Zoom lens and pickup system

The present invention relates to a zoom lens incorporated in pickup apparatuses such as a digital still camera, a TV camera, and a video camera.

Related Background Art

The zoom lens as mentioned above has a four unit structure in which a first lens unit having a positive refractive power for focus adjustment, a second lens unit having a negative refractive power for power-varying, a third lens unit having a positive or negative refractive power for compensating image-plane fluctuation in accordance with the power-varying, and a fourth lens unit having a positive refractive power for forming an image are arranged from the order of an object, or a three unit structure in which the third lens unit has a function of compensating image-plane fluctuation and forming an image.

Of such zoom lenses, in particular, a telescopic-type zoom lenses, each having an angle of view (2ω) not greater than 2.0 degrees at its telephoto end and a variable power ratio of about 1.5 to 3, are disclosed in U.S. Pat. No. 5,442,486, Japanese Patent Laid-Open No. 10-90599, and European Patent Application No. 1092999. Also, a super-telescopic-type zoom lens for use in a TV camera, having an angle of view (2ω) not greater than 2.0 degrees at the telephoto end and a variable power ratio of about 40 is disclosed.

When an object such as an animal or a bird is picked up outdoors at a long range so as to be provided for a TV nature program or the like, a zoom lens having a high variable power ratio (for example, having a large magnification not smaller than 5 and an angle of view not greater than 2 degrees (that is, having a focal length not shorter than 330 mm when converted to the corresponding one of a ⅔ type CCD) and a high optical performance is desired. Also, in such a pickup activity, since a camera is often used while being shouldered, a more compact and lighter-weight zoom lens easy to be taken anywhere is desired.

With respect to a zoom lens having the four unit structure, the following expressions are satisfied:

Expressions 1

fw=f 1 ×β 2 w ×β 3 w ×β 4   (a-1)

fT=f 1 ×β 2 T ×β 3 T ×β 4   (a-2)

Z=fT/fw =β 2 T /β 2 w ×β3 T /β 3 w   (a-3)

Wherein, fw and fT respectively represent the focal lengths of the overall system of the zoom lens at its wide angle and telephoto ends, f 1 represents the focal length of the first lens unit, Z represents the variable ratio of the zoom lens, βiw and βiT respectively represent the image-forming magnifications of an i-th lens unit at its wide angle and telephoto ends, and β 4 represents the image-forming magnification of the fourth lens unit, which is constant during power-varying since the fourth lens unit is fixed during the power-varying.

In order to achieve a telescopic feature, it is sufficient to make larger the focal length f 1 of the first lens unit or the image-forming magnifications β 2 T, β 3 T, and β 4 of the second, third, and fourth lens units at the telephoto end according to the expression (a-2).

However, when β 2 T, β 3 T, and β 4 are made greater, spherical and longitudinal chromatic aberrations generated in the first lens unit increase in proportion to the square of each image-forming magnification. Hence, it is better to make the focal length f 1 of the first lens unit larger, especially from the viewpoint of an optical performance at the telephoto end. Meanwhile, the expressions (a-1) to (a-3) can also be applied to a zoom lens having the three unit structure except for β 4 .

FIG. 18 is a conceptual view of a zoom lens having the four unit structure, illustrating a first lens unit L 1 fixed during power-varying and having a positive refractive power and a second lens unit L 2 moving toward an image plane upon the power-varying. In the figure, a reference character N represents the image point of the first lens unit L 1 , that is, the apparent object point of the second lens unit L 2 ; f 1 and f 2 respectively represent the focal lengths of the first and second lens units L 1 and L 2 ; reference characters e 1 w and e 1 T respectively represent principal-point intervals between the first and second lens units L 1 and L 2 at the wide angle and telephoto ends of the zoom lens; and a reference character mv represents a moving amount of the second lens unit L 2 from the wide angle to telephoto ends of the zoom lens.

In order to achieve a larger magnification, it is needed to make the ratio of the image-forming magnifications of the second and third lens units at the wide angle and telephoto ends of the zoom lens greater according to the expression (a-3). In particular, when attention is focused on a change of the image-forming magnifications β 2 of the second lens unit L 2 largely affecting the variable ratio, the following expressions are brought about:

According to the expression (b-3), the conditions for achieving a larger magnification are given as below,

(1) The focal lengths f 1 and f 2 of the first and second lens units L 1 and L 2 are small; (2) the moving amount mv of the second lens L 2 is large; (3) the principal-point interval e 1 w between the first and second lens units L 1 and L 2 at the wide angle end is large.

Unfortunately, making smaller the focal length f 1 of the first lens unit L 1 requires the image-forming magnifications of the second and following lens units to be larger, thereby increasing spherical and longitudinal chromatic aberrations and deteriorating the optical performance. Also, making smaller the focal length f 2 of second lens unit L 2 increases fluctuation of various aberrations in accordance with the power-varying, thereby deteriorating optical performance.

In addition, making larger the moving amount mv of the second lens unit L 2 requires a wider space for the second lens unit L 2 to move, thereby resulting in increase in the overall length of the zoom lens. Further, although making larger the principal-point interval e 1 w between the first and second lens units L 1 and L 2 is advantageous for a greater magnification, a large space is generated at the wide angle end between the first and second lens units L 1 and L 2 , thereby resulting in increases in the overall length of the zoom lens and the diameter of a front cell lens unit of the zoom lens.

