JPS58215618A - Interchangeable variable power lens system - Google Patents

Abstract

PURPOSE:To obtain an interchangeable variable power lens system which consists of the 1st - the 4th lens groups having a positive, a negative, a positive, and a negative refracting power successively from an object side and varies in focal length in >2 states intermittently, by moving the 1st lens group on an optical axis and interchanging the 2nd lens group with another lens group with a different refracting power. CONSTITUTION:The lens system consists of the 1st lens group with the positive refracting power, the 2nd lens group with the negative refracting power, the 3rd lens group with the positive refracting power, and the 4tn lens group with the negative refracting power successively from the object side. While the 1st lens group is moved on the optical axis, the 2nd lens group having refracting powers N3 and N4 and Abbe numbers nu3 and nu4 are replaced with the lens group for magnification variation having refracting powers N'3 and N'4 and Abbe numbers nu'3 and nu'4 to vary the focal length of the whole lens system intermittently. The 2nd lightweight lens group with a small lens diameter is interchanged, so variation in focal length is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a variable power lens system that intermittently changes the focal length by 7il.

Conventionally, in 35 mm cameras, there has been a method for changing the focal length while making the lens system compact by changing the focal length intermittently, for example, as disclosed in Japanese Patent Application Laid-Open No. 56-132.
This is proposed in Publication No. 305 and the like. Also, U.S. Patent Nos. 3 and 3
No. 88,650 proposes a method of changing the magnification by inserting an auxiliary lens between the main lens system and the image and shifting the main lens system as one unit.

Furthermore, Japanese Patent Application Laid-Open No. 54-97423 proposes a method in which an auxiliary lens consisting of six lenses is placed behind the main lens system to change the magnification.

This auxiliary lens is large and cannot be said to be very desirable for making the entire lens system compact.

An object of the present invention is to provide a lens system in which the focal length can be changed intermittently at two or more points using a new method different from the conventional method.

A further object of the present invention is to provide a lens system that has a compact configuration, has an excellent zooming effect, and is well-corrected for aberrations.

A further object of the present invention is to maintain a constant position of the fringes or the positional relationship between the shutter position and the focal plane when changing the magnification, thereby simplifying the diaphragm mechanism or the shutter mechanism. This is what we are trying to achieve.

The features of the lens configuration for achieving the purpose of the present invention are, in order from the object side, a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a negative refractive lens group. The fourth lens group of the main lens system, which has four lens groups, is moved along the optical axis, and the second lens group has a negative refractive power different from the refractive power of the second lens group. The focal length of the entire lens system is changed intermittently by replacing the zoom lens group.

The lens system according to the present invention adopts a lens type similar to a telephoto type, and in order to minimize the overall length of the lens, the front part of the lens system has a strong positive refractive power and the rear part has a strong negative refractive power. ing. However, if the refractive power arrangement is made too strong, strong pincushion distortion may occur, and astigmatism will increase, which is undesirable in terms of aberration correction.

Therefore, as mentioned above, the third lens group is made with positive refractive power to maintain the balance of refractive power, and the fourth lens group is given an aspherical surface to compensate for the aberration caused by strengthening the negative refractive power of the fourth lens group. This has been corrected accordingly.

When changing the focal length, the lightweight second lens group with a relatively small lens diameter is replaced with the variable power lens group to facilitate changing the focal length.

Also, while maintaining the telephoto ratio by moving the lens group on the optical axis,
The free variable adjustment of aberration correction has been increased, achieving excellent aberration correction.

Furthermore, the lens system according to the present invention satisfies the following conditions in order to achieve good aberration correction both before and after the focal length is changed.

The focal length of the fourth lens group is f4, the focal length of the main lens system is fw, and the focal length after replacing the second lens group with a variable power lens group is ft. In the embodiments to be described later, fw is set such that the focal length is increased by the variable power lens group.

Here, conditional expression ([) is used to make the lens system more compact and to perform better aberration correction.If the lower limit of conditional expression (1) is exceeded, the variable power ratio ('ft and fw It becomes difficult to increase the ratio), and it becomes difficult to shorten the total length of the lens system.

If the upper limit is exceeded, it is advantageous to shorten the overall length of the lens system, but astigmatism worsens and it becomes difficult to sufficiently correct it even with the aspheric surface of the fourth lens group.

Furthermore, in the present invention, the second lens group is a laminated lens of two lenses with negative and positive refractive powers, and the second lens group and the variable power lens group are composed of two lenses with positive and negative refractive powers. The lens is made of a combination of two lenses, and the third lens group is a biconvex lens to effectively correct various aberrations before and after the focal length changes.

1'Especially the second lens group is lens %'He) Pez (
Since the -R sum tends to be positive before the change in focal length and fluctuate in the negative direction after the change, the refractive power of the bonded surfaces is strengthened to reduce fluctuations in the Petzval sum.

In the lens system according to the present invention, the object-side lens surface of the fourth lens is aspherical, and the shape of the aspherical lens is determined to satisfy the following conditions to achieve good aberration correction.

The shape of the aspherical surface is expressed by the X-axis in the optical axis direction and the Y-axis in the direction perpendicular to the round axis.
axis, the traveling direction of light is positive, the intersection of the apex of the lens and the The difference in the axial direction is ΔX, R is the paraxial curvature of the object side of the fourth lens group, R is ii++2 of the lens reference sphere defined by R=□, radius of curvature, ai is the aspherical side coefficient, bi Expressed as an expansion formula when is an aspherical odd coefficient, ΔX at the height of Y coordinate Rx O,7 is ΔX (0,7=1(), ΔX at the height of R×05 is △X [05R) When 7f.

