JPH01319725A - Variable power finder optical system - Google Patents

Abstract

PURPOSE:To vary a magnification and eye pint with compact and simple means by constituting an eyepiece lens of 3 lens groups and moving two pieces of the 1st lens group and the 2nd lens group in opposite directions on the optical axis, thereby executing variable power. CONSTITUTION:The eyepiece lens 40 is made of the 3-group 4-element constitution consisting of the 1st lens group 10 which is two pieces of positive lenses, the 2nd lens group 20 which is a piece of negative lens, and the 3rd lens group 30 which is a piece of positive lens. The 3rd lens group 30 is fixed and two pieces of the lenses 4, 5 of the 1st lens group are moved integrally on the optical axis toward a pentagonal roof prism 3 and the 2nd lens group 20 is moved in the direction opposite thereto, by which the low magnification is changed to a high magnification. The variable power finder is obtd. while the finder diopter is maintained constant by moving the 1st lens group and the 2nd lens group in the directions opposite from each other. The eye point 8 can be moved backward by decreasing the finder magnification. The finder image good for a spectacle user as well is thus provided.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a variable magnification finder optical system, and in particular, to a variable magnification finder optical system in which a part of the lens group of the eyepiece lens arranged behind the exit surface of a penta roof prism is moved on the finder optical axis. Accordingly, the present invention relates to a variable magnification finder optical system having a compact and simple configuration that changes the finder magnification while keeping the finder diopter constant.

(Prior art) Conventionally, in the finder optical system of a single-lens reflex camera, the object image on the focus plate is focused through a penta roof prism at a position of about -1 dayopter with the eyepiece lens, and the object image at this time is The observation eye is placed at a position (eyepoint) a certain distance behind the eyepiece through the eyepiece. In addition, the viewfinder magnification is simply determined by the ratio of the focal length of the objective lens (also called the "taking lens") and the eyepiece. From the optical path length of the roof prism, the focal length of the eyepiece is approximately 60 mm, so if a standard lens with a focal length of 50 mm is used as a photographic lens, for example, the magnification will be approximately 0.83 times.

On the other hand, in recent years, not only automatic exposure but also automatic focusing have been developed in negative-eye reflex cameras, and a wide variety of displays within the viewfinder are required.

Therefore, in order to observe the subject image and the display in the finder without vignetting, the pentagonal roof prism must be made larger, and as a result, the finder magnification tends to decrease.

Conventionally, various variable magnification finder optical systems in which the finder magnification of the finder optical system is variable have been proposed for single-lens reflex cameras. For example, a method is known in which an attachment lens is attached to the rear of the eyepiece and the viewfinder magnification is changed to enlarge a part of the subject image to observe the shadow field.

In addition, JP-A-56-11427 and JP-A-57-22
In Publication No. 225 and the like, a lens for changing the magnification is inserted into a part of the eyepiece lens system to change the finder magnification.

This method requires a place for the lens to be evacuated, resulting in space problems and the drawback that the entire device cannot be made more compact.

On the other hand, there is a method of adjusting the diopter by making the eye point variable in the finder optical system, for example, in Japanese Patent Laid-Open No. 57-13.
This is proposed in the 0022 publication. In this publication, an attachment lens is attached to the rear of the eyepiece lens to make the eye point variable and adjust the diopter.

However, since the finder optical system described in the same publication has a variable eye point, attaching an attachment lens behind the eyepiece lens results in poor operability and makes it impossible to make the device as a whole compact. There were some drawbacks.

(Problems to be Solved by the Invention) In the present invention, when observing a finder image with an eyepiece disposed behind the exit surface of a pentagonal roof prism, the eyepiece is composed of three lens groups. At least one lens in the first lens group and the second
By moving the lens groups in opposite directions on the viewfinder optical axis, the viewfinder magnification and eyepoint can be varied while keeping the viewfinder diopter constant with simple operation, and the compact design maintains good optical performance as the magnification changes. The purpose of the present invention is to provide a variable magnification finder optical system with a simple configuration.

(Means for Solving the Problem) In a variable magnification finder optical system in which a finder image formed on a focusing plate by a photographing lens is observed through a penta roof prism with an eyepiece while changing the finder magnification, the eyepiece is A first lens group having a positive focal length having at least two positive lenses and a second lens group having a negative focal length having at least one negative lens in order from the penta roof prism side, The finder magnification is made variable by moving at least one lens A in the lens group and the second lens group in opposite directions on the finder optical axis.