Accordingly, in order to achieve a compact and light-weight zoom lens having a large magnification and a high performance, it is important to set parameters including the foregoing f 1 , f 2 , mv, and e 1 w in appropriate ranges in accordance with the specifications of the lens. Also, since the principal-point interval e 1 w between the first and second lens units L 1 and L 2 largely affects achievement of a greater magnification, the overall length of the lens, and the diameter of the front cell lens unit, it is especially essential to appropriately set the principal point of the first lens unit L 1 .

In the zoom lens disclosed in U.S. Pat. No. 5,442,486, the focal length f 1 of the first lens unit L 1 is about 600 mm to 900 mm, the principal-point interval e 1 w between the first and second lens units L 1 and L 2 is about 450 to 700 mm, and the moving amount mv of the second lens unit L 2 is about 10 to 15 mm. Also, in the zoom lens disclosed in Japanese Patent Laid-Open No. 10-90599, the focal length f 1 of the first lens unit L 1 is about 235 mm, the principal-point interval e 1 w between the first and second lens units L 1 and L 2 is about 110 mm, and the moving amount mv of the second lens unit L 2 is about 45. Thus, in both zoom lenses, since mv is smaller than (f 1 −e 1 w ) according to the expression (b-3), the variable ratio of the zoom lens is as small as about 1.5 to 3, thereby failing to satisfy the requirement of a greater magnification.

In the zoom lens disclosed in EP1092999, although the variable ratio of the zoom lens is not smaller than 40, the moving amount mv of the second lens unit L 2 is as large as about 100 to 120 mm, thereby resulting in a larger-sized zoom lens having the overall length of about 400 mm and the diameter of about 180 mm of the front cell lens unit.

The present invention is directed to a compact and light-weight zoom lens having a large magnification and a high optical performance, achieved by appropriately setting an optical arrangement of a first lens unit. The present invention is also directed to a pickup system incorporating the zoom lens.

In accordance with one aspect of the present invention, a zoom lens includes first, second, third and fourth lens units arranged in order from an object, respectively. The first lens unit is fixed during power-varying and has positive optical power. The second lens unit is movable during power-varying. The third lens unit is movable so as to compensate image-plane fluctuation in accordance with the power-varying. The fourth lens unit is fixed during the power-varying and has positive optical power. The first lens unit includes a first lens subunit having positive optical power and a second lens subunit having negative optical power, arranged in order from the object. One of the first and second subunits moves upon focus adjustment. Further, the following conditions are satisfied:

−2.5 <f 1 b/f 1 a <−0.6 and

0.2 <f 1 /fT <0.8.

Wherein f 1 , f 1 a , f 1 b , and fT respectively represent the focal lengths of the first lens unit, the first lens subunit, the second lens subunit, and the overall system of the zoom lens at its telephoto end.

Further features and advantages of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

FIG. 1 is a sectional view of a zoom lens according to a first embodiment (Numerical example 1) of the present invention at its wide angle end.

FIG. 2 illustrates aberration diagrams of the zoom lens serving as Numerical example 1 at its wide angle end.

FIG. 3 illustrates aberration diagrams of the zoom lens serving as Numerical example 1 at its focal length of 284.4 mm.

FIG. 4 illustrates aberration diagrams of the zoom lens serving as Numerical example 1 at its telephoto end.

FIG. 5 is a sectional view of a zoom lens according to a second embodiment (Numerical example 2) of the present invention at its wide angle end.

FIG. 6 illustrates aberration diagrams of the zoom lens serving as Numerical example 2 at its wide angle end.

FIG. 7 illustrates aberration diagrams of the zoom lens serving as Numerical example 2 at its focal length of 158.1 mm.

FIG. 8 illustrates aberration diagrams of the zoom lens serving as Numerical example 2 at its telephoto end.

FIG. 9 is a sectional view of a zoom lens according to a third embodiment (Numerical example 3) of the present invention at its wide angle end.

FIG. 10 illustrates aberration diagrams of the zoom lens serving as Numerical example 3 at its wide angle end.

FIG. 11 illustrates aberration diagrams of the zoom lens serving as Numerical example 3 at its focal length of 183.0 mm.

FIG. 12 illustrates aberration diagrams of the zoom lens serving as Numerical example 3 at its telephoto end.

FIG. 13 is a sectional view of a zoom lens according to a fourth embodiment (Numerical example 4) of the present invention at its wide angle end.

FIG. 14 illustrates aberration diagrams of the zoom lens serving as Numerical example 4 at its wide angle end.

FIG. 15 illustrates aberration diagrams of the zoom lens serving as Numerical example 4 at its focal length of 187.6 mm.

FIG. 16 illustrates aberration diagrams of the zoom lens serving as Numerical example 4 at its telephoto end.

FIG. 17 is a schematic view of the basic structure of a first lens unit of the zoom lens at its wide angle end, according to any one of the embodiments.