The lens system according to the present invention strengthens the negative refractive power of the fourth lens group to increase the telephoto ratio and shorten the overall lens length, but various aberrations occur when the refractive power of the fourth lens group is strengthened. This deterioration is improved by introducing an aspherical surface to the object-side lens surface of the fourth lens group.

If the lower limit of conditional expression (2) is exceeded, the curvature of field at the periphery of the screen before the focal length change tends to be overcorrected, and if the upper limit is exceeded, the positive distortion after the focal length change is corrected well. It becomes difficult to do so.

If the lower limit of conditional expression (3) is exceeded, the curvature of field near the center of the screen after a change in focal length tends to be overcorrected, and if the upper limit is exceeded, distortion after a change in focal length cannot be adequately corrected. becomes difficult.

Focusing in the lens system according to the present invention can be performed not only by extending the first lens group or the entire lens, but also by moving only the second lens group or the variable power lens group. Furthermore, if the fourth lens group is used, it can be performed with a small amount of movement because of its strong refractive power.

The variable magnification lens group used in the present invention is generally built into the camera, but it is also possible to replace it externally, and the variable magnification lens group can be adjusted as far as space allows (v')2 It is also possible to incorporate more than one into the camera to vary the focal length.

With the above-described lens configuration, the present invention can achieve a lens system that is compact and capable of switching the focal length while maintaining excellent optical performance.

Next, numerical examples will be shown in which only the main lens system of the present invention is used and when a variable power lens group is attached.

Numerical example Let 111' be the refractive index and Atsube number of the glass of the first lens in order from the object side, and let 111' be the curvature radius of the first lens surface in order from the object side. , D1' are the thickness and air gap of the first lens in order from the object side, and j'Ji' and ν1' are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

In addition, the word value in the case of the main lens thread in the numerical examples is (W
The word value when the second lens group is replaced with a variable power lens group is shown as (T).

First example angle of view 2ω (Wl=55.102ωtTl=40.6
゜F number FWl = 3.5 F length ('
1'l = 3.9 focal length 1111 f (W) = 100
．． Of f'r) =] 41.0R4 two aspherical surfaces a+"0.81971X]0-", b+=0.28
761XIO-'at = -0,67279XIO
-', ht-0,41092X]0-'a+=0
．． 62195X]O, b+-0', 42070X10-
"a+=0.63071X]0,+]t=0.
58669XIO-”as-” (1,767
45X10 back focus b, f(Wl=51.422 b, f(Tl=
51.422 Telephoto ratio LtWl=i, 14 L(T+=0.92 Second example angle of view 2ω(W) = 55.2° 2ω(T)=
41.2°F number F interval (VIQ23.8
Floor F (Tl=3.9: aspherical a+-0, 92596X10-', b+'' 0.
22554X]0-”as=0.12492Xl
O-', b! = 0.18297XlO-'81 =
0.26036X10-'', bs=-0,16
584X]0- @a+ = 0.45951X10
1b* = 0.56395X10-”1 = 0.
10703XI O-” Pack focus b, f (W) =51.573 b, f
(T)=51.573 Telephoto ratio LtW+=1. J 3 L (T+=0.9
2

[Brief explanation of drawings]

1 and 2 are cross-sectional views of the main lens system according to the first embodiment of the present invention and a lens group when some lens groups of the main lens system are replaced, respectively. Figures 5 and 6 are diagrams showing various aberrations when the main lens system of Example 1 and some lens groups of the main lens system are replaced, respectively. FIG. 4 is a diagram showing various aberrations when the lens group of the lens is replaced. In the figure, ΔM is a meridional image plane, and ΔS is a zagital image plane. Patent applicant: Canon Co., Ltd. Double aberration distortion tax difference (%)

Claims (1)

[Scope of Claims] (1) In order from the object side, the lens group has a positive refractive power, the second lens group has a negative refractive power, the third lens group has a positive refractive power, and the fourth lens has a negative refractive power. A variable power lens that moves the first lens group of the main lens system having four lens groups upward by 5'1 jllll, and that the second lens group has a negative refractive power different from the refractive power of the second lens group. A patented switching type variable magnification lens system that allows the focal length of the entire lens system to be changed intermittently by changing groups. (2) When the focal length of the fourth lens group is f4, the focal length of the main lens system is fw, and the focal length after replacing the second lens group with a variable power lens group is %ft, t 0,0 1 6 < -- < 0.04 fw · 1 f41 The switching type variable magnification lens system according to claim 1 . (31 The tA4Jl lens group is a laminated lens of two lenses with negative and positive refractive powers, and the second lens group and the variable power lens group are a laminated lens of two lenses with positive and valve refractive powers. The switching type variable magnification lens system according to claim 2, characterized in that the lens is a combination lens, and the third lens group is a biconvex lens. (4) The object-side lens surface of the fourth lens group. is an aspherical surface with a concave surface facing the object side, and the shape of the aspherical surface is such that the X-axis is in the optical axis direction, the Y-axis is in the direction perpendicular to the optical axis, and the direction in which the light travels is positive. Find the origin at the intersection of the axes,
Let ΔX be the difference in the X-axis direction between the aspherical surface on the object side of the fourth lens group and the surface that is an extension of the spherical surface that contributes to determining the focal length, and R
is the paraxial radius of curvature of the object side surface of the fourth lens group, R is the radius of curvature of the lens reference spherical surface π + 2111 defined by R = □, al is the even coefficient of the aspheric surface, and bl is the coefficient of the valve sphere 2 Expressed by the following expansion formula, △ at the height of Y coordinate R x 07
When X is △X (07R) and △X at the height of R x 05 is △X (0,5n), w 1xio-'< lxX[o, sn <lXl0-''
A switchable variable magnification lens system according to claim 3, characterized in that it satisfies the following conditions: w.