Taking lens device

Abstract

A taking lens device has a zoom lens system having an optical 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. At least one of the following conditional formula is fulfilled: 1.1

Description

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

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

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.

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).

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

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.

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 <f 1 /fT< 2.5

where

f 1 represents the focal length of the first lens unit; and

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

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 <D 34W /D 34T <2.5

where

D 34W represents the aerial distance between the third lens unit and the fourth lens unit at the wide-angle end; and

D 34T represents the aerial distance between the third lens unit and the fourth lens unit at the telephoto end.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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.

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.

In all of the embodiments, the zoom lens system includes, from the object side, a first lens unit Gr 1 having a positive optical power, a second lens unit Gr 2 having a negative optical power, a third lens unit Gr 3 having a positive optical power, and a fourth lens unit Gr 4 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 Gr 3 includes an aperture stop ST at the object-side end thereof.

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 Gr 1 having a positive optical power, a second lens unit Gr 2 having a negative optical power, a third lens unit Gr 3 having a positive optical power, and a fourth lens unit Gr 4 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 Gr 1 having a positive optical power, a second lens unit Gr 2 having a negative optical power, a third lens unit Gr 3 having a positive optical power, a fourth lens unit Gr 4 having a negative optical power, and a fifth lens unit Gr 5 having a positive optical power.

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 Gr 1 having a positive optical power, a second lens unit Gr 2 having a negative optical power, a third lens unit Gr 3 having a positive optical power, a fourth lens unit Gr 4 having a negative optical power, a fifth lens unit Gr 5 having a positive optical power, and a sixth lens unit Gr 6 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 Gr 1 having a positive optical power, a second lens unit Gr 2 having a negative optical power, a third lens unit Gr 3 having a positive optical power, a fourth lens unit Gr 4 having a negative optical power, a fifth lens unit Gr 5 having a positive optical power, and a sixth lens unit Gr 6 having a positive optical power.

In 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 Gr 3 , Gr 4 have positive powers, a configuration starting with a positive-negative-positive-negative sequence, in which the fourth lens unit Gr 4 is negative, the opposite signs of the optical powers of the third lens unit and the fourth lens unit Gr 3 , Gr 4 permit a high zoom ratio to be achieved with those lens units Gr 3 , Gr 4 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.

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 <f 1 /fT< 2.5  (1)

where

f 1 represents the focal length of the first lens unit Gr 1 ; and

fT represents the focal length of the entirety of the optical system of the zoom lens system at the telephoto end T.

If the lower limit of conditional formula (1) were to be transgressed, the optical power of the first lens unit Gr 1 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 Gr 1 would be too weak, and thus it would be difficult to achieve satisfactory compactness, in particular, at the telephoto end T.

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 Gr 4 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 <|f 4 /fT|< 2  (2)

where

f 4 represents the focal length of the fourth lens unit Gr 4 ; and

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

As conditional formula (2) suggests, the fourth lens unit Gr 4 has a relatively weak optical power, and accordingly the fourth lens unit Gr 4 has the fewest lens elements. Thus, focusing is best achieved by moving (as indicated by the arrow mF) the fourth lens unit Gr 4 , 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.

If the lower limit of conditional formula (2) were to be transgressed, the optical power of the fourth lens unit Gr 4 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 Gr 4 would be so weak that the fourth lens unit Gr 4 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.

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 Gr 1 be moved and the distance between the third and fourth lens units Gr 3 , Gr 4 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.

Conventionally, the majority of optical systems used in video cameras or digital cameras are so constructed that their first lens unit Gr 1 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 Gr 1 movable. By moving the first lens unit Gr 1 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 Gr 2 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 Gr 3 , Gr 4 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 field that occurs in the middle-focal-length region. This makes it possible to realize a high-zoom-ratio zoom lens system.

It is preferable to dispose, as in all of the embodiments, an aspherical surface in the second lens unit Gr 2 . Disposing an aspherical surface in the second lens unit Gr 2 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 Gr 2 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 Gr 2 .

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 Gr 1 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 <D 34W /D 34T <2.5  (3)

where

D 34W represents the aerial distance between the third lens unit and the fourth lens unit Gr 3 , Gr 4 at the wide-angle end W; and

D 34T represents an aerial distance between the third lens unit and the fourth lens unit Gr 3 , Gr 4 at the telephoto end T.