FIG. 18 is a schematic view of first and second lens units of a known zoom lens having a four unit structure.

FIG. 19 is a schematic view of a pickup system having the zoom lens according to any one of the embodiments incorporated therein.

Embodiments of the present invention will be described with reference to the attached drawings. Common elements of zoom lenses according to first to fourth embodiments (numerical examples 1 to 4) shown in FIGS. 1 , 5 , 9 , and 13 , which will be described later, will be first described. Each of the zoom lenses according to the first to fourth embodiments is a large-aperture, large-magnification, high-performance telephoto zoom lens, having an angle of view (2ω) not greater than 2.0 degrees, a variable power ratio of about 5 or greater, and an aperture ratio not greater than 3.0 at its wide angle end.

The zoom lens according to each embodiment includes, in order from an object (from the left side in the figure), a first lens unit L 1 fixed during power-varying and having a positive refractive power in terms of an optical power (the reciprocal of focal length), a second lens unit L 2 movable for power-varying, an aperture SP, a third lens unit L 3 movable for compensating fluctuation of an image plane in accordance with the power-varying, and a fourth lens unit L 4 fixed during the power-varying and having a positive refractive power.

The first lens unit L 1 includes a 1a-th lens subunit (a first lens subunit) L 1 a having a positive refractive power and a 1b-th lens subunit (a second lens subunit) L 1 b having a negative refractive power in order from the object. One of the 1a-th and 1b-th lens subunits L 1 a and L 1 b moves upon focus adjustment.

Thus, the zoom lens satisfies the following conditions:

−2.5 <f 1 b/f 1 a <−0.6  (1) and

0.2 <f 1 /fT <0.8  (2),

Wherein f 1 , f 1 a , f 1 b , and fT respectively represent the focal lengths of the first lens unit L 1 , the first lens subunit L 1 a , the second lens subunit L 1 b , and the overall system of the zoom lens at its telephoto end.

Further, the following conditions are also satisfied:

30<fT<Ld  (3) and

5<Z  (4),

Wherein Ld and Z respectively represent the diagonal length of an effective picture plane formed by the zoom lens and the zoom ratio of the zoom lens.

Furthermore, the following condition is additionally satisfied:

0.3<K<0.95  (5),

Wherein K represents the ratio of the distance from the first lens subunit to the rear focal position of the first lens unit to the focal length of the first lens unit.

When the first lens subunit L 1 a includes at least two positive lens elements and at least one negative lens element, the following condition is satisfied:

ν ap −ν an >30  (6),

Wherein ν ap and ν an respectively represent the averages of the Abbe constants of the positive and negative lens elements included in the first lens subunit.

When the 1b-th lens subunit L 1 b is made up by at least one positive lens element and at least one negative lens element, the following condition is satisfied:

ν bn −ν bp >5  (7),

Wherein ν bp and ν bn respectively represent the averages of the Abbe constants of the positive and negative lens elements included in the second lens subunit.

The conditional expressions (1) to (4) define the conditions for achieving reduction in size and weight, a larger magnification and a higher performance of the zoom lens. Referring now to FIG. 17 , the structure and the arrangement of the first lens unit L 1 of the zoom lens of each embodiment at its wide angle end will be described.

Reference characters L 1 to L 4 and L 1 a and L 1 b respectively represent those as described above. Meanwhile, the second lens unit L 2 , which will be described below, has a negative refractive power. A reference character N represents the image point of the first lens unit L 1 , that is, the apparent object point of the second lens unit L 2 . When the composite focal length of the 1a-th lens subunit L 1 a and the 1b-th lens subunit L 1 b (that is, the focal length of the first lens unit L 1 ) is represented by f 1 , the arrangement of the zoom lens shown in FIG. 17 is equivalent to the paraxial arrangement of the zoom lens shown in FIG. 18 .

As shown in FIG. 17 , by dividing the first lens unit L 1 into the 1a-th lens subunit L 1 a having a positive refractive power and the 1b-th lens subunit L 1 b having a negative refractive power so as to provide a so-called telephoto structure, the telephoto ratio of the first lens unit L 1 , that is, the ratio of the distance from the 1a-th lens subunit L 1 a to the rear focal point of the first lens unit L 1 to the focal length of the first lens unit L 1 can be reduced. With this structure, even when the principal-point interval e 1 w between the first and second lens units L 1 and L 2 is made wider so as to achieve a large magnification, useless dead space is reduced, thereby achieving both a large magnification and a reduction in size and weight of zoom lens at the same time.

When the focal lengths of the 1a-th and 1b-th lens subunits L 1 a and L 1 b are respectively represented by f 1 a and f 1 b ; the principal-point interval between the 1a-th and 1b-th lens subunits L 1 a and L 1 b is represented by e 1 ′; the image-forming magnification of the 1b-th lens subunit L 1 b is represented by β 1 b ; and the telephoto ratio of the first lens unit L 1 is represented by K, the following expressions are satisfied:

By appropriately setting the focal lengths f 1 a and f 1 b of the 1a-th and 1b-th lens subunits L 1 a and L 1 b so as to make the telephoto ratio K of the first lens unit L 1 smaller, the size and weight of the zoom lens can be reduced. Also, since the first lens unit L 1 is divided into the 1a-th and 1b-th lens subunits L 1 a and L 1 b , the degree of freedom of aberration compensation is increased, thereby achieving a higher performance of the zoom lens. In addition, since one of the 1a-th and 1b-th lens subunits L 1 a and L 1 b is moved for focus adjustment, the weight of a focus lens unit is reduced, thereby reducing the drive force of the zoom lens.

