JPH01193709A - Large variable power rate zoom lens system including wide angle range - Google Patents

Abstract

PURPOSE:To excellently compensate various aberrations by varying the focal length of the whole system while holding an image plane position constant by moving 1st, 2nd, and 4th lens groups in the direction of the optical axis. CONSTITUTION:This system is so constituted that when the lens groups move from the short-focus side (a) to the long-focus side (b), l1>l1', l2<l2', and l3>l3', where l1 and l1' are the air gap between the 1st lens group L1 and the 2nd lens group L2, l2 and l2' are the air gap between the 2nd lens group L2 and a 3rd lens group L3, and l3 and l3' are the air gap between the 3rd lens group L3 and the 4th lens group L4. The l1>l1' is a condition for constituting a reverse telephoto type on the short-focus side (a) and l2<l2' is a condition for constituting a telephoto type on the long-focus side (b). For the telephoto type on the long-focus side (b), when the lens system is divided roughly into the front group consisting of the 1st and 2nd lens group and the rear group consisting of the 3rd and 4th lens groups, the front group has positive refracting power and the rear group has negative refracting power. Consequently, the aberrations are compensated excellently over the entire focal length range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens system, and an object of the present invention is to provide a zoom lens system with a wide angle of view of 76° on the short focus side, and
The object of the present invention is to provide a compact zoom lens system with a zoom ratio of about 2.5 to 3.5 times, good aberrations, and a small size.

The present invention will be explained below. On the short focus side, the zoom lens according to the present invention is an inverse lens that is roughly divided into two groups: a first lens group having a negative refractive power, and a second, third, and fourth lens group having a positive composite refractive power. The first lens has a telephoto configuration and has a positive composite refractive power on the long focal point side. a second lens group, and a third lens group having a negative composite refractive power. It has a telephoto configuration consisting of two main groups called the fourth lens group, and therefore the length of the entire system on the long focal point side is shorter than a conventional two-component wide-angle zoom lens. In the present invention, the above-mentioned configuration is applied at least to the first. Second. This feature is realized by moving the fourth lens group.

Further, as a feature of the zoom lens system of the present invention, the second lens group has a configuration having a biconvex lens with negative meniscus lenses cemented on both sides and a positive single lens, which can effectively correct various aberrations. I'm planning on doing it.

That is, the zoom lens system of the present invention has, in order from the object side:
The first lens group has a negative composite refractive power as a whole, the second lens group has a biconvex lens with negative meniscus lenses cemented on both sides and a positive single lens and has a positive composite refractive power as a whole, and the second lens group has a negative composite refractive power as a whole. The air gap between the first lens group and the second lens group on the short focus side is composed of a third lens group having a composite refractive power of and the third lens group and the 4121st
At least the first ．． 2nd and 4th
It is characterized by changing the focal length of the entire system while keeping the image plane position constant by moving the lens group in the optical axis direction.

To explain in more detail the movement method of the zoom lens system of the present invention with reference to FIG. 1, the air gap between the first lens group and the second lens group when changing from the short focus side (axis) to the long focus side (b). 11 and Ll, the air distances 2□ and 2□゛ between the second and third lens groups, and the air distances 13 and 23'' between the third and fourth lens groups, respectively. The configuration is such that the relationships fl >11Z1, <i,'', and ls >lz' are satisfied. ffi, M! ,'
is a requirement for configuring an inverted telephoto type on the short focal length side (a), and i2 is a requirement for configuring a telephoto type on the long focal length side (b).

The relationship of refractive power for a telephoto type on the long focal length side (b) is that the lens system is divided into a front group consisting of the 1st lens group, the 3rd lens group, and the 3rd lens group. Fourth
When the lens group is roughly divided into rear groups, the front group has positive refractive power and the rear group has negative refractive power. This is the first thing
．． Second. Third. The focal length of the fourth lens group is f
+, f z, f 3. When expressed as f a, f2×1f+l, 1fil<fs. In the present invention, by adopting the above configuration, a compact high zoom ratio zoom lens is realized.