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 Gr 3 , Gr 4 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 Gr 3 , Gr 4 at the wide-angle end W is so long that it would be difficult to achieve satisfactory compactness at the wide-angle end W.

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 Gr 1 be moved as described previously and, in addition, that the fourth lens unit Gr 4 be moved toward the object side. This makes it possible to obtain a higher zoom ratio in the fourth lens unit Gr 4 , 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.

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 Gr 3 , Gr 4 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 Gr 3 , Gr 4 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.

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 Gr 4 , 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<β W4 <2  (4)

where

β W4 represents the lateral magnification of the fourth lens unit Gr 4 at the wide-angle end W.

As described previously, the fourth lens unit Gr 4 has a relatively weak optical power, and accordingly the fourth lens unit Gr 4 has the fewest lens elements. Thus, the fourth lens unit Gr 4 , 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.

If the lower limit of conditional formula (4) were to be transgressed, the zoom ratio distributed to the fourth lens unit Gr 4 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 Gr 3 . As a result, it would be difficult to eliminate the aberrations that would occur in the third lens unit Gr 3 . By contrast, if the upper limit of conditional formula (4) were to be transgressed, the zoom ratio distributed to the fourth lens unit Gr 4 would be so high that it would be difficult to eliminate the aberrations that would occur in the fourth lens unit Gr 4 . As a result, it would be impossible to realize a compact zoom lens system.

As described earlier, disposing an aspherical surface in the second lens unit Gr 2 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 Gr 2 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 Gr 2 .

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.

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 Gr 1 stationary during zooming, and disposing a mirror behind the first lens unit Gr 1 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.

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

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.

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 νi (i=1, 2, 3, . . . ) represent the refractive index Nd for the d-line and the Abbe number (νd) 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 Gr 4 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.

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 are also listed in their respective construction data.

X ( H )=( C 0 ·H 2 )/( 1+{square root over (1−ε· C 0 2 ·H 2 +L )})

+( A 4 ·H 4 +A 6 ·H 6 +A 8 ·H 8 +A 10 ·H 10 )  (AS)

where

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

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

C0 represents the paraxial curvature (the reciprocal of the radius of curvature);

ε represents the quadric surface parameter; and

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

FIGS. 10A-10I , 11 A- 11 I, 12 A- 12 I, 13 A- 13 I, 14 A- 14 I, 15 A- 15 I, 16 A- 16 I, 17 A- 17 I, and 18 A- 18 I are diagrams showing the aberration observed in Examples 1 to 9, respectively, when focused at infinity. FIGS. 19A-19F , 20 A- 20 F, 21 A- 21 F, 22 A- 22 F, 23 A- 23 F, 24 A- 24 F, and 25 A- 25 F 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 , 11 A- 11 C, 12 A- 12 C, 13 A- 13 C, 14 A- 14 C, 15 A- 15 C, 16 A- 16 C, 17 A- 17 C, 18 A- 18 C, 19 A- 19 C, 20 A- 20 C, 21 A- 21 C, 22 A- 22 C, 23 A- 23 C, 24 A- 24 C, and 25 A- 25 C show the aberration observed at the wide-angle end W, FIGS. 10D-10F , 11 D- 11 F, 12 D- 12 F, 13 D- 13 F, 14 D- 14 F, 15 D- 15 F, 16 D- 16 F, 17 D- 17 F, and 18 D- 18 F show the aberration observed in the middle position M, and 10 G- 10 I, 11 G- 11 I, 12 G- 12 I, 13 G- 13 I, 14 G- 14 I, 15 G- 15 I, 16 G- 16 I, 17 G- 17 I, 18 G- 18 I, 19 D- 19 F, 20 D- 20 F, 21 D- 21 F, 22 D- 22 F, 23 D- 23 F, 24 D- 24 F, and 25 D- 25 F show the aberration observed at the telephoto end T. Of these diagrams, FIGS. 10A , 10 D, 10 G, 11 A, 11 D, 11 G, 12 A, 12 D, 12 G, 13 A, 13 D, 13 G, 14 A, 14 D, 14 G, 15 A, 15 D, 15 G, 16 A, 16 D, 16 G, 17 A, 17 D, 17 G, 18 A, 18 D, 18 G, 19 A, 19 D, 20 A, 20 D, 21 A, 21 D, 22 A, 22 D, 23 A, 23 D, 24 A, 24 D, 25 A, and 25 D show spherical aberration, FIGS. 10B , 10 E, 10 H, 11 B, 11 E, 11 H, 12 B, 12 E, 12 H, 13 B, 13 E, 13 H, 14 B, 14 E, 14 H, 15 B, 15 E, 15 H, 16 B, 16 E, 16 H, 17 B, 17 E, 17 H, 18 B, 18 E, 18 H, 19 B, 19 E, 20 B, 20 E, 21 B, 21 E, 22 B, 22 E, 23 B, 23 E, 24 B, 24 E, 25 B, and 25 E show astigmatism, and FIGS. 10C , 10 F, 10 I, 11 C, 11 F, 11 I, 12 C, 12 F, 12 I, 13 C, 13 F, 13 I, 14 C, 14 F, 14 I, 15 C, 15 F, 15 I, 16 C, 16 F, 16 I, 17 C, 17 F, 17 I, 18 C, 18 F, 18 I, 19 C, 19 F, 20 C, 20 F, 21 C, 21 F, 22 C, 22 F, 23 C, 23 F, 24 C, 24 F, 25 C, and 25 F 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.