(Embodiment) FIGS. 1 to 3 are optical path diagrams of essential parts of a first embodiment, each showing an expanded state of the variable magnification finder optical system of the present invention.

Figure 1 shows the condition when the viewfinder magnification is low;
The figure shows the state when the finder magnification is medium, and FIG. 3 shows the state when the finder magnification is high.

In FIGS. 1 to 3, reference numeral 1 denotes a focus plane, and a finder image is formed by a photographing lens (not shown). 2 is a condenser lens, and 3 is a penta-roof prism that creates inverted images vertically and horizontally, and is shown as an expanded glass block for simplicity.

Reference numeral 40 denotes an eyepiece lens, which is composed of a first lens group 10, a second lens group 20, and a third lens group 30.

The first lens group 10 is composed of two positive lenses, a single lens 4 having a positive refractive power and a single lens 5 having a positive refractive power.

The second lens group 20 is composed of a single lens 6 having negative refractive power.

The third lens group 30 is composed of a single lens 7 with positive refractive power. 8 is an eye point for observing the finder image.

In this embodiment, the eyepiece lens 40 is composed of a first lens group 10 consisting of two positive lenses and a second lens group 10 consisting of one negative lens.
Third lens group 3 consisting of lens group 20 and one positive lens
0, the third lens group 30 is fixed, and the two lenses 4 and 5 of the first lens group 10 are integrated toward the side of the pentagonal roof prism 3 on the viewfinder optical axis, and the second lens The group 20 is moved toward the side of the third lens group 30 and both lens groups are moved in opposite directions to change the viewfinder magnification from low magnification to high magnification, and the eye point 8 is moved.
The finder image formed on the focusing plate 1 is observed.

In particular, in this embodiment, a finder image with high optical performance is obtained by arranging a fixed third lens group 30 and favorably correcting variations in various aberrations during zooming.

Furthermore, by arranging the fixed third lens group, the exit surface of the eyepiece lens 40 is fixed, making it easier to observe the finder image.

The focal length of the variable magnification finder optical system in this example is 62.2 mm at low magnification in Figure 1, 57.5 mm at medium magnification in Figure 2, and 53.2 mm at high magnification in Figure 3.
For example, when a standard lens with a focal length of 50 mm is attached as a photographic lens, the finder magnifications are approximately 0.80 times, 0.87 times, and 0.94 times, respectively.

Also, the focal length f of the first lens group 10 of the eyepiece 40,
is f, = 35, 3 mm, the focal path R2 of the second lens group 20 is f2 = -44, 3 mm, and the focal length f3 of the third lens group 30 is f3 = 135.4 mm.

Next, the principle of variable magnification of the variable magnification finder optical system of the present invention will be explained using FIGS. 19 and 20.

In Figures 19 and 20, 40A is the eyepiece lens, IO
A is a first lens group with positive refractive power, 20A is a second lens group with negative refractive power, and 30A is a third lens group with positive refractive power.

FIG. 19 shows the optical arrangement before the finder magnification is changed, that is, when the magnification is low, and FIG. 20 shows the optical arrangement after the finder magnification is changed, that is, when the magnification is high.

1 is the focus plane, 8 is the eye point, and 1' is the virtual image position of the focus plane 1 by the eyepiece lens 40A.

In this embodiment, for simplicity, the first lens group 10A, the second lens group 20A, and the third lens group 30A are made of thin lenses, and the first lens group 10A and the second lens group 20A are moved in opposite directions on the viewfinder optical axis. The magnification is changed from low to high magnification.

Now, assume that the refractive power (reciprocal of the focal length) of the first lens group 10A is φA, the refractive power of the second lens group 20A is φB, and the distance e between both lens groups is changed to e+Δe. At this time, as shown in FIG. 19, the eyepiece 4 when the distance is e.
If the refractive power at 0A is φT, and the refractive power of the eyepiece 40A at the interval e+Δe shown in FIG. 20 is φW, then φT, φ
W is φT −φA + φB−e ・φA ・φB
...(1) φW-φA + φB-(e+Δe)
It is expressed as φA−φB−·−(2).

Therefore, as shown in both figures, the first lens group 10 of the eyepiece
When A and the second lens group 20A are composed of lens groups with different focal length signs, the refractive power of the entire eyepiece can be increased (the focal length can be shortened) by increasing the distance between both lenses. .

