC that would include any electronics needed to process the image, and a memory EM that could be used in a digital camera.

[0044] In all of the embodiments described hereinafter, the taking lens system TL is built as a zoom lens system comprised of a plurality of lens units wherein zooming is achieved by moving two or more lens units along the optical axis AX in such a way that their unit-to-unit distances vary. The image sensor SR is realized, for example, with a solid-state image sensor such as a CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) sensor having a plurality of pixels, and, by this image sensor SR, the optical image formed by the zoom lens system is converted into an electrical signal. The optical image to be formed by the zoom lens system has its spatial frequency characteristics adjusted by being passed through the low-pass filter PL that has predetermined cut-off frequency characteristics that are determined by the pixel pitch of the image sensor SR. This helps minimize so-called aliasing noise that appears when the optical image is converted into an electrical signal. The signal produced by the image sensor SR is subjected, as required, to predetermined digital image processing, image compression, and other processing, and is then, as a digital image signal, recorded in a memory (such as a semiconductor memory or an optical disk) or, if required, transmitted to another device by way of a cable or after being converted into an infrared signal.

[0045] FIGS. 1 to 9 are lens arrangement diagrams of the zoom lens system used in a first to a ninth embodiment of the present invention, each showing the lens arrangement at the wide-angle end W in an optical sectional view. In each lens arrangement diagram, an arrow mj (j=1, 2, . . . ) schematically indicates the movement of the j-th lens unit Grj during zooming from the wide-angle end W to the telephoto end T (a broken-line arrow mj, however, indicates that the corresponding lens unit is kept stationary during zooming), and an arrow mF indicates the direction in which the focusing unit is moved during focusing from infinity to a close-up distance. Moreover, in each lens arrangement diagram, ri (i=1, 2, 3, . . . ) indicates the i-th surface from the object (subject) side, and a surface ri marked with an asterisk (*) is an aspherical surface. Di (i=1, 2, 3, . . . ) indicates the i-th axial distance from the object side, though only those which vary with zooming, called variable distances, are shown here.

[0046] In all of the embodiments, the zoom lens system includes, from the object side, a first lens unit Gr1 having a positive optical power, a second lens unit Gr2 having a negative optical power, a third lens unit Gr3 having a positive optical power, and a fourth lens unit Gr4 having a negative optical power. In addition, designed for a camera (for example, a digital camera) provided with a solid-state image sensor (for example, a CCD), the zoom lens system also has a flat glass plate PL, which is a glass plane-parallel plate that functions as an optical low-pass filter or the like, disposed on the image-plane side thereof. In all of the embodiments, the flat glass plate PL is kept stationary during zooming, and the third lens unit Gr3 includes an aperture stop ST at the object-side end thereof.

[0047] In the first embodiment, the zoom lens system is a four-unit zoom lens of a positive-negative-positive-negative configuration, and is comprised of, from the object side, a first lens unit Gr1 having a positive optical power, a second lens unit Gr2 having a negative optical power, a third lens unit Gr3 having a positive optical power, and a fourth lens unit Gr4 having a negative optical power. In the second to the fourth, the sixth, the eighth, and the ninth embodiments, the zoom lens system is a five-unit zoom lens of a positive-negative-positive-negative-positive configuration, and is comprised of, from the object side, a first lens unit Gr1 having a positive optical power, a second lens unit Gr2 having a negative optical power, a third lens unit Gr3 having a positive optical power, a fourth lens unit Gr4 having a negative optical power, and a fifth lens unit Gr5 having a positive optical power.

[0048] In the fifth embodiment, the zoom lens system is a six-unit zoom lens of a positive-negative-positive-negative-positive-negative configuration, and is comprised of, from the object side, a first lens unit Gr1 having a positive optical power, a second lens unit Gr2 having a negative optical power, a third lens unit Gr3 having a positive optical power, a fourth lens unit Gr4 having a negative optical power, a fifth lens unit Gr5 having a positive optical power, and a sixth lens unit Gr6 having a negative optical power. In the seventh embodiment, the zoom lens system is a six-unit zoom lens of a positive-negative-positive-negative-positive-positive configuration, and is comprised of, from the object side, a first lens unit Gr1 having a positive optical power, a second lens unit Gr2 having a negative optical power, a third lens unit Gr3 having a positive optical power, a fourth lens unit Gr4 having a negative optical power, a fifth lens unit Gr5 having a positive optical power, and a sixth lens unit Gr6 having a positive optical power.

[0049] n all of the embodiments, the zoom lens system has a configuration starting with a positive-negative-positive-negative sequence. As compared with a configuration starting with a positive-negative-positive-positive sequence, in which both the third lens unit and the fourth lens unit Gr3, Gr4 have positive powers, a configuration starting with a positive-negative-positive-negative sequence, in which the fourth lens unit Gr4 is negative, the opposite signs of the optical powers of the third lens unit and the fourth lens unit Gr3, Gr4 permit a high zoom ratio to be achieved with those lens units Gr3, Gr4 alone, and thus makes it easier to secure a high zoom ratio through the entire zoom lens system. It is to be noted that configurations starting with a positive-negative-positive-negative sequence include the following variations: a four-unit type having a positive-negative-positive-negative configuration, five-unit types respectively having a positive-negative-positive-negative-positive and a positive-negative-positive-negative-negative configuration, six-unit types having a positive-negative-positive-negative-positive-positive, a positive-negative-positive-negative-positive-negative, a positive-negative-positive-negative-negative-positive, and a positive-negative-positive-negative-negative-negative configuration, and so forth.

[0050] In a zoom lens system, like those used in the embodiments, of the type that includes, from the object side, positive-negative-positive-negative zoom units, it is preferable that conditional formula (1) below be fulfilled. This makes it possible to realize a compact, high-zoom-ratio zoom lens system. In addition, the thus realized zoom lens system offers a zoom ratio of about 7× to 10×, an f-number of about 2.5 to 4, and high performance that makes the zoom lens system usable as an optical system for use with a leading-edge image sensor SR with a very small pixel pitch.

1.1<f1/fT<2.5  (1)

[0051] where

[0052] f1 represents the focal length of the first lens unit Gr1; and

[0053] fT represents the focal length of the entire optical system at the telephoto end T.

[0054] If the lower limit of conditional formula (1) were to be transgressed, the optical power of the first lens unit Gr1 would be too strong, and thus it would be difficult to eliminate spherical aberration, in particular, at the wide-angle end W. By contrast, if the upper limit of conditional formula (1) were to be transgressed, the optical power of the first lens unit Gr1 would be too weak, and thus it would be difficult to achieve satisfactory compactness, in particular, at the telephoto end T.

[0055] In a zoom lens system, like those used in the embodiments, of the type that includes, from the object side, positive-negative-positive-negative zoom units, it is preferable that focusing be achieved by moving the fourth lens unit Gr4 along the optical axis AX and that conditional formula (2) below be additionally fulfilled. This makes it possible to realize a zoom lens system offering higher performance. It is further preferable that conditional formula (2) be fulfilled together with conditional formula (1) noted previously.