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	ν1 = 28.26
r2 = 46.105
	d2 = 4.909	N2 = 1.49310	ν2 = 83.58
r3 = 557.712
	d3 = 0.100
r4 = 41.139
	d4 = 3.518	N3 = 1.49310	ν3 = 83.58
r5 = 95.433
	d5 = 1.000˜28.553˜
	40.964
r6 = 28.766
	d6 = 0.800	N4 = 1.80420	ν4 = 46.50
r7 = 8.145
	d7 = 6.254
r8 = −24.683
	d8 = 0.800	N5 = 1.80741	ν5 = 31.59
r9 = 408.759
	d9 = 2.972	N6 = 1.84666	ν6 = 23.82
r10 = −15.616
	d10 = 0.727
r11 = −12.222
	d11 = 0.800	N7 = 1.52510	ν7 = 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	ν8 = 47.32
r15 = 212.313
	d15 = 5.251
r16 = −66.079
	d16 = 1.795	N9 = 1.48749	ν9 = 70.44
r17 = −10.997
	d17 = 0.800	N10 = 1.84666	ν10 = 23.82
r18* = 29.156
	d18 = 0.100
r19 = 12.934
	d19 = 3.092	N11 = 1.48749	ν11 = 70.44
r20* = −19.433
	d20 = 0.100
r21 = −788.619
	d21 = 4.662	N12 = 1.79850	ν12 = 22.60
r22 = −27.115
	d22 = 1.000˜7.000˜
	1.000
r23 = 23.066
	d23 = 0.800	N13 = 1.85000	ν13 = 40.04
r24 = 11.361
	d24 = 3.500
r25 = 11.740
	d25 = 1.826	N14 = 1.79850	ν14 = 22.60
r26 = 14.538
	d26 = 2.381˜2.000˜
	13.578
r27 = ∞
	d27 = 3.000	N15 = 1.51680	ν15 = 64.20
r28 = ∞
Aspherical Surface Data of Surface r12
ε = 1.0000, A4 = −0.90791 × 10 −4 , A6 = −0.27514 × 10 −6 , A8 = −0.37035 × 10 −8
Aspherical Surface Data of Surface r18
ε = 1.0000, A4 = 0.28853 × 10 −3 , A6 = 0.12716 × 10 −5 , A8 = 0.10778 × 10 −7
Aspherical Surface Data of Surface r20
ε = 1.0000