FIG. 21 is a schematic diagram showing the principal point position of the variable magnification finder optical system shown in FIGS. 19 and 20.

In this figure, the same elements as in FIGS. 19 and 20 are given the same reference numerals, 9 is the front principal point position, and 9' is the rear principal point position.

In the same figure, the distance between the focal plane 1 and the front principal point position 9 is
The distance between eye point 8 and rear principal point position 9' is d, and the distance from eye point 8 to virtual image position 1' of focus plane 1 is D.
, the following equation holds true when the refractive power of the eyepiece is φ.

The viewfinder diopter is expressed in 110,007 D diopters. (However, D shall be expressed in mm.) Normally, in the variable magnification finder optical system of an eye reflex camera, the finder diopter is set to approximately -1 dayopter, so from eye point 8 to virtual image position 1' of focal plane 1. The distance is D'=i=1000vu, and in the figure, it is generally determined that D>d.

That is, in order to prevent the finder diopter from changing due to changes in the refractive power of the eyepiece, the distance l from the focal plane 1 to the front principal point position increases as the refractive power φ of the eyepiece increases.
l! This means that tL must be shortened.

Further, when LT is the distance between the front principal point of the variable magnification finder optical system and the focal plane 1 shown in Fig. 19, and LW is the interval between the front principal point of the variable magnification finder optical system and the focal plane 1 in Fig. 20. , LT, and LW are each obtained by paraxial tracking, LT −□ ・・・・・・・・・・(4) 1−eφ
B LW -□ ......(5) It is determined by 1-(e+Δe)φB.

Here, if the refractive power φA of the first lens group 10A and the refractive power φB of the second lens group 20A are of different signs, (1), (2
) From the formula, φT becomes φW, so in order to keep the finder diopter constant in the variable magnification finder optical system in Fig. 19 and the variable magnification finder optical system in Fig. 20, LT is obtained from the formula (3).
>Must be LW. Therefore (4), (5
), the refractive power φB of the second lens group 20A is φBoo,
That is, it must have negative refractive power.

Based on this principle, in this embodiment, FIGS. 19 and 20
As shown in the figure, the configuration of the eyepiece 40A is made up of a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power in order from the penta-roof prism side. A variable magnification finder that has a three-group structure and can vary the finder magnification while keeping the finder diopter constant by moving the first lens group and the second lens group in opposite directions on the finder optical axis when changing the magnification. The optical system has been achieved.

In particular, in this embodiment, the distance from the focal plane to the front principal point of the variable magnification finder optical system is shortened in response to the shortening of the focal pressure Rf of the entire variable magnification finder optical system.

To give a specific example, in Fig. 1, f = 62.2 mm, L = 57
．． 901111. In Figure 2, f=57.5mm.

L=53.7mm, f=53.2mm in Figure 3.

L=49.8mm to prevent changes in the finder diopter.

In this embodiment, in order to easily change the viewfinder magnification while helping to change the viewfinder diopter, and to further correct the occurrence of various aberrations at this time, the first
In order to reduce various aberrations occurring in the positive lenses of the lens group, a third lens group with a fixed positive focal length is provided, and the focal length of the first lens group 0 is f1, and the third lens group 3
When f3 is a focal length of 0, it is preferable to satisfy the condition fl < f3.

4 to 6 are diagrams of various aberrations corresponding to Numerical Example 1, which will be described later, in the variable magnification finder optical system of the first example of the present invention.

These aberration diagrams correspond to the finder optical system in the low magnification state, medium magnification state, and high magnification state shown in FIGS. 1 to 3, respectively.

In the aberration diagram, M is a meridional focal line and S is a sagittal focal line.

7 to 9 and 10 to 12 are schematic diagrams showing the effects of the variable power finder optical system of the present invention, respectively.

7 to 9 are explanatory diagrams showing changes in magnification of a finder image in the first embodiment of the present invention, and correspond to low magnification, medium magnification, and high magnification in this order.

FIGS. 10 to 12 are schematic diagrams showing changes in the eye point according to the first embodiment of the present invention, and correspond to low magnification, medium magnification, and high magnification, respectively.