0.3<|f4/fT|<2  (2)

[0056] where

[0057] f4 represents the focal length of the fourth lens unit Gr4; and

[0058] fT represents the focal length of the entire optical system at the telephoto end T.

[0059] As conditional formula (2) suggests, the fourth lens unit Gr4 has a relatively weak optical power, and accordingly the fourth lens unit Gr4 has the fewest lens elements. Thus, focusing is best achieved by moving (as indicated by the arrow mF) the fourth lens unit Gr4, which is light, along the optical axis AX. However, in cases where it is possible to adopt a system that permits the image sensor SR to be moved for focusing, focusing may be achieved instead by moving the image sensor SR.

[0060] If the lower limit of conditional formula (2) were to be transgressed, the optical power of the fourth lens unit Gr4 would be so strong that it would be difficult to eliminate performance degradation at close-up distances, in particular, at the telephoto end T. By contrast, if the upper limit of conditional formula (2) were to be transgressed, the optical power of the fourth lens unit Gr4 would be so weak that the fourth lens unit Gr4 would need to be moved through an unduly long distance for focusing. This would spoil the compactness of the lens barrel structure as a whole.

[0061] It is preferable that, as in all the embodiments, as zooming is performed from the wide-angle end W to the telephoto end T, the first lens unit Gr1 be moved and the distance between the third and fourth lens units Gr3, Gr4 increase from the wide-angle end W to the middle-focal-length position and decrease from the middle-focal-length position to the telephoto end T. This makes it possible to realize a high-zoom-ratio zoom lens system. In this distinctive zoom arrangement, it is further preferable that conditional formulae (1) and (2) be fulfilled.

[0062] Conventionally, the majority of optical systems used in video cameras or digital cameras are so constructed that their first lens unit Gr1 is kept stationary during zooming, because this construction offers a proper balance between the compactness of the product as a whole and the complexity of lens barrel design. However, considering the current trend toward further compactness and higher zoom ratios, it is preferable to make the first lens unit Gr1 movable. By moving the first lens unit Gr1 toward the object side during zooming from the wide-angle end W to the telephoto end T, it is possible to lower the heights at which rays enter the second lens unit Gr2 at the telephoto end T. This makes aberration correction easier. Moreover, by adopting an arrangement in which, during zooming from the wide-angle end W to the telephoto end T, the distance between the third lens unit and the fourth lens unit Gr3, Gr4 increases from the wide-angle end W to the middle-focal-length position and decreases from the middle-focal-length position to the telephoto end T, it is possible to properly correct the curvature of filed that occurs in the middle-focal-length region. This makes it possible to realize a high-zoom-ratio zoom lens system.

[0063] It is preferable to dispose, as in all of the embodiments, an aspherical surface in the second lens unit Gr2. Disposing an aspherical surface in the second lens unit Gr2 makes it possible to realize a zoom lens system of which the zoom range starts at a wider angle. An attempt to increase the shooting view angle by reducing the focal length at the wide-angle end W results in making correction of distortion difficult, in particular, at the wide-angle end W. To avoid this inconvenience, it is preferable to dispose an aspherical surface in the second lens unit Gr2 through which off-axial rays pass at relatively great heights on the wide-angle side. This makes proper correction of distortion possible. Thus, to obtain high optical performance without sacrificing compactness, it is further preferable that conditional formulae (1) and (2) be fulfilled and in addition that an aspherical surface be disposed in the second lens unit Gr2.

[0064] In a zoom lens system, like those used in the embodiments, of the type that includes, from the object side, positive-negative-positive-negative zoom units and in which the first lens unit Gr1 is moved during zooming, it is preferable that conditional formula (3) below be fulfilled. This makes it possible to realize a compact, high-zoom-ratio zoom lens system. In addition, the thus realized zoom lens system offers a zoom ratio of about 7× to 10×, an f-number of about 2.5 to 4, and high performance that makes the zoom lens system usable as an optical system for use with a leading-edge image sensor SR with a very small pixel pitch.

0.3<D34W/D34T<2.5  (3)

[0065] where

[0066] D34W represents the aerial distance between the third lens unit and the fourth lens unit Gr3, Gr4 at the wide-angle end W; and

[0067] D34T represents an aerial distance between the third lens unit and the fourth lens unit Gr3, Gr4 at the telephoto end T.

[0068] If the lower limit of conditional formula (3) were to be transgressed, the aerial distance between the third lens unit and the fourth lens unit Gr3, Gr4 at the telephoto end T would be so long that it would be difficult to achieve satisfactory compactness at the telephoto end T. By contrast, if the upper limit of conditional formula (3) were to be transgressed, the aerial distance between the third lens unit and the fourth lens unit Gr3, Gr4 at the wide-angle end W is so long that it would be difficult to achieve satisfactory compactness at the wide-angle end W.

[0069] In a zoom lens system, like those used in the embodiments, of the type that includes, from the object side, positive-negative-positive-negative zoom units, it is preferable that, during zooming from the wide-angle end W to the telephoto end T, the first lens unit Gr1 be moved as described previously and, in addition, that the fourth lens unit Gr4 be moved toward the object side. This makes it possible to obtain a higher zoom ratio in the fourth lens unit Gr4, and thereby obtain an accordingly higher zoom ratio through the entire zoom lens system. To strike a proper balance between a high zoom ratio and compactness, it is further preferable that conditional formula (3) be fulfilled simultaneously.

[0070] In a zoom lens system, like those used in the embodiments, of the type that includes, from the object side, positive-negative-positive-negative zoom units, it is preferable that, as zooming is performed from the wide-angle end W to the telephoto end T, the distance between the third lens unit and the fourth lens unit Gr3, Gr4 increase from the wide-angle end W to the middle-focal-length position and decrease from the middle-focal-length position to the telephoto end T as described previously. To achieve satisfactory compactness, it is further preferable that conditional formula (3) be fulfilled simultaneously. By moving the third lens unit and the fourth lens unit Gr3, Gr4 in this way for zooming, it is possible to properly correct the curvature of field that occurs toward the under side, in particular, in the middle-focal-length region, and thereby realize a zoom lens system that keeps high performance.

[0071] In a zoom lens system, like those used in the embodiments, of the type that includes, from the object side, positive-negative-positive-negative zoom units, it is preferable that focusing be achieved by moving the fourth lens unit Gr4, as described previously, and that conditional formula (4) below be additionally fulfilled. This makes it possible to realize a zoom lens system offering higher performance. It is further preferable that conditional formula (4) be fulfilled together with conditional formula (3) noted previously.

0.5<&bgr;W4<2  (4)

[0072] where

[0073] &bgr;W4 represents the lateral magnification of the fourth lens unit Gr4 at the wide-angle end W.

[0074] As described previously, the fourth lens unit Gr4 has a relatively weak optical power, and accordingly the fourth lens unit Gr4 has the fewest lens elements. Thus, the fourth lens unit Gr4, which is light, is best suited for focusing. However, in cases where it is possible to adopt a system that permits focusing using the image sensor SR, focusing may be achieved instead by moving the image sensor SR.