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	ν1 = 22.60
r2 = 50.059
	d2 = 3.893	N2 = 1.49310	ν2 = 83.58
r3 = 264.139
	d3 = 0.100
r4 = 57.561
	d4 = 2.818	N3 = 1.49310	ν3 = 83.58
r5 = 155.066
	d5 = 1.000˜30.739˜
	48.448
r6 = 29.965
	d6 = 0.800	N4 = 1.75450	ν4 = 51.57
r7 = 9.032
	d7 = 7.570
r8 = −52.559
	d8 = 0.800	N5 = 1.75450	ν5 = 51.57
r9 = 21.530
	d9 = 4.134	N6 = 1.79850	ν6 = 22.60
r10 = −18.800
	d10 = 0.486
r11 = −15.910
	d11 = 0.800	N7 = 1.84666	ν7 = 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	ν8 = 35.43
r15 = 84.611
	d15 = 3.644
r16 = 15.627
	d16 = 2.756	N9 = 1.75450	ν9 = 51.57
r17 = −12.357
	d17 = 0.800	N10 = 1.84666	ν10 = 23.82
r18 = 9.111
	d18 = 0.100
r19 = 7.143
	d19 = 1.343	N11 = 1.52510	ν11 = 56.38
r20* = 13.828
	d20 = 2.118
r21 = 31.671
	d21 = 1.530	N12 = 1.79850	ν12 = 22.60
r22 = −35.431
	d22 = 1.000˜5.669˜
	4.095
r23 = 26.961
	d23 = 0.800	N13 = 1.85000	ν13 = 40.04
r24 = 9.331
	d24 = 2.307
r25 = 11.028
	d25 = 1.289	N14 = 1.79850	ν14 = 22.60
r26 = 14.503
	d26 = 2.123˜2.989˜
	8.644
r27 = −130.604
	d27 = 1.347	N15 = 1.79850	ν15 = 22.60
r28 = −33.480
	d28 = 0.858
r29 = ∞
	d29 = 3.000	N16 = 1.51680	ν16 = 64.20
r30 = ∞
Aspherical Surface Data of Surface r12
ε = 1.0000, A4 = −0.44023 × 10 −4 , A6 = −0.52908 × 10 −7 , A8 = −0.21921 × 10 −8
Aspherical Surface Data of Surface r20
ε = 1.0000, A4 = 0.52117 × 10 −3 , A6 = 0.41505 × 10 −5 , A8 = 0.98968 × 10 −7

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	ν1 = 22.60
r2 = 49.435
	d2 = 4.655	N2 = 1.49310	ν2 = 83.58
r3 = 579.022
	d3 = 0.100
r4 = 35.101
	d4 = 4.695	N3 = 1.49310	ν3 = 83.58
r5 = 120.463
	d5 = 1.000˜20.900˜
	28.705
r6 = 70.488
	d6 = 0.800	N4 = 1.78831	ν4 = 47.32
r7 = 8.526
	d7 = 5.198
r8 = −90.436
	d8 = 0.800	N5 = 1.75450	ν5 = 51.57
r9 = −785.404
	d9 = 2.674	N6 = 1.84666	ν6 = 23.82
r10 = −17.628
	d10 = 0.515
r11 = −14.870
	d11 = 0.800	N7 = 1.48749	ν7 = 70.44
r12 = 45.809
	d12 = 1.366
r13 = −26.330
	d13 = 1.344	N8 = 1.84666	ν8 = 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	ν9 = 46.50
r17 = 78.024
	d17 = 4.756
r18 = −96.322
	d18 = 1.561	N10 = 1.75450	ν10 = 51.57
r19 = −14.086
	d19 = 0.800	N11 = 1.84666	ν11 = 23.82
r20* = 20.484
	d20 = 0.155
r21 = 10.937
	d21 = 2.506	N12 = 1.48749	ν12 = 70.44
r22* = −29.274
	d22 = 2.186
r23 = 90.101
	d23 = 1.374	N13 = 1.79850	ν13 = 22.60
r24 = −61.263
	d24 = 1.000˜4.206˜
	1.000
r25 = 29.977
	d25 = 0.800	N14 = 1.85000	ν14 = 40.04
r26 = 10.683
	d26 = 3.356
r27 = 11.252
	d27 = 1.235	N15 = 1.79850	ν15 = 22.60
r28 = 13.786
	d28 = 1.399˜3.217˜
	16.734
r29 = 22.159
	d29 = 1.546	N16 = 1.79850	ν16 = 22.60
r30 = 89.583
	d30 = 1.176
r31 = ∞
	d31 = 3.000	N17 = 1.51680	ν17 = 64.20
r32 = ∞
Aspherical Surface Data of Surface r14
ε = 1.0000, A4 = −0.55658 × 10 −4 , A6 = −0.18456 × 10 −6 , A8 = −0.60664 × 10 −8
Aspherical Surface Data of Surface r20
ε = 1.0000, A4 = 0.28248 × 10 −3 , A6 = 0.17454 × 10 −5 , A8 = 0.32532 × 10 −7
Aspherical Surface Data of Surface r22
ε = 1.0000

