JPH043103A - Real image type variable power finder optical system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a real image variable magnification finder optical system, and particularly to an external finder optical system provided separately from a photographing system. The objective lens and erector lens are used to change the magnification and the erector lens is used to change the magnification.
The present invention relates to a real-image variable magnification finder optical system suitable for, for example, still cameras and video cameras, in which the lens configuration of the lens is appropriately set to enable good viewfinder image observation.

(Prior Art) Conventionally, in cameras where the photographing system and finder optical system are configured separately, when the photographing system is a variable magnification system, a variable magnification finder with a configuration in which the viewfinder field magnification changes as the magnification changes is preferable for photographing. . Further, since the variable magnification finder is to be incorporated into the camera, it is preferable that the variable magnification finder is small and has a structure that allows a predetermined variable magnification ratio to be easily obtained.

The variable magnification finder optical system is constructed using a secondary imaging method, and the objective lens constituting the variable magnification finder optical system is composed of multiple lens groups. A real image type variable magnification finder optical system in which magnification is changed by moving a lens group on the optical axis is well known, and has been proposed, for example, in Japanese Patent Laid-Open No. 156019/1983.

Also, when changing the magnification of a part of the lens group that makes up the objective lens, it is possible to move the part of the lens group that makes up the erector lens by the same amount of movement as the amount of movement of the objective lens. A real-image magnification-variable finder optical system that performs magnification change has been proposed, for example, in Japanese Patent Publication No. 1912-1983.

Furthermore, the primary imaging plane by the objective lens is fixed and the erector
For example, a bifocal switching type real image variable magnification finder optical system in which the erector lens is switched at the position where the lens magnification becomes -51 and -17, f'i- (2 is the variable magnification ratio), is, for example, in practice. This is proposed in JP-A-59-186832.

In addition, while maintaining good optical performance of the finder system,
In order to reduce the size of the entire lens system while suppressing cost increases, a variable magnification finder optical system using an aspherical lens partially made of plastic material was developed, such as JP-A-62-7017.
This method has been proposed in Japanese Patent Application Laid-Open No. 1-1315], No. 0, and the like.

(Problems to be Solved by the Invention) However, in the real image type variable magnification finder optical system proposed in the above-mentioned Japanese Patent Application Laid-Open No. 61-156019, when variable magnification is performed by the objective lens, each lens constituting the objective lens If an attempt was made to configure the lens group by adding some limiting conditions to the amount of movement of the group, the problem would be that the objective lens would become larger as a whole, and the overall length of the lens would become extremely long.

In addition, with the real image type variable magnification finder optical system proposed in the above-mentioned Japanese Patent Publication No. 47-1912, it is difficult to adjust the variable magnification ratio accurately, and as the variable magnification ratio becomes large, it becomes difficult to see the view through the finder during variable magnification. There was a problem that it became difficult to keep the temperature constant.

In addition, the real image variable magnification finder optical system proposed in the above-mentioned Japanese Utility Model Publication No. 59-186832 has an erector lens at a position where the magnification of the erector lens is -F and 1/fT.
Since the lenses are switched, there is a problem in that continuous magnification cannot be obtained and it can only be used as a bifocal switch type.

Also, the above-mentioned Japanese Patent Application Laid-Open No. 62-7037 and Japanese Patent Application Laid-open No. 1-1
In Publication No. 31510, the optical performance, focal length, finder diopter, etc. change greatly due to large changes in the refractive index of the plastic material due to temperature changes, so it was necessary to take measures in response to some kind of environmental change.

The present invention relates to a real image type variable magnification finder optical system, in particular, to change magnification using an objective lens and an erector lens, and to appropriately set the lens configuration of an erector lens having an aspherical lens partially made of a plastic material. According to
For example, still cameras, etc., which have little change in the viewfinder diopter due to temperature changes, have a relatively short overall lens length despite having a high zoom ratio of about 4, and have high optical performance with good correction of various aberrations. The purpose of the present invention is to provide a real-image variable magnification finder optical system suitable for video cameras and the like.

(Means for Solving the Problems) The real image type variable magnification finder optical system of the present invention uses an erector lens to secondarily form an inverted first finder image formed on a primary imaging plane by an objective lens. When re-forming an erect second finder image on the image plane and observing the second finder image on the secondary image plane through an eyepiece,
While moving the objective lens toward the object side, the erector
The lens is moved at a speed different from that of the objective lens, and the first finder image formed by the objective lens is re-imaged on the secondary imaging plane to perform magnification change, and The erector lens consists of four lenses, in order from the object side: a positive first lens, a positive second lens, a negative third lens, and a positive fourth lens made of a plastic material with an aspherical surface on the object side. , where fi is the focal length of the i-th lens, fe is the focal length of the erector lens, and B is the fourth-order aspherical coefficient of the aspherical surface of the first lens, then 4< f1/
f2 <7...(1) 1, s<(
f:z+f4)/(-2f3)<2.5...(
2) It is characterized by satisfying the following condition: -5<B-fe<-2-----(3).