[0075] If the lower limit of conditional formula (4) were to be transgressed, the zoom ratio distributed to the fourth lens unit Gr4 would be so low at the wide-angle end W that an unduly high zoom ratio would need to be distributed to the third lens unit Gr3. As a result, it would be difficult to eliminate the aberrations that would occur in the third lens unit Gr3. By contrast, if the upper limit of conditional formula (4) were to be transgressed, the zoom ratio distributed to the fourth lens unit Gr4 would be so high that it would be difficult to eliminate the aberrations that would occur in the fourth lens unit Gr4. As a result, it would be impossible to realize a compact zoom lens system.

[0076] As described earlier, disposing an aspherical surface in the second lens unit Gr2 makes it possible to realize a zoom lens system of which the zoom range starts at a wider angle. An attempt to increase the shooting view angle by reducing the focal length at the wide-angle end W results in making correction of distortion difficult, in particular, at the wide-angle end W. To avoid this inconvenience, it is preferable to dispose an aspherical surface in the second lens unit Gr2 through which off-axial rays pass at relatively great heights on the wide-angle side. This makes proper correction of distortion possible. Thus, to obtain high optical performance without sacrificing compactness, it is further preferable that conditional formulae (3) and (4) be fulfilled and in addition that an aspherical surface be disposed in the second lens unit Gr2.

[0077] In all of the first to the ninth embodiments, all of the lens units are comprised solely of refractive lenses that deflect light incident thereon by refraction (i.e. lenses of the type that deflects light at the interface between two media having different refractive indices). However, any of these lens units may include, for example, a diffractive lens that deflects light incident thereon by diffraction, a refractive-diffractive hybrid lens that deflects light incident thereon by the combined effects of refraction and diffraction, a gradient-index lens that deflects light incident thereon with varying refractive indices distributed in a medium, or a lens of any other type.

[0078] In any of the embodiments, a surface having no optical power (for example, a reflective, refractive, or diffractive surface) may be disposed in the optical path so that the optical path is bent before, after, or in the middle of the zoom lens system. Where to bend the optical path may be determined to suit particular needs. By bending the optical path appropriately, it is possible to make a camera slimmer. It is even possible to build an arrangement in which zooming or the collapsing movement of a lens barrel does not cause any change in the thickness of a camera. For example, by keeping the first lens unit Gr1 stationary during zooming, and disposing a mirror behind the first lens unit Gr1 so that the optical path is bent by 90° by the reflecting surface of the mirror, it is possible to keep the front-to-rear length of the zoom lens system constant and thereby make the camera slimmer.

[0079] In all of the embodiments, an optical low-pass filter having the shape of a plane-parallel plate PL is disposed between the last surface of the zoom lens system and the image sensor SR. However, as this low-pass filter, it is also possible to use a birefringence-type low-pass filter made of quartz or the like having its crystal axis aligned with a predetermined direction, a phase-type low-pass filter that achieves the required optical cut-off frequency characteristics by exploiting diffraction, or a low-pass filter of any other type.

Practical Examples

[0080] Hereinafter, practical examples of the construction of the zoom lens system used in taking lens devices embodying the present invention will be presented in more detail with reference to their construction data, aberration diagrams, and other data. Examples 1 to 9 presented below correspond to the first embodiment to the ninth embodiment, respectively, as described hereinbefore, and the lens arrangement diagrams (FIGS. 1 to 9) showing the lens arrangement of the first to ninth embodiments apply also to Examples 1 to 9, respectively.

[0081] Tables 1 to 9 list the construction data of Examples 1 to 9, respectively. In the construction data of each example, ri (i=1, 2, 3, . . . ) represents the radius of curvature (mm) of the i-th surface from the object side, di (i=1, 2, 3, . . . ) represents the i-th axial distance (mm) from the object side, and Ni (i=1, 2, 3, . . . ) and &ngr;i (i=1, 2, 3, . . . ) represent the refractive index Nd for the d-line and the Abbe number (&ngr;d) of the i-th optical element from the object side, respectively. Moreover, in the construction data, for each of those axial distances that vary with zooming (i.e., variable aerial distances), three values are given that are, from left, the axial distance at the wide-angle end W (the shortest-focal-length end), the axial distance in the middle position M (the middle-focal-length position), and the axial distance at the telephoto end T (the longest-focal-length end). Also listed are the focal length F (in mm) and the f-number FNO of the entire optical system in those three focal-length positions W, M, and T. Table 10 lists the movement distance (focusing data) of the fourth lens unit Gr4 when focusing at a close-up distance (shooting distance: D=0.5 m), and Table 11 lists the values of the conditional formulae, both as actually observed in Examples 1 to 9.

[0082] A surface whose radius of curvature ri is marked with an asterisk (*) is an aspherical surface, of which the surface shape is defined by formula (AS) below. The aspherical surface data of Examples 1 to 9 is also listed in their respective construction data.

X(H)=(C0·H2)/(1+{square root}{square root over (1−&egr;·C02·H2)})

+(A4·H4+A6·H6+A8·H8+A10·H10)  (AS)

[0083] where

[0084] X(H) represents the displacement along the optical axis at the height H (relative to the vertex);

[0085] H represents the height in a direction perpendicular to the optical axis;

[0086] C0 represents the paraxial curvature (the reciprocal of the radius of curvature);

[0087] &egr; represents the quadric surface parameter; and

[0088] Ai represents the aspherical surface coefficient of i-th order.