The conditional expression (1) defines the ratio of the focal length of the 1a-th lens subunit L 1 a to that of the 1b-th lens subunit L 1 b . When the ratio is smaller than the lower limit of the conditional expression (1), the telephoto ratio K of the first lens unit L 1 is great, and reduction in size of the zoom lens is hence not achieved; accordingly, lying out of the lower limit is undesirable.

When the ratio is greater than the upper limit of the conditional expression (1), the telephoto ratio K of the first lens unit L 1 is small and reduction in size of the zoom lens is therefore achieved. Whereas, when the telephoto ratio K is small, the focal lengths of the 1a-th and 1b-th lens subunits L 1 a and L 1 b are small according to the expressions (c-2) and (c-3). Hence, both subunit lenses have excessive refractive powers, thereby generating high-order aberrations and making them difficult to be compensated. Especially, a longitudinal chromatic aberration and high-order spherical aberrations on the telephoto side are great and difficult to be compensated by the other lens units. Also, since divergence of the zoom lens is excessively strong at the 1b-th lens subunit L 1 b , an off-axial light beam is incident on the 1a-th lens subunit L 1 a at a high position. Hence, the 1a-th lens subunit L 1 a is needed to have a large diameter in order to keep a necessary amount of ambient light.

When the zoom lens is focused by moving the 1a-th lens subunit L 1 a , since the 1a-th lens subunit L 1 a is delivered toward an object for focus adjustment within a limited distance, the 1a-th lens subunit L 1 a is needed to have a larger effective diameter, whereby this structure is undesirable.

Whereas, when the zoom lens is focused by moving the 1b-th lens subunit L 1 b , since the 1b-th lens subunit L 1 b has excessive refractive power, fluctuation of various aberrations, especially spherical and longitudinal chromatic aberrations at the telephoto end, in accordance with focus adjustment of the zoom lens, is great and difficult to be compensated even by the other lens units. Accordingly, this structure is undesirable.

When the lower and upper limits of the conditional expression (1) are respectively set at −2.0 and −0.7, more desirable advantages can be obtained.

The conditional expression (2) defines the focal length of the first lens unit L 1 with respect to that of the overall zoom lens system at the telephoto end. When the focal length of the first lens unit L 1 is made smaller than the lower limit of the conditional expression (2), a large magnification is advantageously achieved. Whereas, a telescopic feature is difficult to be achieved. Hence, in order to achieve a desirable focal length of the overall lens system at the telephoto end, the variable power ratio or the image-forming magnifications of the second and following lens units must be made greater, whereby the various aberrations are difficult to be appropriately compensated over the entire variable power range. Accordingly this structure is undesirable.

When the focal length of the first lens unit L 1 is greater than the upper limit of the conditional expression (2), a telescopic feature is easily obtained. However, the apparent object point of the second lens unit L 2 is moved away, and the moving amount of the second lens unit L 2 toward the image plane for achieving a large magnification is thus increased, resulting in the greater overall length of the zoom lens. Accordingly, lying out of the upper limit is undesirable.

When the lower and upper limits of the conditional expression (2) are respectively set at 0.25 and 0.7, more desirable advantages can be obtained.

The conditional expressions (3) and (4) define the specifications of the zoom lens to which the conditional expressions (1) and (2) are effectively applied. As described above, the zoom lens according to each of the embodiments has an angle of view (2×) not greater than 2.0 degrees at its telephoto end and a variable power ratio not smaller than 5. When the values of fT/Ld and Z of the zoom lens are smaller than the respective lower limits of the conditional expressions (3) and (4), even when the zoom lens has a reduced size and weight and also a high performance, the zoom lens cannot be called that it has a satisfactorily large magnification.

Both upper limits of the conditional expressions (3) and (4) can be set at about 200 from the viewpoint of their feasibilities.

The conditional expression (5) defines the ratio of the distance from the 1a-th lens subunit L 1 a to the rear focal point of the first lens unit L 1 to the focal length of the first lens unit L 1 (hereinafter, simply referred to as the telephoto ratio of the first lens unit L 1 ). When the telephoto ratio is greater than the upper limit of the conditional expression (5), reducing the size and weight of the zoom lens is difficult. Whereas, when the telephoto ratio is smaller than the lower limit, the 1a-th and 1b-th lens subunits L 1 a and L 1 b both have excessive optical power, and achieving the zoom lens so as to have a high performance is hence difficult. Accordingly, lying out of the upper and lower limits is undesirable.