(Example) FIGS. 1A, 1B, and 1C are cross-sectional views of lenses of a real image variable magnification finder optical system of Numerical Example 1, which will be described later, of the present invention. In the same figure, (A) wide-angle end, (B)
(C) shows the middle position, and (C) shows the telephoto end.

In the figure, 1 is an objective lens, 2 is a primary imaging plane, and an inverted first finder image is formed by the objective lens 1. Reference numeral 4 denotes an erector lens which corrects the inverted first finder image formed on the primary image forming surface 2 to an erect normal image and forms the image at a predetermined magnification on the secondary image forming surface 6 to be described later. . 6
is a fixed secondary image forming surface, and an erected second finder image is formed by the erector lens. 7 is an eyepiece, and 8 is an eye point of the observer.

In this embodiment, a light beam from an object (not shown) is condensed by an objective lens 1, and an inverted first finder image is formed on a primary imaging plane 2. The light beam based on the first finder image formed on the primary image forming surface 2 is relayed by the erector lens 4, whereby a second finder image of an erect image is re-imaged on the secondary image forming surface 6. ing. A second finder image formed on the secondary image forming surface 6 is observed from the eye point 8 through the eyepiece lens 7.

Next, when changing the magnification from the wide-angle end to the telephoto end, the objective lens 1 is moved toward the object side as shown by the arrow in the figure.

Accordingly, the erector lens 4 is changed to the objective lens 1.
The inverted first finder image formed on the primary imaging plane 2 is moved toward the object side as shown by the arrow so as to be re-imaged on the fixed secondary imaging plane 6 at a predetermined magnification. And 2
The second finder image of the erect image re-imaged on the next imaging plane 6 is observed from the eyepoint 8 through the eyepiece 7 at a predetermined magnification.

In this embodiment, with this configuration, the erector
The finder magnification is changed in accordance with the change in the paraxial lateral magnification of the lens 4.

Also, at this time, the lens configuration of the erector lens 4 is set as described above, and the conditional expressions (]), (2), (
3). This achieves high optical performance by shortening the overall length of the lens and reducing changes in finder diopter due to temperature changes when using a lens made of plastic material.

In this embodiment, the rear lens 1a constituting the objective lens 1 is an optical field lens that efficiently guides the light beam based on the first finder image formed on the primary imaging surface 2 to the rear erector lens 4. It's working.

Further, the front lens 7a constituting the eyepiece lens 7 functions as a field lens that efficiently guides the light beam based on the second finder image formed on the secondary image forming surface 6 to the eye point 8 via the rear lens. It has an optical effect.

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (1) relates to the ratio of the refractive powers of the first lens and the second lens, and is designed to maintain good optical performance when the first lens is mainly composed of an aspherical lens made of plastic material, while also being resistant to temperature changes. This is to reduce the accompanying change in viewfinder diopter.

If the upper limit is exceeded and the refractive power of the first lens becomes too weak, the refractive power of the second lens will become strong and R will become tight, making it difficult to manufacture. Furthermore, if the lower limit is exceeded and the refractive power of the first lens becomes too strong, the sensitivity of the finder diopter due to temperature changes will increase and the change in finder diopter will increase, which is not good.

Conditional expression (2) is used to appropriately set the ratio of the refractive power of the third lens to the sum of the refractive powers of the second lens and the fourth lens, and to correct various aberrations in a well-balanced manner. Conditional expression (2)
If the refractive power of the third lens becomes too strong or weaker than the sum of the refractive powers of the second and fourth lenses, various aberrations such as coma and curvature of field will increase, and these should be well corrected. It's getting difficult.

Conditional expression (3) appropriately sets the aspherical amount of the first lens,
This is to satisfactorily correct various aberrations of the entire screen. If Condition (3) is not satisfied and the amount of aspherical surface becomes too large or too small, it will be difficult to correct spherical aberration, coma, etc. in a well-balanced manner, and it will be difficult to maintain good optical performance over the entire screen. It's coming.

Next, lens sectional views of specific lens structures applicable to the erector lens according to the present invention are shown in FIGS. 2(A) to 2(D).

Figure 2 (^) corresponds to Numerical Example 1.2 to be described later, and shows a meniscus-shaped positive first lens made of a plastic material with a convex surface facing the object side and whose convex surface is aspheric, both lens surfaces. It consists of a positive second lens having a strong refractive power and made of a glass material with a convex surface, a negative third lens with both concave lens surfaces, and a positive fourth lens with both convex lens surfaces.

Figure 2 (B) shows the first lens and second lens in Figure 2 (A).
This is a case where the lenses are cemented together and are configured with four lenses in three groups.

FIG. 2(C) shows a case where the positive first lens in FIG. 2(A) is constructed by forming a lens in which both lens surfaces are convex.

FIG. 2(D) shows a case in which the positive first lens in FIG. 2(A) is constructed from a meniscus-shaped lens with a convex surface facing the eyepiece side.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the i-th lens surface in order from the object side, D
l is the thickness and air distance of the i-th lens from the object side, Ni
and υi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of the light is positive, R is the paraxial radius of curvature, A, B, C,
When D and E are each divided by their aspherical coefficients, it is expressed as +DH'+EH''.