[0089] FIGS. 10A-10I, 11A-11I, 12A-12I, 13A-13I, 14A-14I, 15A-15I, 16A-16I, 17A-17I, and 18A-18I are diagrams showing the aberration observed in Examples 1 to 9, respectively, when focused at infinity. FIGS. 19A-19F, 20A-20F, 21A-21F, 22A-22F, 23A-23F, 24A-24F, and 25A-25F are diagrams showing the aberration observed in Examples 1 to 5, 8, and 9, respectively, when focused at a close-up distance (shooting distance: D=0.5 m). Of these diagrams, FIGS. 10A-10C, 11A-11C, 12A-12C, 13A-13C, 14A-14C, 15A-15C, 16A-16C, 17A-17C, 18A-18C, 19A-19C, 20A-20C, 21A-21C, 22A-22C, 23A-23C, 24A-24C, and 25A-25C show the aberration observed at the wide-angle end W, FIGS. 10D-10F, 11D-11F, 12D-12F, 13D-13F, 14D-14F, 15D-15F, 16D-16F, 17D-17F, and 18D-18F show the aberration observed in the middle position M, and 10G-10I, 11G-11I, 12G-12I, 13G-13I, 14G-14I, 15G-15I, 16G-16I, 17G-17I, 18G-18I, 19D-19F, 20D-20F, 21D-21F, 22D-22F, 23D-23F, 24D-24F, and 25D-25F show the aberration observed at the telephoto end T. Of these diagrams, FIGS. 10A, 10D, 10G, 11A, 11D, 11G, 12A, 12D, 12G, 13A, 13D, 13G, 14A, 14D, 14G, 15A, 15D, 15G, 16A, 16D, 16G, 17A, 17D, 17G, 18A, 18D, 18G, 19A, 19D, 20A, 20D, 21A, 21D, 22A, 22D, 23A, 23D, 24A, 24D, 25A, and 25D show spherical aberration, FIGS. 10B, 10E, 10H, 11B, 11E, 11H, 12B, 12E, 12H, 13B, 13E, 13H, 14B, 14E, 14H, 15B, 15E, 15H, 16B, 16E, 16H, 17B, 17E, 17H, 18B, 18E, 18H, 19B, 19E, 20B, 20E, 21B, 21E, 22B, 22E, 23B, 23E, 24B, 24E, 25B, and 25E show astigmatism, and FIGS. 10C, 10F, 10I, 11C, 11F, 11I, 12C, 12F, 12I, 13C, 13F, 13I, 14C, 14F, 14I, 15C, 15F, 15I, 16C, 16F, 16I, 17C, 17F, 17I, 18C, 18F, 18I, 19C, 19F, 20C, 20F, 21C, 21F, 22C, 22F, 23C, 23F, 24C, 24F, 25C, and 25F show distortion. In these diagrams, Y′ represents the maximum image height (mm). In the diagrams showing spherical aberration, a solid line d and a dash-and-dot line g show the spherical aberration for the d-line and for the g-line, respectively, and a broken line SC shows the sine condition. In the diagrams showing astigmatism, a broken line DM and a solid line DS represent the astigmatism for the d-line on the meridional plane and on the sagittal plane, respectively. In the diagrams showing distortion, a solid line represents the distortion (%) for the d-line. 1 TABLE 1 Construction Data of Example 1 f = 7.5˜25.5˜50.6, FNO = 2.55˜2.96˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 63.832 d1 = 1.200 N1 = 1.74000 &ngr;1 = 28.26 r2 = 46.105 d2 = 4.909 N2 = 1.49310 &ngr;2 = 83.58 r3 = 557.712 d3 = 0.100 r4 = 41.139 d4 = 3.518 N3 = 1.49310 &ngr;3 = 83.58 r5 = 95.433 d5 = 1.000˜28.553˜ 40.964 r6 = 28.766 d6 = 0.800 N4 = 1.80420 &ngr;4 = 46.50 r7 = 8.145 d7 = 6.254 r8 = −24.683 d8 = 0.800 N5 = 1.80741 &ngr;5 = 31.59 r9 = 408.759 d9 = 2.972 N6 = 1.84666 &ngr;6 = 23.82 r10 = −15.616 d10 = 0.727 r11 = −12.222 d11 = 0.800 N7 = 1.52510 &ngr;7 = 56.38 r12* = −72.536 d12 = 24.622˜4.490˜ 1.000 r13 = ∞(ST) d13 = 0.800 r14 = 11.863 d14 2.033 N8 = 1.78831 &ngr;8 = 47.32 r15 = 212.313 d15 = 5.251 r16 = −66.079 d16 = 1.795 N9 = 1.48749 &ngr;9 = 70.44 r17 = −10.997 d17 = 0.800 N10 = 1.84666 &ngr;10 = 23.82 r18* = 29.156 d18 = 0.100 r19 = 12.934 d19 = 3.092 N11 = 1.48749 &ngr;11 = 70.44 r20* = −19.433 d20 = 0.100 r21 = −788.619 d21 = 4.662 N12 = 1.79850 &ngr;12 = 22.60 r22 = −27.115 d22 = 1.000˜7.000˜ 1.000 r23 = 23.066 d23 = 0.800 N13 = 1.85000 &ngr;13 = 40.04 r24 = 11.361 d24 = 3.500 r25 = 11.740 d25 = 1.826 N14 = 1.79850 &ngr;14 = 22.60 r26 = 14.538 d26 = 2.381˜2.000˜ 13.578 r27 = ∞ d27 = 3.000 N15 = 1.51680 &ngr;15 = 64.20 r28 = ∞ Aspherical Surface Data of Surface r12 &egr; = 1.0000, A4 = −0.90791 × 10−4, A6 = −0.27514 × 10−6, A8 = −0.37035 × 10−8 Aspherical Surface Data of Surface r18 &egr; = 1.0000, A4 = 0.28853 × 10−3, A6 = 0.12716 × 10−5, A8 = 0.10778 × 10−7 Aspherical Surface Data of Surface r20 &egr; = 1.0000

[0090] 2 TABLE 2 Construction Data of Example 2 f = 7.5˜25.5˜50.6, FNO = 2.48˜3.07˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 62.012 d1 = 1.200 N1 = 1.79850 &ngr;1 = 22.60 r2 = 50.059 d2 = 3.893 N2 = 1.49310 &ngr;2 = 83.58 r3 = 264.139 d3 = 0.100 r4 = 57.561 d4 = 2.818 N3 = 1.49310 &ngr;3 = 83.58 r5 = 155.066 d5 = 1.000˜30.739˜ 48.448 r6 = 29.965 d6 = 0.800 N4 = 1.75450 &ngr;4 = 51.57 r7 = 9.032 d7 = 7.570 r8 = −52.559 d8 = 0.800 N5 = 1.75450 &ngr;5 = 51.57 r9 = 21.530 d9 = 4.134 N6 = 1.79850 &ngr;6 = 22.60 r10 = −18.800 d10 = 0.486 r11 = −15.910 d11 = 0.800 N7 = 1.84666 &ngr;7 = 23.82 r12* = −107.564 d12 = 25.513˜ 4.405˜1.000 r13 = ∞(ST) d13 = 0.800 r14 = 13.086 d14 = 1.832 N8 = 1.80750 &ngr;v = 35.43 r15 = 84.611 d15 = 3.644 r16 = 15.627 d16 = 2.756 N9 = 1.75450 &ngr;9 = 51.57 r17 = −12.357 d17 = 0.800 N10 = 1.84666 &ngr;10 = 23.82 r18 = 9.111 d18 = 0.100 r19 = 7.143 d19 = 1.343 N11 = 1.52510 &ngr;11 = 56.38 r20* = 13.828 d20 = 2.118 r21 = 31.671 d21 = 1.530 N12 = 1.79850 &ngr;12 = 22.60 r22 = −35.431 d22 = 1.000˜5.669˜ 4.095 r23 = 26.961 d23 = 0.800 N13 = 1.85000 &ngr;13 = 40.04 r24 = 9.331 d24 = 2.307 r25 = 11.028 d25 = 1.289 N14 = 1.79850 &ngr;14 = 22.60 r26 = 14.503 d26 = 2.123˜2.989˜ 8.644 r27 = −130.604 d27 = 1.347 N15 = 1.79850 &ngr;15 = 22.60 r28 = −33.480 d28 = 0.858 r29 = ∞ d29 = 3.000 N16 = 1.51680 &ngr;16 = 64.20 r30 = ∞ Aspherical Surface Data of Surface r12 &egr; = 1.0000, A4 = −0.44023 × 10−4, A6 = −0.52908 × 10−7, A8 = −0.21921 × 10−8 Aspherical Surface Data of Surface r20 &egr; = 1.0000, A4 = 0.52117 × 10−3, A6 = 0.41505 × 10−5, A8 = 0.98968 × 10−7