The conditional expression (6) defines the condition for satisfactorily compensating the longitudinal chromatic aberration of the zoom lens at its telephoto end. Since the zoom lens according to each embodiment has a relatively large focal length, the zoom lens presents a problem of a longitudinal chromatic aberration on its telephoto side. When the size and weight of the zoom lens are reduced by making smaller the telephoto ratio of the first lens unit L 1 , the image-forming magnification β 1 b of the 1b-th lens subunit L 1 b becomes greater according to the foregoing expressions (c-1) to (c-3). Since the longitudinal chromatic aberration generating in the 1a-th lens subunit L 1 a is in proportion to the square of the image-forming magnification β 1 b of the 1b-th lens subunit L 1 b , the chromatic aberration in the 1a-th lens subunit L 1 a must be satisfactorily compensated.

Particularly, in the zoom lens having an angle of view smaller than 2.0 degrees at its telephoto end, the chromatic aberration of the zoom lens cannot be satisfactorily compensated when the 1a-th lens subunit L 1 a made up by a single piece of positive lens element and a single piece of negative lens element. To this end, by including at least two positive lens elements in the 1a-th lens subunit L 1 a and also by selecting a material having a small dispersion for the zoom lens, the longitudinal chromatic aberration at the telephoto end can be satisfactorily compensated.

Thus, in order to compensate the longitudinal chromatic aberration at the telephoto end, the conditional expression (6) defines the lower limit of a difference in the averages of the Abbe constants of the positive and negative lens elements included in the 1a-th lens subunit L 1 a . When the difference is smaller than the lower limit of the conditional expression (6), the longitudinal chromatic aberration generating in the 1a-th lens subunit L 1 a at the telephoto end is great and therefore difficult to be compensated by the other lens units. Accordingly lying out of the lower limit is undesirable. Also, not only other aberrations increase because of an increase in the number of lens elements and an increase in a curvature of each lens element included in the 1a-th lens subunit L 1 a for compensation of the chromatic aberration, but also the size of each lens element becomes greater for keeping its center thickness and edge thickness different. Accordingly lying out of the lower limit is undesirable. In addition, when the 1a-th lens subunit L 1 a is delivered toward an object upon focus adjustment, fluctuation of the longitudinal chromatic aberration in accordance with the focus adjustment is large. Accordingly lying out of the lower limit is undesirable.

The conditional expression (7) defines the condition for satisfactorily compensating the longitudinal chromatic aberration at the telephoto end and also serves as the condition for inhibiting fluctuation of the longitudinal chromatic aberration at the telephoto end in accordance with the focus adjustment when the 1b-th lens subunit L 1 b is moved for focus adjustment. More particularly, the conditional expression (7) defines the lower limit of a difference in the averages of the Abbe constants of the positive and negative lens elements included in the 1b-th lens subunit L 1 b . When the difference is smaller than the lower limit of the conditional expression (7), the longitudinal chromatic aberration generated in the 1b-th lens subunit L 1 b is especially great and difficult to be compensated by the other lens units. Accordingly lying out of the lower limit is undesirable. Also, not only other aberrations increase because of an increase in the number of lens elements and an increase in a curvature of each lens element included in the 1b-th lens subunit L 1 b for compensation of the chromatic aberration, but also the size of each lens element becomes greater for keeping its center thickness and edge thickness different. Accordingly lying out of the lower limit is undesirable. In addition, when a group of the 1b-th lens subunit L 1 b is delivered toward an object upon focus adjustment, fluctuation of the longitudinal chromatic aberration in accordance with the focus adjustment is large. Accordingly lying out of the lower limit is undesirable.

In the zoom lens according to each embodiment, a focal-length-transforming optical system (extender) EX may be disposed so as to be inserted into or taken out from a space S formed in the fourth lens unit L 4 as shown in FIG. 1 .

First Embodiment

FIG. 1 is a sectional view of a zoom lens according to a first embodiment (Numerical example 1) of the present invention at its wide angle end, while focusing at an infinite distance. FIGS. 2 to 4 illustrate aberration diagrams of the zoom lens used for Numerical example 1 at its wide angle end, middle position f=284.4 mm, and telephoto end, respectively. In each aberration diagram, notations e and g respectively represent aberrations of an e and g lines, and reference characters S and M respectively represent aberrations of sagittal and meridional image surfaces (the same is applied to the aberration diagrams of the other numerical examples).

In FIG. 1 , the first lens unit L 1 having a positive refractive power serves as a focus lens unit (a front cell lens unit). The second lens unit L 2 having a negative refractive power for power-varying serves as a variator lens unit and performs the power-varying from its wide angle end (Wide) to telephoto end (Tele) by monotonously moving along the optical axis toward an image plane. The third lens unit L 3 having a negative refractive power serves as a compensator lens unit and moves nonlinearly along the optical axis so as to draw a locus projecting towards the object in order to compensate fluctuation of an image plane in accordance with the power-varying. The variator lens unit L 2 and the compensator lens unit L 3 make up a power-varying system.

The fourth lens unit L 4 having a positive refractive power serves as a fixed relay lens unit. The aperture SP is disposed between the compensator lens unit L 3 and the relay lens unit L 4 , that is, between the third and fourth lens units L 3 and L 4 . A glass block B indicates a color separation prism, an optical filter, or the like.