In addition, in the four-group zoom lens system of the present invention, the second lens group has a biconvex lens with negative meniscus lenses cemented on both sides and a positive single lens, so that aberration correction within the second lens group is possible. In addition, the spherical aberration and chromatic aberration of the zoom lens system as a whole are well corrected over the entire focal length range.

Note that, unlike the configuration of the second lens group of the present invention, the second lens group has a total of three lenses including a two-piece cemented lens and another single lens.
If the second lens group is composed of a plurality of lenses, the aberration correction of the second lens group itself becomes somewhat incomplete, and the air gap between the second lens group and the third lens group must be used for aberration correction. Although this configuration is advantageous in reducing the number of lenses, on the other hand, since the error in the air spacing greatly affects the image performance, the cam accuracy becomes strict due to the lens barrel configuration, which is not preferable in terms of manufacturing.

Furthermore, compared to the case where two two-piece cemented lenses are used in the second lens group, according to the second lens group configuration of the present invention, the composite core thickness can be made considerably smaller, which is also advantageous for the amount of peripheral light. .

Further, in a preferred embodiment of the second lens group, it is desirable that the negative meniscus lenses bonded to both surfaces of the biconvex lens have different refractive indexes and Abbe numbers.

In the present invention, by further satisfying the following conditions,
Better aberration correction becomes possible.

1 f , I (2) 0.5<<1.3If, 1 (3) 0.9< f Z/ f , 1<1.5 (4)
0.8<l f31/f,<1.6However,
R is the radius of curvature of the object-side surface that forms the first air interval from the object side.

fw is the focal length of the entire system on the short focus side.

f is the focal length of the entire system on the long focal length side.

Condition (1) defines the focal length of the lens group,
This is to balance lens performance over the entire focal length range. As the lower limit value is exceeded, it becomes difficult to correct spherical aberration and astigmatism on the long focus side, and as the upper limit value is exceeded, the overall length on the short focus side and the long focus side becomes longer, which defeats the purpose of compactness.

Condition (2) defines the radius of curvature of the object-side surface that forms the first air gap from the object side, that is, the image-side surface of the first lens from the object side. A large amount of coma aberration occurs from the intermediate focal point region to the long focal point side and is difficult to correct. On the other hand, as the upper limit is exceeded, it becomes difficult to balance spherical aberration, and if forced correction is performed, coma and distortion will worsen.

Furthermore, when implementing the four-group zoom lens system of the present invention, it is also possible to fix the third lens group with respect to the image plane. By fixing the third lens group on the optical axis during zooming in this way, the number of zoom cams can be reduced, which is advantageous in terms of the lens barrel construction. By providing this fixed group with an aperture, it is even more advantageous in terms of the lens barrel construction.

Conditions (3) and (4) are both intended to ensure that various aberrations can be well corrected over the entire focal length range without moving the third lens group. As the lower limit of condition (3) is exceeded, the refractive power of the second lens group becomes stronger, which is advantageous for downsizing the lens system, but it becomes difficult to correct spherical aberration and astigmatism, making it difficult to use the third lens group. You will have no choice but to move and correct it.

On the other hand, as the upper limit is exceeded, the refractive power of the second lens group becomes weaker, which is advantageous in correcting aberrations, but the lens system becomes larger in both overall length and diameter, which goes against the purpose of miniaturization of the present invention. Also,
As the lower limit of condition (4) is exceeded, the refractive power of the third lens group becomes stronger, and it becomes difficult to correct distortion and coma aberration over the entire focal length range. On the other hand, as the upper limit is exceeded, the refractive power of the third lens group becomes weaker, and as already mentioned, f
, < l rtl, 1 F31 < [4 The refractive power of the fourth lens group also becomes weak. For this reason, it becomes difficult to configure a telephoto type lens on the long focal length side, and the lens system becomes larger.

Furthermore, if the first lens group is configured with a concave lens in advance,
The effective diameter of the front lens, which is a problem with high-magnification zoom lenses, can be made significantly smaller than that of previous convex lens types, making it possible to make the lens system more compact.

Examples of the present invention are shown below. In Examples 1 to 5, the second lens group and the fourth lens group move in the same way, and in Example 6, all the moving lens groups move differently. Second thing. 4. 6. 8.10.12 (S) in the figure indicates the aperture position.