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	ν1 = 23.82
r2 = 47.616
	d2 = 5.549	N2 = 1.49310	ν2 = 83.58
r3 = 603.843
	d3 = 0.100
r4 = 39.319
	d4 = 4.325	N3 = 1.49310	ν3 = 83.58
r5 = 105.185
	d5 = 1.000˜32.186˜
	36.134
r6 = 50.395
	d6 = 0.800	N4 = 1.85000	ν4 = 40.04
r7 = 8.808
	d7 = 5.350
r8 = −22.935
	d8 = 0.800	N5 = 1.85000	ν5 = 40.04
r9 = 16.429
	d9 = 5.107	N6 = 1.71736	ν6 = 29.50
r10 = −17.500
	d10 = 0.100
r11* = 54.395
	d11 = 2.000	N7 = 1.84506	ν7 = 23.66
r12 = 1000.000
	d12 = 1.278
r13 = −19.690
	d13 = 0.800	N8 = 1.75450	ν8 = 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	ν9 = 40.04
r17 = 105.738
	d17 = 3.453
r18* = 37.506
	d18 = 2.226	N10 = 1.84506	ν10 = 23.66
r19 = 9.939
	d19 = 1.104
r20 = 12.962
	d20 = 4.135	N11 = 1.69680	ν11 = 55.43
r21 = −8.915
	d21 = 0.800	N12 = 1.84666	ν12 = 23.82
r22 = 26007.802
	d22 = 1.396
r23 = 186.617
	d23 = 2.183	N13 = 1.83350	ν13 = 21.00
r24 = −21.147
	d24 = 1.810˜6.450˜
	1.000
r25 = 38.703
	d25 = 0.800	N14 = 1.85000	ν14 = 40.04
r26 = 13.436
	d26 = 4.085
r27 = 14.114
	d27 = 1.362	N15 = 1.83350	ν15 = 21.00
r28 = 18.526
	d28 = 1.000˜5.337˜
	17.559
r29 = 16.513
	d29 = 1.967	N16 = 1.48749	ν16 = 70.44
r30 = 44.597
	d30 = 1.479
r31 = ∞
	d31 = 3.000	N17 = 1.51680	ν17 = 64.20
r32 = ∞
Aspherical Surface Data of Surface r11
ε = 1.0000, A4 = 0.40063 × 10 −4 , A6 = 0.39528 × 10 −6 , A8 = −0.29922 × 10 −8
Aspherical Surface Data of Surface r18
ε = 1.0000, A4 = −0.11545 × 10 −3 , A6 = −0.96168 × 10 6 , A8 = 0.16989 × 10 −7

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	ν1 = 23.82
r2 = 114.665
	d2 = 6.918	N2 = 1.49310	ν2 = 83.58
r3 = −850.123
	d3 = 0.100
r4 = 96.816
	d4 = 4.523	N3 = 1.49310	ν3 = 83.58
r5 = 348.049
	d5 = 2.486˜40.898˜
	95.614
r6* = 24.483
	d6 = 2.000	N4 = 1.75450	ν4 = 51.57
r7 = 12.754
	d7 = 11.729
r8 = −33.584
	d8 = 0.800	N5 = 1.52208	ν5 = 65.92
r9 = 21.063
	d9 = 4.926	N6 = 1.84705	ν6 = 25.00
r10 = 81.045
	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	νv = 51.57
r15 = −172.448
	d15 = 1.166
r16 = 375.028
	d16 = 0.800	N9 = 1.71675	ν9 = 26.91
r17 = 30.185
	d17 = 1.000˜1.169˜
	1.244
r18* = 16.888
	d18 = 1.922	N10 = 1.84666	ν10 = 23.82
r19 = 11.475
	d19 = 1.988˜11.017˜
	23.820
r20* = 25.613
	d20 = 0.800	N11 = 1.75000	ν11 = 25.14
r21 = 14.963
	d21 = 0.077
r22 = 15.312
	d22 = 1.202	N12 = 1.75450	ν12 = 51.57
r23 = 16.980
	d23 = 0.356
r24 = 16.249
	d24 = 6.391	N13 = 1.49310	ν13 = 83.58
r25 = −22.015
	d25 = 1.962
r26 = −13.823
	d26 = 3.437	N14 = 1.84666	ν14 = 23.82
r27 = −14.151
	d27 = 2.000˜12.427˜
	6.704
r28* = 20.728
	d28 = 2.834	N15 = 1.52510	ν15 = 56.38
r29 = 15.822
	d29 = 1.307
r30 = ∞
	d30 = 3.000	N16 = 1.51680	ν16 = 64.20
r31 = ∞
Aspherical Surface Data of Surface r6
ε = 1.0000, A4 = 0.66358 × 10 −5 , A6 = 0.71481 × 10 −9 , A8 = 0.49766 × 10 −10
Aspherical Surface Data of Surface r18
ε = 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
ε = 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
ε = 1.0000, A4 = −0.59570 × 10 −5 , A6 = −0.55853 × 10 −6 , A8 = 0.11878 × 10 −7 , A10 = −0.14101 × 10 −9