The focus lens unit L 1 includes a positive sub-system (that is, the 1a-th lens subunit L 1 a ) and a negative sub-system (that is, the 1b-th lens subunit) L 1 b in order from the object, and the positive sub-system L 1 a includes three pieces of positive lens elements and a single piece of negative lens element. The negative sub-system L 1 b is formed by bonding single pieces of positive and negative lens elements to each other.

In the zoom lens according to the present embodiment, the focal length at its telephoto end is about 402 mm; the moving amount of the variator lens unit L 2 between its wide angle and telephoto ends is about 76.56 mm, and the variable power ratio is about 13.4, thereby achieving super-telescopic and high-magnification features. Since the parameters f 1 b /f 1 a and f 1 /fT of the zoom lens according to the present embodiment, appearing in the conditional expressions (1) and (2) respectively have the following values, the respective conditions are satisfied, thereby achieving reduction in size and weight of the zoom lens:

f 1 b/f 1 a =−1.7, and  (1)

f 1 /fT =0.44.  (2)

Since the parameters (ν ap −ν an ) and (ν bn −ν bp ) of the zoom lens, appearing in the conditional expressions (6) and (7) respectively have the following values, the respective conditions are satisfied, thereby satisfactorily compensating the longitudinal chromatic aberration at the telephoto end:

ν ap −ν an =49. 31, and  (6)

ν bn −ν bp =5.79.  (7)

In the present embodiment, the positive sub-system L 1 a is fixed upon focus adjustment, and the negative sub-system L 1 b moves along the optical axis upon the focus adjustment. In other words, the zoom lens according to the present embodiment is of a so-called inner focus type. Meanwhile, the positive sub-system L 1 a can alternatively perform the focal adjustment.

Although the compensator lens unit L 3 compensating image-plane fluctuation has a negative refractive power in the present embodiment, it may have a positive refractive power.

Table 1 shows structural data of the zoom lens according to the present embodiment (Numerical example 1). In the table, notations f, Fno, and ω respectively represent the focal length of the overall system of the zoom lens, an F-number, and half an angle of view (denoted by w in the table). Also, notations ri and di respectively represent a curvature of radius of the surface of the i-th lens element from the object and the gap (including an air gap) between the surfaces of the i-th and the (i+1)-th lens elements. In addition, notations ni and νi (denoted by vi in the table) respectively represent a refractive index and an Abbe constant of a material forming the i-th lens element. A numerical value 0.000 of ri indicates an infinitive number. The meanings of these notations are applied in the same fashion as in each of Numerical examples (shown in Table 2 to 4), which will be described later.

Second Embodiment

FIG. 5 is a sectional view of a zoom lens according to a second embodiment (Numerical example 2) of the present invention at its wide angle end, while focusing at an infinite distance. FIGS. 6 to 8 illustrate aberration diagrams of the zoom lens used for Numerical example 2 at its wide angle end, middle position f=158.1 mm, and telephoto end, respectively.

In FIG. 5 , the first lens unit L 1 having a positive refractive power serves as a focus lens unit (a front cell lens unit). The second lens unit L 2 having a negative refractive power for power-varying serves as a variator lens unit and performs the power-varying from its wide angle end (Wide) to telephoto end (Tele) by monotonously moving along the optical axis toward an image plane. The third lens unit L 3 having a negative refractive power serves as a compensator lens unit and moves nonlinearly along the optical axis so as to draw a locus projecting towards the object in order to compensate fluctuation of the image plane in accordance with the power-varying. The variator lens unit L 2 and the compensator lens unit L 3 make up a power-varying system.

The fourth lens unit L 4 having a positive refractive power serves as a fixed relay lens unit. The aperture SP is disposed between the third and fourth lens units. A glass block B indicates a color separation prism, an optical filter, or the like.

The focus lens unit L 1 includes a positive sub-system (that is, the 1a-th lens subunit L 1 a ) and a negative sub-system (that is, the 1b-th lens subunit) L 1 b in order from an object, and the positive sub-system L 1 a includes four pieces of positive lens elements and a single piece of negative lens element. The negative sub-system L 1 b is formed by bonding single pieces of positive and negative lens elements to each other.

In the zoom lens according to the present embodiment, the focal length at its telephoto end is about 500 mm, the moving amount of the variator lens unit L 2 between its wide angle and telephoto ends is about 60.32 mm, and the variable power ratio is about 10, thereby achieving super-telescopic and high-magnification features.

Since the parameters f 1 b /f 1 a and f 1 /fT of the zoom lens according to the present embodiment, appearing in the conditional expressions (1) and (2) respectively have the following values, the respective conditions are satisfied, thereby achieving reduction in size and weight of the zoom lens:

f 1 b/f 1 a =−0.794, and  (1)

f 1 /fT =0.48.  (2)

Since the parameters (ν ap −ν an ) and (ν bn −ν bp ) of the zoom lens, appearing in the conditional expressions (6) and (7) respectively have the following values, the respective conditions are satisfied, thereby satisfactorily compensating the longitudinal chromatic aberration at the telephoto end:

ν a −ν an =52.58, and  (6)

ν bn −ν bp =18.78.  (7)

In the present embodiment, the positive sub-system L 1 a is fixed upon focus adjustment, and the negative sub-system L 1 b moves along the optical axis upon the focus adjustment. In other words, the zoom lens according to the present embodiment is of a so-called inner focus type. Alternatively, the focus adjustment can be performed by moving the positive sub-system L 1 a.