\ Numerical Example Pupil Diameter φ R] -12,63 R2--6,50 R3-10,58 R4-99,60 R5-7,27 R6-8,97 87~9807 R8--14,09 R9・-105,28 RIO-6,46 R1-26,39 R2--13,11 Ri3- 18.93 Ri4- ■ R5 mat 30.00 R6--30,79 R7-Eye point 3 2ω-55,4° 〜14.3゜D l-
6,0N 11-1.49171 v l-57
,402-13,0 D 3- 4.0 N 2-1.49+71
ν 2-57.4D4・Variable D 5・2.0 N 3・], 49171 v
3-57.4D6・0.2 D 7-2.9 N 4-], 5J633 v 4
-64. ID 8-2.37 D 9-2.00 N 5 1.80518 v
51=25.4DIO-3,36 01-4,ON &-1.5]633 v 6-6
4.1DI2 ~ variable [113-3,0N 7-1.49]71 v
7-57.4D+4-29.35 D 5-3.5 88-1.4gl71 ν B-5
7,4D 6-16.0 Aspheric coefficient lens surface R2 A-OB-6,78x 10-' D 4.46 Xl0-' C--6,68xlO-6 E・0 Lens surface R5 A~OB- 5,33X1O-' D-3,16X10-8 Lens surface R15 A-OB--1,45x 10-' D--5.89 xlO-' fl/f2 5.03 (f2◆f4)/(-2f3 )・3.83β・f, 3
--3.7 C--2,22Xl0-6 E--3,27xlO-9 C-1,16xlO-' E-1,01xlO-8 Aspheric coefficient lens surface R2 ^-OB-6,75x IQ- ' D・4.46 xlO-' C-6,68 1O-6 Lens surface R5 ^-OB--5,33xlO-' O~3. ] 6
-3.52 C--2,22x 1O-6 E--3,27xlO-9 C-1,16Xl0-' E・ 1.01 Xl0-' Numerical example pupil diameter φ3 R1-12,630]-6 , OR2--6, 5002-13, OR3- 10.58 D 3- 4. OR4
-99,60D 4-Variable R5-7,27D 5-2.0 R6-8,97D 6-0.2 R7-9,07D7・2.9 R8--14,09D 8-2.37 R9-105 ,28D 9-2.0O RIO-6,46DIO-3,36 R11-19,62Dl! -4,0 R2--13,54 DI2 variable R] 3- 18.93 D13 3. OR4-oo
D14-29.35 RI5- 30.00 015-3.5R]6--30
．． 79 018-16.0R17-Eye point 2ω~55.4°~14.3°N 1~1.49171 ν 2-1.49] 71 3-1.49171 4-1.51633 5-1.80518 6 -1.4917] 7-1.49171 N 8-1.49171 ] -57,4 2-57,4 4-64,1 5-25,4 6-57,4 7 irises 57.4 8-57. 4 (Effects of the Invention) According to the present invention, the objective lens and the erector lens are moved independently on the optical axis to change the magnification, and the configuration of the erector lens is set as described above, thereby achieving high variable power with a simple configuration. It is possible to achieve a real image variable magnification finder optical system that can easily obtain a magnification ratio and has high optical performance with little change in finder diopter due to environmental changes.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a lens according to a numerical example of the present invention, FIGS. FIG. 4 is a diagram showing various aberrations of Numerical Example 1.2 of the present invention. In FIGS. 1, 3, and 4, (A) shows the zoom position at the wide-angle end, (B) shows the zoom position in the middle, and (C) shows the zoom position at the telephoto end. In the figure, 1 is an objective lens, 2 is a primary imaging surface, 4 is an erector lens, 6 is a secondary imaging surface, 7 is an eyepiece, and 8 is an eye point. N Fig. (A Fig. Spherical aberration fjiop) Astigmatism difference fdioP) Distortion # (% Fig. Spherical aberration (diop) Astigmatism (droll) Distortion aberration (%) Fig. B) Fig. Spherical aberration (diop) Astigmatism (diop) Distortion (%)

Claims (1)

[Claims] (1) An inverted first finder image formed on a primary imaging plane by an objective lens is re-imaged as an upright second finder image on a secondary imaging plane by an erector lens,
When observing the second finder image on the secondary image forming surface through the eyepiece, the objective lens is moved toward the object side, and the erector lens is moved at a speed different from that of the objective lens. The magnification is changed by re-imaging the first finder image formed by the lens on the secondary image forming surface, and the erector lens is made of plastic with an aspherical surface on the object side lens surface in order from the object side. It has four lenses: a positive first lens, a positive second lens, a negative third lens, and a positive fourth lens made of a material, the focal length of the i-th lens is fi, and the focal length of the erector lens is f_e
, when the fourth-order aspherical coefficient of the aspherical surface of the first lens is B, 4<f1/f2<7 1.5<(f2+f4)/(-2f3)<2.5-5<
A real image type variable magnification finder optical system that satisfies the following condition: B.f_e^3<-2.