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	ν1 = 23.86
r2 = 63.920
	d2 = 4.957	N2 = 1.49310	ν2 = 83.58
r3 = −2566.999
	d3 = 0.100
r4 = 72.424
	d4 = 2.914	N3 = 1.49310	ν3 = 83.58
r5 = 204.372
	d5 = 0.900˜54.218˜
	57.909
r6* = −2187.849
	d6 = 1.200	N4 = 1.77250	ν4 = 49.77
r7* = 14.815
	d7 = 8.614
r8 = −22.207
	d8 = 1.500	N5 = 1.84668	ν5 = 23.86
r9 = −39.485
	d9 = 0.100
r10 = 528.712
	d10 = 4.283	N6 = 1.84666	ν6 = 23.82
r11 = −27.851
	d11 = 1.412
r12 = −19.591
	d12 = 1.000	N7 = 1.49310	ν7 = 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	ν8 = 48.87
r16 = 2658.231
	d16 = 0.100
r17 = 24.453
	d17 = 1.028	N9 = 1.61287	ν9 = 33.36
r18* = 9.473
	d18 = 0.432
r19 = 12.678
	d19 = 2.612	N10 = 1.75450	ν10 = 51.57
r20 = −167.012
	d20 = 0.537˜1.270˜
	1.348
r21 = −32.395
	d21 = 6.981	N11 = 1.64379	ν11 = 56.31
r22 = −11.929
	d22 = 0.100
r23* = −13.515
	d23 = 1.708	N12 = 1.63456	ν12 = 31.17
r24* = 24.372
	d24 = 0.263˜
	19.944˜27.790
r25 = 19.740
	d25 = 4.770	N13 = 1.79850	ν13 = 22.60
r26 = 13.053
	d26 = 0.100
r27 = 13.309
	d27 = 5.694	N14 = 1.68636	ν14 = 54.20
r28 = −129.207
	d28 = 4.148˜5.575˜
	2.763
r29 = ∞
	d29 = 3.000	N15 = 1.51680	ν15 = 64.20
r32 = ∞
Aspherical Surface Data of Surface r6
ε = 1.0000, A4 = 0.29074 × 10 −4 , A6 = −0.89940 × 10 −7 , A8 = 0.16625 × 10 −9
Aspherical Surface Data of Surface r7
ε = 1.0000, A4 = 0.44003 × 10 −5 , A6 = 0.99743 × 10 −8 , A8 = = −0.48301 × 10 −9
Aspherical Surface Data of Surface r15
ε = 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
ε = 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
ε = 1.0000, A4 = 0.12224 × 10 −3 , A6 = −0.66295 × 10 −5 , A8 = 0.74249 × 10 −7
Aspherical Surface Data of Surface r24
ε = 1.0000, A4 = 0.29363 × 10 −3 , A6 = −0.57030 × 10 −5 , A8 = 0.80185 × 10 −7