[0091] 3 TABLE 3 Construction Data of Example 3 f = 7.4˜23.0˜49.5, FNO = 2.22˜2.64˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 63.356 d1 = 1.200 N1 = 1.79850 &ngr;1 = 22.60 r2 = 49.435 d2 = 4.655 N2 = 1.49310 &ngr;2 = 83.58 r3 = 579.022 d3 = 0.100 r4 = 35.101 d4 = 4.695 N3 = 1.49310 &ngr;3 = 83.58 r5 = 120.463 d5 = 1.000˜20.900˜ 28.705 r6 = 70.488 d6 = 0.800 N4 = 1.78831 &ngr;4 = 47.32 r7 = 8.526 d7 = 5.198 r8 = −90.436 d8 = 0.800 N5 = 1.75450 &ngr;5 = 51.57 r9 = −785.404 d9 = 2.674 N6 = 1.84666 &ngr;6 = 23.82 r10 = −17.628 d10 = 0.515 r11 = −14.870 d11 = 0.800 N7 = 1.48749 &ngr;7 = 70.44 r12 = 45.809 d12 = 1.366 r13 = −26.330 d13 = 1.344 N8 = 1.84666 &ngr;8 = 23.82 r14* = −30.311 d14 = 23.018˜5.870˜ 1.000 r15 = ∞(ST) d15 = 0.800 r16 = 11.633 d16 = 2.165 N9 = 1.80420 &ngr;9 = 46.50 r17 = 78.024 d17 = 4.756 r18 = −96.322 d18 = 1.561 N10 = 1.75450 &ngr;10 = 51.57 r19 = −14.086 d19 = 0.800 N11 = 1.84666 &ngr;11 = 23.82 r20* = 20.484 d20 = 0.155 r21 = 10.937 d21 = 2.506 N12 = 1.48749 &ngr;12 = 70.44 r22* = −29.274 d22 = 2.186 r23 = 90.101 d23 = 1.374 N13 = 1.79850 &ngr;13 = 22.60 r24 = −61.263 d24 = 1.000˜4.206˜ 1.000 r25 = 29.977 d25 = 0.800 N14 = 1.85000 &ngr;14 = 40.04 r26 = 10.683 d26 = 3.356 r27 = 11.252 d27 = 1.235 N15 = 1.79850 &ngr;15 = 22.60 r28 = 13.786 d28 = 1.399˜3.217˜ 16.734 r29 = 22.159 d29 = 1.546 N16 = 1.79850 &ngr;16 = 22.60 r30 = 89.583 d30 = 1.176 r31 = ∞ d31 = 3.000 N17 = 1.51680 &ngr;17 = 64.20 r32 = ∞ Aspherical Surface Data of Surface r14 &egr; = 1.0000, A4 = −0.55658 × 10−4, A6 = −0.18456 × 10−6, A8 = −0.60664 × 10−8 Aspherical Surface Data of Surface r20 &egr; = 1.0000, A4 = 0.28248 × 10−3, A6 = 0.17454 × 10−5, A8 = 0.32532 × 10−7 Aspherical Surface Data of Surface r22 &egr; = 1.0000

[0092] 4 TABLE 4 Construction Data of Example 4 f = 7.4˜35.9˜49.6, FNO = 2.88˜3.04˜3.63 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 60.590 d1 = 1.200 N1 = 1.84666 &ngr;1 = 23.82 r2 = 47.616 d2 = 5.549 N2 = 1.49310 &ngr;2 = 83.58 r3 = 603.843 d3 = 0.100 r4 = 39.319 d4 = 4.325 N3 = 1.49310 &ngr;3 = 83.58 r5 = 105.185 d5 = 1.000˜32.186˜ 36.134 r6 = 50.395 d6 = 0.800 N4 = 1.85000 &ngr;4 = 40.04 r7 = 8.808 d7 = 5.350 r8 = −22.935 d8 = 0.800 N5 = 1.85000 &ngr;5 = 40.04 r9 = 16.429 d9 = 5.107 N6 = 1.71736 &ngr;6 = 29.50 r10 = −17.500 d10 = 0.100 r11* = 54.395 d11 = 2.000 N7 = 1.84506 &ngr;7 = 23.66 r12 = 1000.000 d12 = 1.278 r13 = −19.690 d13 = 0.800 N8 = 1.75450 &ngr;8 = 51.57 r14 = −77.927 d14 = 22.063˜ 4.444˜1.300 r15 = ∞(ST) d15 = 0.800 r16 = 12.783 d16 = 2.898 N9 = 1.85000 &ngr;9 = 40.04 r17 = 105.738 d17 = 3.453 r18* = 37.506 d18 = 2.226 N10 = 1.84506 &ngr;10 = 23.66 r19 = 9.939 d19 = 1.104 r20 = 12.962 d20 = 4.135 N11 = 1.69680 &ngr;11 = 55.43 r21 = −8.915 d21 = 0.800 N12 = 1.84666 &ngr;12 = 23.82 r22 = 26007.802 d22 = 1.396 r23 = 186.617 d23 = 2.183 N13 = 1.83350 &ngr;13 = 21.00 r24 = −21.147 d24 = 1.810˜6.450˜ 1.000 r25 = 38.703 d25 = 0.800 N14 = 1.85000 &ngr;14 = 40.04 r26 = 13.436 d26 = 4.085 r27 = 14.114 d27 = 1.362 N15 = 1.83350 &ngr;15 = 21.00 r28 = 18.526 d28 = 1.000˜5.337˜ 17.559 r29 = 16.513 d29 = 1.967 N16 = 1.48749 &ngr;16 = 70.44 r30 = 44.597 d30 = 1.479 r31 = ∞ d31 = 3.000 N17 = 1.51680 &ngr;17 = 64.20 r32 = ∞ Aspherical Surface Data of Surface r11 &egr; = 1.0000, A4 = 0.40063 × 10−4, A6 = 0.39528 × 10−6, A8 = −0.29922 × 10−8 Aspherical Surface Data of Surface r18 &egr; = 1.0000, A4 = −0.11545 × 10−3, A6 = −0.96168 × 106, A8 = 0.16989 × 10−7

