Taking lens device

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.

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.

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.

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.

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.

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 )})

+( 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.