TABLE 7
Construction Data of Example 7
f = 7.1˜49.0, FNO = 2.50˜3.03˜3.66
Radius of	Axial	Refractive	Abbe
Curvature	Distance	Index	Number
r1 = 111.111
	d1= 1.400	N1 = 1.79850	ν1 = 22.60
r2 = 85.390
	d2 = 4.303	N2 = 1.49310	ν2 = 83.58
r3 = −1831.972
	d3 = 0.100
r4 = 43.431
	d4 = 4.988	N3 = 1.49310	ν3 = 83.58
r5 = 130.083
	d5 = 0.900˜24.171˜
	43.681
r6 = 35.035
	d6 = 1.200	N4 = 1.75450	ν4 = 51.57
r7 = 10.040
	d7 = 4.791
r8 = −96.605
	d8 = 1.100	N5 = 1.755450	ν5 = 51.57
r9 = 15.175
	d9 = 1.925
r10* = 25.398
	d10 = 3.981	N6 = 1.84666	ν6 = 23.82
r11* = −43.373
	d11 = 1.258
r12 = −15.932
	d12 = 1.000	N7 = 1.48749	ν7 = 70.44
r13 = −134.899
	d13 = 20.871˜5.426˜
	0.600
r14 = ∞(ST)
	d14 = 0.600
r15 = 11.251
	d15 = 2.129	N8 = 1.755450	ν8 = 51.57
r16 = 422.558
	d16 = 4.585
r17* = −39.509
	d17 = 1.500	N9 = 1.70395	ν9 = 26.41
r18* = 12.891
	d18 = 0.596
r19 = 12.874
	d19 = 2.614	N10 = 1.48749	ν10 = 70.44
r20 = −14.240
	d20 = 1.806˜1.837˜
	3.682
r21 =
−8157.937
	d21 = 0.800	N11 = 1.71649	ν11 = 25.74
r22 = 13.228
	d22 = 0.445
r23 = 13.631
	d23 = 1.919	N12 = 1.48749	ν12 = 70.44
r24 = 668.856
	d24 = 3.002˜1.300˜
	12.240
r25 = 31.322
	d25 = 1.691	N13 = 1.79850	ν13 = 22.60
r26 = −217.261
	d26 = 0.500˜9.743˜
	7.994
r27 = −18.461
	d27 = 4.643	N14 = 1.79850	ν14 = 22.60
r28 = −11.955
	d28 = 0.460	N15 = 1.83724	ν15 = 30.17
r26 = 21.532
	d29 = 0.900
r30 = ∞
	d27 = 3.000	N16 = 1.51680	ν16 = 64.20
r31 = ∞
Aspherical Surface Data of Surface r10
ε = 1.0000, A4 = 0.34767 × 10 −4 , A6 = 0.63939 × 10 −7 , A8 = −0.15659 × 10 −8
Aspherical Surface Data of Surface r11
ε = 1.0000, A4 = −0.11239 × 10 −4 , A6 = −0.50907 × 10 −7 , A8 = 0.20881 × 10 −7 , A10 = −0.34395 × 10 −8
Aspherical Surface Data of Surface r17
ε = 1.0000, A4 = −0.53164 × 10 −3 , A6 = 0.11706 × 10 −4 , A8 = −0.13639 × 10 −8 , A10 = 0.17721 × 10 −6
Aspherical Surface Data of Surface r18
ε = 1.0000, A4 = −0.23930 × 10 −3 , A6 = 0.14046 × 10 −4 , A8 = −0.15638 × 10 −7 , A10 = −0.14101 × 10 −6