Although the compensator lens unit L 3 compensating fluctuation of an image plane has a negative refractive power in the present embodiment, it may have a positive refractive power.

Table 2 shows structural data of the zoom lens according to the present embodiment (Numerical example 2).

Third Embodiment

FIG. 9 is a sectional view of a zoom lens according to a third embodiment (Numerical example 3) of the present invention at its wide angle end, while focusing at an infinite distance. FIGS. 10 to 12 illustrate aberration diagrams of the zoom lens used for Numerical example 3 at its wide angle end, middle position f=183.0 mm, and telephoto end, respectively.

In FIG. 9 , the first lens unit L 1 having a positive refractive power serves as a focus lens unit (a front cell lens unit). The second lens unit L 2 having a negative refractive power for power-varying serves as a variator lens unit and performs the power-varying from its wide angle end (Wide) to telephoto end (Tele) by monotonously moving along the optical axis toward an image plane. The third lens unit L 3 having a negative refractive power serves as a compensator lens unit and moves nonlinearly along the optical axis so as to draw a locus projecting towards the object in order to compensate fluctuation of the image plane in accordance with the power-varying. The variator lens unit L 2 and the compensator lens unit L 3 make up a power-varying system.

The fourth lens unit L 4 having a positive refractive power serves as a fixed relay lens unit. The aperture SP is disposed between the third and fourth lens units. A glass block B indicates a color separation prism, an optical filter, or the like.

The focus lens unit L 1 includes a positive sub-system (that is, the 1a-th lens subunit L 1 a ) and a negative sub-system (that is, the 1b-th lens subunit) L 1 b in order from an object, and the positive sub-system L 1 a includes four pieces of positive lens elements and a single piece of negative lens element. The negative sub-system L 1 b is formed by bonding single pieces of positive and negative lens elements to each other.

In the zoom lens according to the present embodiment, the focal length at its telephoto end is about 670 mm, the moving amount of the variator lens unit L 2 between its wide angle and telephoto ends is about 71.52 mm, and the variable power ratio is about 13.4, thereby achieving super-telescopic and high-magnification features.

Since the parameters f 1 b /f 1 a and f 1 /fT of the zoom lens according to the present embodiment, appearing in the conditional expressions (1) and (2) respectively have the following values, the respective conditions are satisfied, thereby achieving reduction in size and weight of the zoom lens:

f 1 b/f 1 a =−0.794, and  (1)

f 1 /fT =0.300.  (2)

Since the parameters (ν ap −ν an ) and (ν bn −ν bp ) of the zoom lens, appearing in the conditional expressions (6) and (7) respectively have the following values, the respective conditions are satisfied, thereby satisfactorily compensating the longitudinal chromatic aberration at the telephoto end:

ν ap −ν an =56.44, and  (6)

ν bn −ν bp =24.18.  (7)

In the present embodiment, the positive sub-system L 1 a is fixed upon focus adjustment, and the negative sub-system L 1 b moves along the optical axis upon the focus adjustment. In other words, the zoom lens according to the present embodiment is of a so-called inner focus type. Alternatively, the focus adjustment can be performed by moving the positive sub-system L 1 a.

Although the compensator lens unit L 3 compensating fluctuation of an image plane has a negative refractive power in the present embodiment, it may have a positive refractive power.

Table 3 shows structural data of the zoom lens according to the present embodiment (Numerical example 3).

Fourth Embodiment

FIG. 13 is a sectional view of a zoom lens according to a fourth embodiment (Numerical example 4) of the present invention at its wide angle end, while focusing at an infinite distance. FIGS. 14 to 16 illustrate aberration diagrams of the zoom lens used for Numerical example 4 at its wide angle end, middle position f=187.6 mm, and telephoto end, respectively.

In FIG. 13 , the first lens unit L 1 shown in FIG. 13 having a positive refractive power serves as a focus lens unit (a front cell lens unit). The second lens unit L 2 having a negative refractive power for power-varying serves as a variator lens unit and performs the power-varying from its wide angle end (Wide) to telephoto end (Tele) by monotonously moving along the optical axis toward an image plane. The third lens unit L 3 having a negative refractive power serves as a compensator lens unit and moves nonlinearly along the optical axis so as to draw a locus projecting towards the object in order to compensate fluctuation of the image plane in accordance with the power-varying. The variator lens unit L 2 and the compensator lens unit L 3 make up a power-varying system.

The fourth lens unit L 4 having a positive refractive power serves as a fixed relay lens unit. The aperture SP is disposed between the third and fourth lens units. A glass block B indicates a color separation prism, an optical filter, or the like.

The focus lens unit L 1 includes a positive sub-system (that is, the 1a-th lens subunit) L 1 a and a negative sub-system (that is, the 1b-th lens subunit) L 1 b in order from an object. The positive sub-system L 1 a includes three pieces of positive lens elements and a single piece of negative lens element. The negative sub-system L 1 b is formed by bonding single pieces of positive and negative lens elements to each other.