[0093] 5 TABLE 5 Construction Data of Example 5 f = 8.9˜33.7˜84.8, FNO = 2.43˜3.17˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 171.427 d1= 1.497 N1 = 1.84666 &ngr;1 = 23.82 r2 = 114.665 d2 = 6.918 N2 = 1.49310 &ngr;2 = 83.58 r3 = −850.123 d3 = 0.100 r4 = 96.816 d4 = 4.523 N3 '2 1.49310 &ngr;3 = 83.58 r5 = 348.049 d5 = 2.486˜40.898˜ 95.614 r6* = 24.483 d6 = 2.000 N4 = 1.75450 &ngr;4 = 51.57 r7 = 12.754 d7 = 11.729 r8 = −33.584 d8 = 0.800 N5 = 1.52208 &ngr;5 = 65.92 r9 = 21.063 d9 = 4.926 N6 = 1.84705 &ngr;6 = 25.00 r10 = 281.045 d10 = 0.838 r11 = −40.184 d11 = .800 7 = 1.74495 7 = 24.47 r12 = 99.136 d12 = 41.883˜2.565˜ 1.250 r13 = ∞(ST) d13 = 1.500 r14 = 12.436 d14 = 3.485 N8 = 1.75450 &ngr;v = 51.57 r15 = −172.448 d15 = 1.166 r16 = 375.028 d16 = 0.800 N9 = 1.71675 &ngr;9 '2 26.91 r17 = 30.185 d17 = 1.000˜1.169˜ 1.244 r18* = 16.888 d18 = 1.922 N10 = 1.84666 &ngr;10 = 23.82 r19 = 11.475 d19 = 1.988˜11.017˜ 23.820 r20* = 25.613 d20 = 0.800 N11 = 1.75000 &ngr;11 = 25.14 r21 = 14.963 d21 = 0.077 r22 = 15.312 d22 = 1.202 N12 = 1.75450 &ngr;12 = 51.57 r23 = 16.980 d23 = 0.356 r24 = 16.249 d24 = 6.391 N13 = 1.49310 &ngr;13 = 83.58 r25 = −22.015 d25 = 1.962 r26 = −13.823 d26 = 3.437 N14 = 1.84666 &ngr;14 = 23.82 r27 = −14.151 d27 = 2.000˜12.427˜ 6.704 r28* = 20.728 d28 = 2.834 N15 = 1.52510 &ngr;15 = 56.38 r29 = 15.822 d29 = 1.307 r30 = ∞ d30 = 3.000 N16 = 1.51680 &ngr;16 = 64.20 r31 = ∞ Aspherical Surface Data of Surface r6 &egr; = 1.0000, A4 = 0.66358 × 10−5, A6 = 0.71481 × 10−9, A8 = 0.49766 × 10−10 Aspherical Surface Data of Surface r18 &egr; = 1.0000, A4 = −0.10218 × 10−3, A6 = −0.12797 × 10−5, A8 = 0.10173 × 10−7, A10 = −0.34395 × 10−9 Aspherical Surface Data of Surface r20 &egr; = 1.0000, A4 = −0.34705 × 10−4, A6 = 0.10595 × 10−6, A8 = −0.43764 × 10−8, A10 = 0.17721 × 10−10 Aspherical Surface Data of Surface r28 &egr; = 1.0000, A4 = −0.59570 × 10−5, A6 = −0.55853 × 10−6, A8 = 0.11878 × 10−7, A10 = −0.14101 × 10−9

[0094] 6 TABLE 6 Construction Data of Example 6 f = 7.1˜53.0˜68.6, FNO = 2.55˜3.60˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 81.309 d1 = 1.400 N1 = 1.84666 &ngr;1 = 23.86 r2 = 63.920 d2 = 4.957 N2 = 1.49310 &ngr;2 = 83.58 r3 = −2566.999 d3 = 0.100 r4 = 72.424 d4 = 2.914 N3 = 1.49310 &ngr;3 = 83.58 r5 = 204.372 d5 = 0.900˜54.218˜ 57.909 r6* = −2187.849 d6 = 1.200 N4 = 1.77250 &ngr;4 = 49.77 r7* = 14.815 d7 = 8.614 r8 = −22.207 d8 = 1.500 N5 = 1.84668 &ngr;5 = 23.86 r9 = −39.485 d9 = 0.100 r10 = 528.712 d10 = 4.283 N6 = 1.84666 &ngr;6 = 23.82 r11 = −27.851 d11 = 1.412 r12 = −19.591 d12 = 1.000 N7 = 1.49310 &ngr;7 = 83.58 r13 = −80.805 d13 = 40.111˜ 0.619˜0.100 r14 = ∞(ST) d14 = 1.200 r15* = 20.034 d15 = 3.327 N8 = 1.77112 &ngr;v = 48.87 r16 = 2658.231 d16 = 0.100 r17 = 24.453 d17 = 1.028 N9 = 1.61287 &ngr;9 = 33.36 r18* = 9.473 d18 = 0.432 r19 = 12.678 d19 = 2.612 N10 = 1.75450 &ngr;10 = 51.57 r20 = −167.012 d20 = 0.537˜1.270˜ 1.348 r21 = −32.395 d21 = 6.981 N11 = 1.64379 &ngr;11 = 56.31 r22 = −11.929 d22 = 0.100 r23* = −13.515 d23 = 1.708 N12 = 1.63456 &ngr;12 = 31.17 r24* = 24.372 d24 = 0.263˜ 19.944˜27.790 r25 = 19.740 d25 = 4.770 N13 = 1.79850 &ngr;13 = 22.60 r26 = 13.053 d26 = 0.100 r27 = 13.309 d27 = 5.694 N14 = 1.68636 &ngr;14 = 54.20 r28 = −129.207 d28 = 4.148˜5.575˜ 2.763 r29 = ∞ d29 = 3.000 N15 = 1.51680 &ngr;15 = 64.20 r32 = ∞ Aspherical Surface Data of Surface r6 &egr; = 1.0000, A4 = 0.29074 × 10−4, A6 = −0.89940 × 10−7, A8 = 0.16625 × 10−9 Aspherical Surface Data of Surface r7 &egr; = 1.0000, A4 = 0.44003 × 10−5, A6 = 0.99743 × 10−8, A8 = = −0.48301 × 10−9 Aspherical Surface Data of Surface r15 &egr; = 1.0000, A4 = 0.11178 × 10−3, A6 = 0.10605 × 10−5, A8 = −0.21375 × 10−7, A10 = 0.22240 × 10−9 Aspherical Surface Data of Surface r18 &egr; = 1.0000, A4 = −0.24094 × 10−3, A6 = 0.11663 × 10−5, A8 = −0.57504 × 10−7, A10 = 0.66415 × 10−9 Aspherical Surface Data of Surface r23 &egr; = 1.0000, A4 = 0.12224 × 10−3, A6 = −0.66295 × 10−5, A8 = 0.74249 × 10−7 Aspherical Surface Data of Surface r24 &egr; = 1.0000, A4 = 0.29363 × 10−3, A6 = −0.57030 × 10−5, A8 = 0.80185 × 10−7