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	ν = 129.92
r2 = 47.591
	d2 = 5.244	N2 = 1.49310	ν2 = 83.58
r3 = 217.318
	d3 = 0.100
r4 = 51.066
	d4 = 4.398	N3 = 1.49310	ν3 = 83.58
r5 = 185.539
	d5 = 1.000˜45.300˜
	49.091
r6 = 45.239
	d6 = 0.800	N4 = 1.75450	ν4 = 51.57
r7 = 10.516
	d7 = 7.570
r8 = −40.143
	d8 = 0.800	N5 = 1.80223	ν5 = 44.75
r9 = 23.630
	d9 = 5.046	N6 = 1.79123	ν6 = 22.82
r10 = −18.887
	d10 = 0.656
r11 = −15.690
	d11 = 0.800	N7 = 1.84666	ν7 = 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	ν8 = 46.34
r15 = 74.387
	d15 = 5.348
r16 = 13.726
	d16 = 3.113	N9 = 1.73284	ν9 = 52.33
r17 = −13.373
	d17 = 0.800	N10 = 1.84758	ν10 = 26.81
r18 = 8.964
	d18 = 0.100
r19 = 7.206
	d19 = 1.439	N11 = 1.52510	ν11 = 56.38
r20* = 14.351
	d20 = 2.601
r21 = 21.969
	d21 = 1.379	N12 = 1.79850	ν12 = 22.60
r22 = −1723.989
	d22 = 1.000˜
	3.838˜2.749
r23 = 342.635
	d23 = 0.800	N13 = 1.66384	ν13 = 35.98
r24 = 8.966
	d24 = 3.000
r25 = 24.255
	d25 = 1.566	N14 = 1.79850	ν14 = 22.60
r26* = 120.635
	d26 = 1.000˜5.947˜
	14.698
r27 = 25.459
	d27 = 1.667	N15 = 1.79850	ν15 = 22.60
r28 = 884.189
	d28 = 1.019
r29 = ∞
	d29 = 3.000	N16 = 1.51680	ν16 = 64.20
r30 = ∞
Aspherical Surface Data of Surface r12
ε = 1.0000, A4 = −0.28880 × 10 −4 , A6 = −0.39221 × 10 −7 , A8 = −0.58769 × 10 −9
Aspherical Surface Data of Surface r20
ε = 1.0000, A4 = 0.44180 × 10 −3 , A6 = 0.35794 × 10 −5 , A8 = 0.93325 × 10 −7
Aspherical Surface Data of Surface r26
ε = 1.0000, A4 = −0.73523 × 10 −4 , A6 = −0.60792 × 10 −6 , A8 = −0.59550 × 10 −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	ν1 = 41.53
r2 = 50.609
	d2 = 6.584	N2 = 1.49310	ν2 = 83.58
r3 = 491.903
	d3 = 0.100
r4 = 50.212
	d4 = 5.970	N3 = 1.49310	ν3 = 83.58
r5 = 293.841
	d5 = 1.000˜56.319˜
	60.499
r6 = 53.739
	d6 = 0.800	N4 = 1.75450	ν4 = 51.57
r7 = 11.112
	d7 = 7.570
r8 = −105.475
	d8 = 0.800	N5 = 1.76442	ν5 = 49.91
r9 = 16.958
	d9 = 6.473	N6 = 1.77039	ν6 = 23.51
r10 = −22.262
	d10 = 0.563
r11 = −19.229
	d11 = 0.800	N7 = 1.84666	ν7 = 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	ν8 = 41.58
r15 = 75.309
	d15 = 4.215
r16 = 13.256
	d16 = 3.141	N9 = 1.71070	ν9 = 53.17
r17 = −15.268
	d17 = 0.800	N10 = 1.80992	ν10 = 25.83
r18 = 7.879
	d18 = 0.274
r19 = 7.000
	d19 = 1.461	N11 = 1.52510	ν11 = 56.38
r20* = 13.820
	d20 = 3.133
r21 = 21.375
	d21 = 1.301	N12 '2+1.79850	ν12 = 22.60
r22 = 2254.283
	d22 = 1.000˜
	3.613˜1.086
r23 = 2109.616
	d23 = 0.800	N13 = 1.64794	ν13 = 36.75
r24 = 9.838
	d24 = 2.907
r25 = 21.069
	d25 = 1.316	N14 = 1.79850	ν14 = 22.60
r26* = 59.731
	d26 = 1.000˜6.745˜
	18.339
r27 = 21.610
	d27 = 1.710	N15 = 1.84666	ν15 = 23.82
r28 = 97.515
	d28 = 1.154
r29 = ∞
	d31 = 3.000	N16 = 1.51680	ν16 = 64.20
r30 = ∞
Aspherical Surface Data of Surface r12
ε = 1.0000, A4 = −0.26006 × 10 −4 , A6 = −0.12948 × 10 −7 , A8 = −0.69799 × 10 −9
Aspherical Surface Data of Surface r20
ε = 1.0000, A4 = 0.39398 × 10 −3 , A6 = 0.33896 × 10 −5 , A8 = 0.11071 × 10 −6
Aspherical Surface Data of Surface r26
ε = 1.0000, A4 = −0.53134 × 10 −4 , A6 = −0.59377 × 10 −6 , A8 = 0.30506 × 10 −8

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

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

Claims

1. An optical device comprising:a zoom lens system having an optical 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 wheref1 represents a focal length of the first lens unit; and fT represents a focal length of an entirety of said 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 wheref4 represents a focal length of the fourth lens unit; and fT represents the focal length of the entirety of said 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, having an optical 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 wheref1 represents a focal length of the first lens unit; and fT represents a focal length of an entirety of said 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 wheref4 represents a focal length of the fourth lens unit; and fT represents the focal length of the entirety of said optical system at the telephoto end.

14. An optical device comprising: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 whereD34W 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 in 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<βW4<2 whereβW4 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 in 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<βW4<2 whereβW4 represents a lateral magnification of the fourth lens unit at the wide-angle end.

20. An optical device as claimed in 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<βW4<2 whereβW4 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 whereD34W 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<βW4<2 whereβW4 represents a lateral magnification of the fourth lens unit at the wide-angle end.