JPS6032016A - Zoom lens having near distance aberration correcting function - Google Patents

Abstract

PURPOSE:To reduce the variation of bending of an image surface at the focusing time and to obtain a zoom lens having wide angle zooming of 70 deg. or more view angle at its wide end, F/2.8 brightness and a comparatively simple constitution by changing a proper air interval in a back group converging system. CONSTITUTION:The air interval between the front group diverging system I and the rear group converging system II by moving both the systems I , II as shown by the arrow to perform zooming. At the focusing time, the front group diverging system I is delivered to the front as shown by the arrow and a front group IIa out of the rear group converging system II is interlocked with the delivery of the system I and moved to the back to perform focusing from the infinite point to a near distance. The air interval d15 between the IIa and IIb at the focusing of an object point having 1m distance is 1.42.

Description

Detailed Description of the Invention The present invention is a two-group zoom lens that performs focusing by extending the front group, and has a short-distance aberration correction mechanism that corrects distortion of aberrations when focusing on a short-distance object. It is related to.

In recent years, the development of zoom lenses in the field of photographic lenses has been remarkable. The main direction of development is the direction of increasing the zoom ratio, but another direction of development is the direction of increasing the brightness. In particular, it is desired to reduce the brightness of a zoom lens with an angle of view of 70 degrees or more at the wide end, which is called a wide zoom lens, but it is quite difficult to achieve this.

Conventionally called wide zoom, 25-50m+n, 28-
The lens system for the 50 marriage class is 73.5 even if it is V4 or bright.
It was about. In addition, recently, a camera with a /2.8 class at the wide end has been known, but at the tele end it is /3.5, which is inconvenient for the user when determining exposure.

Furthermore, in a two-group zoom system consisting of a front group divergence system and a rear group convergent system, focusing is generally performed by extending the front group divergence system. However, since it is a wide-angle lens, the change in field curvature is large when the object point moves from infinity to a short distance, so with a lens of about /44, the field curvature is tolerable because it is within the depth of focus. Even with '/2.8 class lenses, the axial and external performance deteriorates significantly. This was the biggest obstacle in the development of a bright wide zoom lens.

Conventionally, in a two-group zoom, in order to correct the field curvature that occurs when the front group divergence system is extended for focusing, an air gap is provided in the front group that is variable in conjunction with the front group extension of the focusing stopper. There are known devices that correct aberrations. An example of this is a zoom lens described in Japanese Patent Laid-Open No. 52-32342. However, in this lens system, the magnification of the rear group is different in each state of the wide, standard, and telephoto zoom lens, so the contribution to aberrations of the entire system is different in each state of zooming, so the aberrations are different in each state. The corrections are different and therefore it is difficult to find the appropriate air spacing and its variable amount that will provide adequate correction in all situations.

In addition, in a 2-group zoom, the rear group converging system is separated into two parts, and the aberrations when focusing on a close object point are corrected by changing the separation interval. Some lenses are known that correct aberrations. However, this zoom lens is actually a three-group zoom rather than a two-group zoom, and therefore has a complicated mechanism.

The present invention has been made in view of the above circumstances, and is a lens system composed of a front group diverging system and a rear group converging system, and has a lens system that minimizes fluctuations in aberrations during focusing in all zooming states. It provides a zoom lens that is as bright as /2.8 in the following conditions.

As mentioned above, the zoom lens of the present invention is a two-group zoom lens, of which the front group divergence system is extended during the rear group convergence system, and when focusing is performed, the asymmetrical lens changes in conjunction with the amount of extension. By setting the intervals so that the degree of contribution to aberration correction does not differ significantly in each state of zooming, a bright lens system with little variation in aberrations in all states of zooming can be achieved.

Furthermore, as for the variable air spacing of the rear group convergence system, a.

By selecting a focal or almost afocal air interval, that is, an interval in which the axial light beam is parallel to the optical axis, the back focus fB can be kept unchanged and a lens system with a simple structure can be obtained.

In this case, the degree of afocalness is determined by the ratio l fi71, where fi is the focal length in each zooming state of the lens system on the object side of the variable air gap, and f is the focal length of the entire system in that state. It is desirable that 1°i be 3.5 or more in each state.

In other words, this range is desirable because the amount of movement of fB can be kept below the variable amount i of the air gap.