[0095] 7 TABLE 8 Construction Data of Example 8 f = 7.5˜45.0˜71.5, FNO = 2.17˜2.89˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 65.664 d1 = 1.200 N1 = 1.75518 &ngr; = 129.92 r2 = 47.591 d2 = 5.244 N2 = 1.49310 &ngr;2 = 83.58 r3 = 217.318 d3 = 0.100 r4 = 51.066 d4 = 4.398 N3 = 1.49310 &ngr;3 = 83.58 r5 = 185.539 d5 = 1.000˜45.300˜ 49.091 r6 = 45.239 d6 = 0.800 N4 = 1.75450 &ngr;4 = 51.57 r7 = 10.516 d7 = 7.570 r8 = −40.143 d8 = 0.800 N5 = 1.80223 &ngr;5 = 44.75 r9 = 23.630 d9 = 5.046 N6 = 1.79123 &ngr;6 = 22.82 r10 = −18.887 d10 = 0.656 r11 = −15.690 d11 = 0.800 N7 = 1.84666 &ngr;7 = 23.82 r12* = −43.100 d12 = 35.75˜5.453˜ 4.000 r13 = ∞(ST) d13 = 0.800 r14 = 13.866 d14 = 2.194 N8 = 1.78923 &ngr;8 = 46.34 r15 = 74.387 d15 = 5.348 r16 = 13.726 d16 = 3.113 N9 = 1.73284 &ngr;9 = 52.33 r17 = −13.373 d17 = 0.800 N10 = 1.84758 &ngr;10 = 26.81 r18 = 8.964 d18 = 0.100 r19 = 7.206 d19 = 1.439 N11 = 1.52510 &ngr;11 = 56.38 r20* = 14.351 d20 = 2.601 r21 = 21.969 d21 = 1.379 N12 = 1.79850 &ngr;12 = 22.60 r22 = −1723.989 d22 = 1.000˜ 3.838˜2.749 r23 = 342.635 d23 = 0.800 N13 = 1.66384 &ngr;13 = 35.98 r24 = 8.966 d24 = 3.000 r25 = 24.255 d25 = 1.566 N14 = 1.79850 &ngr;14 = 22.60 r26* = 120.635 d26 = 1.000˜5.947˜ 14.698 r27 = 25.459 d27 = 1.667 N15 = 1.79850 &ngr;15 = 22.60 r28 = 884.189 d28 = 1.019 r29 = ∞ d29 = 3.000 N16 = 1.51680 &ngr;16 = 64.20 r30 = ∞ Aspherical Surface Data of Surface r12 &egr; = 1.0000, A4 = −0.28880 × 10−4, A6 = −0.39221 × 10−7, A8 = −0.58769 × 10−9 Aspherical Surface Data of Surface r20 &egr; = 1.0000, A4 = 0.44180 × 10−3, A6 = 0.35794 × 10−5, A8 = 0.93325 × 10−7 Aspherical Surface Data of Surface r26 &egr; = 1.0000, A4 = −0.73523 × 10−4, A6 = −0.60792 × 10−6, A8 = −0.59550 × 10−8

[0096] 8 TABLE 9 Construction Data of Example 9 f = 7.5˜54.0˜86.0, FNO = 2.10˜2.84˜3.60 Radius of Axial Refractive Abbe Curvature Distance Index Number r1 = 90.273 d1 = 1.200 N1 = 1.83304 &ngr;1 = 41.53 r2 = 50.609 d2 = 6.584 N2 = 1.49310 &ngr;2 = 83.58 r3 = 491.903 d3 = 0.100 r4 = 50.212 d4 = 5.970 N3 = 1.49310 &ngr;3 = 83.58 r5 = 293.841 d5 = 1.000˜56.319˜ 60.499 r6 = 53.739 d6 = 0.800 N4 = 1.75450 &ngr;4 = 51.57 r7 = 11.112 d7 = 7.570 r8 = −105.475 d8 = 0.800 N5 = 1.76442 &ngr;5 = 49.91 r9 = 16.958 d9 = 6.473 N6 = 1.77039 &ngr;6 = 23.51 r10 = −22.262 d10 = 0.563 r11 = −19.229 d11 = 0.800 N7 = 1.84666 &ngr;7 = 23.82 r12* = −140.106 d12 = 34.166˜ 4.250˜1.000 r13 = ∞(ST) d13 = 0.800 r14 = 14.098 d14 = 2.180 N8 = 1.83255 &ngr;8 = 41.58 r15 = 75.309 d15 = 4.215 r16 = 13.256 d16 = 3.141 N9 = 1.71070 &ngr;9 = 53.17 r17 = −15.268 d17 = 0.800 N10 = 1.80992 &ngr;10 = 25.83 r18 = 7.879 d18 = 0.274 r19 = 7.000 d19 = 1.461 N11 = 1.52510 &ngr;11 = 56.38 r20* = 13.820 d20 = 3.133 r21 = 21.375 d21 = 1.301 N12 '2+1.79850 &ngr;12 = 22.60 r22 = 2254.283 d22 = 1.000˜ 3.613˜1.086 r23 = 2109.616 d23 = 0.800 N13 = 1.64794 &ngr;13 = 36.7S r24 = 9.838 d24 = 2.907 r25 = 21.069 d25 = 1.316 N14 = 1.79850 &ngr;= 1422.60 r26* = 59.731 d26 = 1.000˜6.745˜ 18.339 r27 = 21.610 d27 = 1.710 N15 = 1.84666 &ngr;15 = 23.82 r28 = 97.515 d28 = 1.154 r29 = ∞ d31 = 3.000 N16 '2 1.51680 &ngr;16 = 64.20 r30 = ∞ Aspherical Surface Data of Surface r12 &egr; = 1.0000, A4 = −0.26006 × 10−4, A6 = −0.12948 × 10−7, A8 = −0.69799 × 10−9 Aspherical Surface Data of Surface r20 &egr; = 1.0000, A4 = 0.39398 × 10−3, A6 = 0.33896 × 10−5, A8 = 0.11071 × 10−6 Aspherical Surface Data of Surface r26 &egr; = 1.0000, A4 = −0.53134 × 10−4, A6 = −0.59377 × 10−6, A8 = 0.30506 × 10−8

[0097] 9 TABLE 10 Focusing Data Focusing Unit: Fourth Lens Unit (Gr4) Shooting Distance (from Object Point to Image Plane): D = 0.5 (m) Movement Distance Movement Direction of Focusing Unit of Focusing Unit: W M T Toward Example 1 0.29 3.717 5.181 Image Plane Example 2 0.144 1.448 3.372 ImagePlane Example 3 0.172 1.360 4.638 ImagePlane Example 4 0.234 3.393 3.349 Image Plane Example 5 0.264 2.549 9.552 Object Example 6 0.163 5.338 7.961 Object Example 7 0.314 1.929 8.601 Image Plane Example 8 0.133 2.754 4.258 Image Plane Example 9 0.155 4.251 5.783 Image Plane

[0098] 10 TABLE 11 Actual Values of Conditional Formulae Conditional Conditional Conditional Conditional Formula (1) Formula (2) Formula (3) Formula (4) f1/ff |f4/fT| D34W/D34T &bgr;W4 Example 1 1.65 0.95 1.00 1.20 Example 2 1.90 0.59 0.26 1.36 Example 3 1.30 0.60 1.00 1.34 Example 4 1.48 0.86 1.81 1.35 Example 5 1.93 0.60 0.80 1.63 Example 6 1.54 0.36 0.40 2.36 Example 7 1.27 0.79 0.37 1.40 Example 8 1.30 0.35 0.36 1.58 Example 9 1.21 0.32 0.92 1.52

Claims

1. An optical device comprising:

a zoom lens system which comprises of a plurality of lens units and which achieves zooming by varying unit-to-unit distances; and

an image sensor for converting an optical image formed by the zoom lens system into an electrical signal,

wherein the zoom lens system comprises at least, from an object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power, and the following conditional formula is fulfilled:

b 1.1<f1/fT<2.5

where

f1 represents a focal length of the first lens unit; and

fT represents a focal length of an entire optical system at a telephoto end.