In the zoom lens according to the present embodiment, the focal length at its telephoto end is about 440 mm, the moving amount of the variator lens unit L 2 between its wide angle and telephoto ends is about 56.08 mm, and the variable power ratio is about 5.5, thereby achieving super-telescopic and high-magnification features.

Since the parameters f 1 b /f 1 a and f 1 /fT of the zoom lens according to the present embodiment, appearing in the conditional expressions (1) and (2) respectively have the following values, the respective conditions are satisfied, thereby achieving reduction in size and weight of the zoom lens:

f 1 b/f 1 a =−0.715, and  (1)

f 1 /fT =0.57.  (2)

Since the parameters (ν ap −ν an ) and (ν bn −ν bp ) of the zoom lens, appearing in the conditional expressions (6) and (7) respectively have the following values, the respective conditions are satisfied, thereby satisfactorily compensating the longitudinal chromatic aberration at the telephoto end:

ν ap −ν an =48.81, and  (6)

ν bn −ν bp =18.78.  (7)

In the present embodiment, the positive sub-system L 1 a is fixed upon focus adjustment, and the negative sub-system L 1 b moves along the optical axis upon the focus adjustment. That is, the zoom lens according to the present embodiment is of a so-called inner focus type. Alternatively, the focus adjustment can be performed by moving the positive sub-system L 1 a.

Although the compensator lens unit L 3 compensating fluctuation of an image plane has a negative refractive power in the present embodiment, it may have a positive refractive power.

Table 4 shows structural data of the zoom lens according to the present embodiment (Numerical example 4).

In the present embodiment, the zoom lens is of a so-called inner focus type in which the positive sub-system L 1 a is fixed upon focus adjustment, and the negative sub-system L 1 b moves along the optical axis upon the focus adjustment. Alternatively, the focus adjustment can be performed by moving the positive sub-system L 1 a . Although the compensator lens unit L 3 compensating fluctuation of an image surface has a negative refractive power in the present embodiment, it may have a positive refractive power.

Table 5 shows values of the parameters appearing in the conditional expressions (1) to (7) for the respective Numerical examples 1 to 4.

Table 6 shows values of parameters appearing in the foregoing expression (a-1) to (c-3) for the respective Numerical examples 1 to 4.

The zoom lens according to any one of the embodiments is replaceably mounted in a pickup apparatus such as a TV camera or a video camera.

Referring now to FIG. 19 , a pickup system (a TV camera system) in which the zoom lens according to any one of the embodiments is incorporated as a pickup optical system will be described.

As shown in FIG. 19 , a pickup system 117 includes a zoom lens 101 (that is, the zoom lens according to any one of the embodiments) and a camera 111 serving as a pickup apparatus and is formed by mounting the zoom lens 101 in the camera 111 .

The zoom lens 101 includes a front cell lens unit (a first lens unit) 102 moving along the optical axis by a manual operation so as to serve as a focus lens unit, a variator lens unit (a second lens unit) 103 a moving along the optical axis for power-varying, a compensator lens unit (a third lens unit) 103 b moving along the optical axis for compensating image-plane fluctuation in accordance with the power-varying, an aperture 104 , and a fixed relay lens unit (a fourth lens unit) 105 .

The pickup system 117 also includes a zoom-mechanism member 109 such as a cam, mechanically controlling the positions, along the optical axis, of the lens units 103 a and 103 b moving upon power-varying, and allowing the zoom lens to be manually operated.

The camera 111 includes a glass block 106 corresponding to an optical filter or a color separation prism, an image-pickup element (a photoelectric conversion element) 107 such as a CCD sensor or a CMOS sensor, receiving an object image formed by the zoom lens 101 , and a camera controller 108 including a CPU, for controlling the camera 111 .

The pickup system 117 further includes a drive unit 116 placed on the side surface of the zoom lens 101 . The drive unit 116 has a variety of operational switches including a zoom switch and an aperture selector switch disposed therein and serves as an interface between the zoom lens 101 and a camera operator. The drive unit 116 includes a zoom actuator 112 driving the zoom-mechanism member 109 such that the lens units 103 a and 103 b are moved so as to perform power-varying, an aperture actuator 113 driving the aperture 104 , and a drive unit controller 115 including a CPU, for controlling the drive unit 116 .

Although the zoom lens shown in FIG. 19 is of a type in which the drive unit is externally placed, the present invention is applicable to another type of zoom lens having the function of the drive unit built therein. Also, the zoom lens may have an autofocus function mounted therein, detecting its focal point and controlling the position of the focus lens unit 102 .

Although a refractive power of the lens unit or the lens element is described in the foregoing embodiments, the present invention is applicable to a case in which the lens unit or the lens element has an optical power equivalent to that in accordance with refraction of a diffractive optics, for example, bonded to a lens surface.

According to the present invention, by appropriately setting the optical power arrangement of the first and second lens subunits of the first lens unit, a compact and light-weight zoom lens having a high optical performance can be achieved even when a large magnification is provided.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims priority from Japanese Patent Application No. 2004-108589 filed Mar. 31, 2004, which is hereby incorporated by reference herein.