Furthermore, if the variable air spacing during focusing is set to an afocal or almost afocal location as described above, the spherical aberration will remain unchanged at that variable air spacing, and if only the off-axis field curvature is considered, This is desirable because it facilitates correction of field curvature.

Next, examples of the zoom lens of the present invention will be shown. That is, it has a lens configuration as shown in FIG. 1 and has the following data.

Example r, = 136.89 d1 = 4.3 n, = 1.8044 ν, = 39.
58r2=493.22 d2=0.1 r3-102.53 d3=2.3 n2=1.79952 v2=42.2
4r4=23.11 d4=10.36 r5--191.0 d5=1.9 n=1.61272 v3=58.7
5r6'=38°98 d6=1.6 r7=35.87 d7=4.9 n'=1.8044 2 =39.5
8r8=490.18 d8=31.04~0.81 r9=53.95 d9=3.2 n5=1.69680 v5=55.5
2r, o--141,55 d. =2.7 r1□ =30.36 dl, =6.78 n6=1.69680 Shiro=5
5.52r1□=-36,77 d,□=3.37 n7=1.74320 Schiff=49
．． 31r, 3=-130,49 d13=2.5 r, 4=-37,62 d, 4=1.93 n8=1.7495OL'8=35
．． 27r, 5=34.22 d, 5=1.7 r, 6=301.36 d, 6=1.69 n, =1.80518 v9=25
．． 43r,,=41.20 d1□=1.79 r, 8==-71,62 d, 8=2.31 n1o=1.67790 ν, o
=55.33r, 9=-32,95 d, 9=0.1 r2o-129,72 d2o=3.8 nl, =1.51633 White 1.
=64.15r2□=-25.74 f=29~48, /2.6 However, rl, r2+..., r2 is the radius of curvature of each lens surface 1 a, l a21...l d20 is Thickness and air spacing of each lens, n, , n2.・・・・・・＋
"jl is the refractive index of each lens, shi□, shi2..., ν
1 is the Abbe number of each lens, and f is the focal length of the entire system.

In this embodiment, the air distance d8 between the front group i and the rear group ■ is changed by moving the front group divergent system I and the rear group convergent system ■ as indicated by the arrows at the top of FIG. Perform zooming. In addition, when focusing, the front group divergence system I is moved forward as shown by the arrow at the bottom of Fig. 2, and in conjunction with this, the front group 11a of the rear group convergence system H is moved rearward to infinity. Performs focusing from far to short distances. At this time, when focusing on an object point of 1 m, the air distance d15 between ■a and ■b is 1.42.

The aberration curves of this example are shown in FIGS. 3 to 5.

It's the same. Among these figures, Fig. 3 is an aberration curve diagram at an object point at infinity, and Fig. 4 is an aberration curve diagram when aberration correction is not performed at an object point of 1 m, that is, the interval d15 is not changed.
FIG. 5 is an aberration curve diagram when aberrations are corrected. In these figures, W stands for wide.

S is standard and T is tele.

As is clear from this example, when the front group divergence system is brought out and focusing is performed, the air interval that is changed in conjunction with this, and when it is not possible, the positive f is adjusted around the image plane.
The field curvature at short distances is corrected by providing a varying air spacing.

As explained above, the present invention reduces fluctuations in field curvature during focusing by changing the appropriate air spacing in the rear group convergence system, thereby increasing the angle of view at the wide end of 70° or more. We were able to realize a zoom lens with a wide-angle zoom of F/2.8 and a relatively simple construction.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the embodiment of the present invention, FIG. 2 is a diagram showing lens movement during zooming and focusing in the embodiment, and FIGS. 3 to 5 are aberration curve diagrams of the cyst example. be. Applicant Olympus Optical Industry Co., Ltd. Agent Hiroshi Mukai - Figure 1 Figure 2 Figure 4 Figure 5

Claims (1)

[Claims] In a two-group zoom lens that consists of a front group divergence system and a rear group convergent system, and which performs focusing by extending the front group divergence system, a variable air interval is provided in the rear group convergent system, and this air interval is adjusted to the front group divergence. A zoom lens having a short-range aberration correction mechanism, characterized in that the focusing mechanism is changed in conjunction with the movement of the focusing stop of the system.