2. An optical device as claimed in

claim 1,

wherein focusing is achieved by moving the fourth lens unit along an optical axis, and the following conditional formula is additionally fulfilled:

0.3<|f4/fT|<2

where

f4 represents a focal length of the fourth lens unit; and

fT represents the focal length of the entire optical system at the telephoto end.

3. An optical device as claimed in

claim 2,

wherein, as zooming is performed from a wide-angle end to the telephoto end, the first lens unit is moved and a distance between the third lens unit and the fourth lens unit increases from the wide-angle end to a middle-focal-length position and decreases from the middle-focal-length position to the telephoto end.

4. An optical device as claimed in

claim 2 wherein the second lens unit has an aspherical surface.

5. An optical device as claimed in

claim 1,

wherein, as zooming is performed from a wide-angle end to the telephoto end, the first lens unit is moved and a distance between the third lens unit and the fourth lens unit increases from the wide-angle end to a middle-focal-length position and decreases from the middle-focal-length position to the telephoto end.

6. An optical device as claimed in

claim 1 further comprising a low-pass filter, said low-pass filter located between the first lens unit and the image sensor, wherein the low-pass filter adjusts spatial frequency characteristics of the optical image formed by the zoom lens system.

7. An optical device as claimed in

claim 6 wherein the low-pass filter is kept stationary during zooming.

8. An optical device as claimed in

claim 1 wherein the second lens unit has an aspherical surface.

9. An optical device as claimed in

claim 1 wherein the zoom lens system further comprises a fifth lens unit having a positive optical power.

10. An optical device as claimed in

claim 9 wherein the zoom lens system further comprises a sixth lens unit having a negative optical power.

11. An optical device as claimed in

claim 9 wherein the zoom lens system further comprises a sixth lens unit having a positive optical power.

12. A digital camera comprising:

an optical lens device, and

a memory;

wherein said optical lens device comprises a zoom lens system which comprises a plurality of lens units and which achieves zooming by varying unit-to-unit distances; and an image sensor for converting an optical image formed by the zoom lens system into an electrical signal;

wherein the zoom lens system comprises at least, from an object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power, and the following conditional formula is fulfilled:

1.1<f1/fT<2.5

where

f1 represents a focal length of the first lens unit; and

fT represents a focal length of an entire optical system at a telephoto end; and

wherein said memory is adapted for storing image data from said image sensor, and said memory is not removable from said digital camera.

13. A digital camera as claimed in

claim 12 wherein the following conditional formula is fulfilled:

0.3<|f4/fT|<2

where

f4 represents a focal length of the fourth lens unit; and

fT represents the focal length of the entire optical system at the telephoto end.

14. An optical device comprising:

a zoom lens system which comprises of a plurality of lens units and which achieves zooming by varying unit-to-unit distances; and

an image sensor for converting an optical image formed by the zoom lens system into an electrical signal,

wherein the zoom lens system comprises at least, from an object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power, the first lens unit being moved as zooming is performed, and

wherein the following conditional formula is fulfilled:

0.3<D34W/D34T<2.5

where

D34W represents an aerial distance between the third lens unit and the fourth lens unit at a wide-angle end; and

D34T represents an aerial distance between the third lens unit and the fourth lens unit at a telephoto end.

15. An optical device as claimed in

claim 14,

wherein, as zooming is performed from the wide-angle end to the telephoto end, the fourth lens unit is moved toward the object side.

16. An optical device as claimed in

claim 15,

wherein, as zooming is performed from the wide-angle end to the telephoto end, a distance between the third lens unit and the fourth lens unit increases from the wide-angle end to a middle-focal-length position and decreases from the middle-focal-length position to the telephoto end.

17. An optical device as claimed

claim 15,

wherein focusing is achieved by moving the fourth lens unit along an optical axis, and the following conditional formula is additionally fulfilled.

0.5<&bgr;W4<2

where

&bgr;W4 represents a lateral magnification of the fourth lens unit at the wide-angle end.

18. An optical device as claimed in

claim 14,

wherein, as zooming is performed from the wide-angle end to the telephoto end, a distance between the third lens unit and the fourth lens unit increases from the wide-angle end to a middle-focal-length position and decreases from the middle-focal-length position to the telephoto end.

19. An optical device as claimed

claim 18,

wherein focusing is achieved by moving the fourth lens unit along an optical axis, and the following conditional formula is additionally fulfilled:

0.5<&bgr;W4<2

where

&bgr;W4 represents a lateral magnification of the fourth lens unit at the wide-angle end.

20. An optical device as claimed

claim 14,

wherein focusing is achieved by moving the fourth lens unit along an optical axis, and the following conditional formula is additionally fulfilled:

0.5<&bgr;W4<2

where

&bgr;W4 represents a lateral magnification of the fourth lens unit at the wide-angle end.

21. An optical device as claimed in

claim 14 wherein the zoom lens system further comprises a fifth lens unit having a positive optical power.

22. An optical device as claimed in

claim 21 wherein the zoom lens system further comprises a sixth lens unit having a negative optical power.

23. An optical device as claimed in

claim 21 wherein the zoom lens system further comprises a sixth lens unit having a positive optical power.

24. A digital camera comprising:

an optical lens device, and

a memory;

wherein said optical lens device comprises a zoom lens system which comprises a plurality of lens units and which achieves zooming by varying unit-to-unit distances; and an image sensor for converting an optical image formed by the zoom lens system into an electrical signal;

wherein the zoom lens system comprises at least, from an object side thereof to an image side thereof, a first lens unit having a positive optical power, a second lens unit having a negative optical power, a third lens unit having a positive optical power, and a fourth lens unit having a negative optical power, the first lens unit being moved as zooming is performed, and wherein the following conditional formula is fulfilled:

0.3<D34W/D34T<2.5

where

D34W represents an aerial distance between the third lens unit and the fourth lens unit at a wide-angle end; and

D34T represents an aerial distance between the third lens unit and the fourth lens unit at a telephoto end; and

wherein said memory is adapted for storing image data from said image sensor, and said memory is not removable from said digital camera.

25. A digital camera as claimed in

claim 24 wherein the following conditional formula is fulfilled:

0.5<&bgr;W4<2

where

&bgr;W4 represents a lateral magnification of the fourth lens unit at the wide-angle end.