Example 1 f = 28.8 ~ 50.0 ~ 82.5 FN, , = 3
．． 6-4.0-4.63 Radius of curvature Axis spacing Refractive index (Nd) Dispersion (νd) rs 374.702 f, = -41,667, rz = 3o, ss3° f 3 =
-39,370,f,=56.840fz/fw=
1.07. l fjl/fw=1.37 Example 2 f=28.8~50.0~82.5 FNo. 3
．． 6-4.0-4.63 Radius of curvature Axial spacing Refractive index (Nd) Dispersion (νd) d+< 3.70-9.3
3~16.73dza 1.20 Nls 1.
805 ν+s 41.0rzs 118.6
97 f,=-45,455,f! =28.902°fs--
27,051,f,=44.352f2/fw-
−1,00,l f s l / f , 1=0.9
4 Example 3 f=28.8-50.0-82.5 FN, ,=3.
6-4.0-4.63 Radius of curvature Axis top surface interval Refractive index (
Nd) Dispersion (νd)f, = 41.667,
f z = 31.034° f3--38.478.
f,=59.847f z/ r w=1.08. l
r s l / r w = 1.35 If, 1 = 0.855 f completed; T] 1 Example 4 f = 28.8 - 50.0 - 82.5 FN, , = 3.
6-4.0-4.6 Radius of curvature Axial surface spacing Refractive index (N
d) Dispersion (νd) r+3 jυ, 1jl f, = -41,667, ft = 30.660° f3 me 39.606. f, = 58.908f t/f
w=1.07. l f 31 / r , 1=1.3
8 Example 5 f = 28.8 ~ 50.0 ~ 82.5 FNO, = 3
．． 6-4.0-4.6 radius of curvature axial spacing refractive index (
Nd) Dispersion (νd)r! 34.144 f, = -33,333, ft = 28.604° f3 = -
36,785,f,=53.285rz/fw=
0.99. l f s l / f w-1, 28 Example 6 f = 28.8-55.0-102. OFNO,=3.
6-4.0-4.6 Radius of curvature Axial surface spacing Refractive index (N
d) Dispersion (νd) d+s J, 4tl~11j
,Z6~4U,44f,=-40,000,fz"'3
6゜131゜f, = -30,661,f, = 38.38
9fz/fw=1.26. l f31/f,=1.
06

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a basic schematic configuration of a zoom lens system according to the present invention, in which (a) shows a state on the short focus side and (b) shows a state on the long focus side. FIGS. 2, 4, 6, 8, 10, and 12 show lens configuration diagrams of Examples 1 to 6 of the zoom lens system according to the present invention, and FIGS. 5, 7, 9, 11, and 13 are Examples 1 to 6, respectively.
The aberration diagram shows spherical aberration and astigmatism at each end and middle focal length, respectively. It is shown as distortion aberration. Ll-Group 1121. Lg"' - 2nd lens group. L3 - - 3rd lens group. L4 - 4th lens group. Fig. 1 Fig. 2 L!
Solstice Day 4-Fig.

Claims (2)

[Claims] (1) In order from the object side, the first lens group has a negative composite refractive power as a whole, a biconvex lens with negative meniscus lenses cemented on both sides, and a positive single lens, and has a positive composite refractive power as a whole. It is composed of a second lens group, a third lens group having a negative composite refractive power as a whole, and a fourth lens group having a positive composite refractive power as a whole. The air distance between the lens groups and the air distance between the third lens group and the fourth lens group decreases on the long focus side, and the distance between the second lens group and the third lens group on the short focus side decreases. The focal length of the entire system is changed while keeping the image plane position constant by moving at least the first, second, and fourth lens groups in the optical axis direction so that the air gap between them increases on the long focal point side. A high variable magnification zoom lens system that includes a wide-angle range. (2) A zoom lens system according to claim 1, which satisfies the following conditions: 0.5<|f_1
|/√(f_W・f_T)<1.2 However, f_1 is the first
The focal length of the lens group, f_W is the focal length of the entire system on the short focal length side, and f_T is the focal length of the entire system on the long focal length side.