In Figures 10 to 12, 1 is a focusing plane, 2 is a condenser lens, 3 is a penta roof prism, and 40 is an eyepiece lens, the first lens group having two positive lenses and one negative lens. It is composed of four lenses in three groups: a second lens group with a positive lens, and a third lens group with one positive lens. 8 is an eye point for observing the finder image.

Incidentally, FIGS. 9 and 12 each show the state when the display in the finder is erased.

In this embodiment, the finder magnification is changed by moving the first lens group and the second lens group that constitute the eyepiece in opposite directions on the finder optical axis, and as shown in FIGS. 10 to 12. As shown, by effectively utilizing the pentagonal roof prism, the finder magnification is increased to provide a finder image that is easy for observers who wish to observe only the subject image at high magnification.

Furthermore, by reducing the finder magnification and moving the eye point 8 backward, a finder image that is less likely to be eclipsed and easy to see is provided even for an observer who places his or her viewing eye relatively backward.

FIGS. 13 to 15 are optical path diagrams of essential parts showing the state when the optical system of the second embodiment of the variable magnification finder optical system of the present invention is developed.

In this figure, the same elements as in FIG. 1 are designated by the same reference numerals.

FIG. 13 shows a state where the finder magnification is low, FIG. 14 shows a state where the finder magnification is medium, and FIG. 15 shows a state where the finder magnification is high.

In this embodiment, the eyepiece lens 40 is composed of a first lens group 10 consisting of two positive lenses and a second lens group 10 consisting of one negative lens.
It is composed of four lenses in three groups: a lens group 20 and a third lens group consisting of one positive lens. When changing the magnification, one lens A in the first lens group 10, that is, the single lens 5, is moved toward the pentagonal roof prism 3 on the viewfinder optical axis, and the second lens group 20 is moved toward the third lens group 30. The finder image formed on the focusing plate 1 by an unillustrated photographic lens is observed at the eye point 8 by moving the finder in opposite directions to change the finder magnification from a low magnification to a high magnification.

In this embodiment, the fixed single lens 4 in the first lens group 10 and the fixed third lens group 30 are arranged to reduce aberration fluctuations during zooming, to satisfactorily correct various aberrations, and to achieve high Obtains a viewfinder image with optical performance.

Furthermore, by arranging the fixed single lens 4 and the fixed third lens group, the exit surface of the eyepiece lens 40 is fixed, making it easier to observe the finder image.

In this embodiment, the focal length of the variable magnification finder optical system in the states shown in FIGS. 13 to 15 is the first one.
62.4+nm at low magnification in Figure 3, 57.8+nm at medium magnification in Figure 14, and 53.8nm at high magnification in Figure 15.
5aon, for example, if the focal length is 5aon as a photographic lens.
01! When a standard lens of I [[l is attached, the viewfinder magnification is approximately 0.80x, 087x, and 0.9
It has tripled.

In this embodiment, the focal length f of the single lens 5 in the lens group of the eyepiece 40 is f = 60.0 mm, the focal path 11 t 2 of the second lens group is f2 = -50.5 mm,
The focal length f3 of the third lens group is f3=111.4 mm.

In addition, in this embodiment, in order to keep the finder diopter constant so that it does not change when the finder magnification is changed, the optical principle of the variable magnification finder optical system described above (Figs. 19 to 2) is used.
Figure 1) is used.

In addition, in order to shorten the focal path @f of the entire variable magnification soyunder optical system, the distance l from the focal plane to the front principal point of the variable magnification finder optical system! ! IL is shortened.

Specifically, in FIG. 13, f=62.4+nm, L=
58.1mm, f=57.8mm in Figure 14, L=5
3.9mm, f=53.5+n+n, L= in Fig. 15
This prevents the finder diopter from changing.

In this embodiment, in order to easily change the finder magnification, the focal length of the single lens 5, which is the movable lens A in the first lens group 10, is set to fA, and the focal length of the third lens group 30 is set to fA. When the distance is f3, it is preferable to satisfy the condition fA < f3.

16 to 18 are diagrams of various aberrations corresponding to Numerical Example 2 in the variable magnification finder optical system according to the second example of the present invention. These aberration diagrams are shown in FIGS. 13 to 15, respectively.
It corresponds to the finder optical system in the low magnification state, medium magnification state, and high magnification state shown in the figure.

FIGS. 22 to 24 are optical path diagrams of essential parts showing the state when the optical system of the third embodiment of the variable magnification finder optical system of the present invention is developed.

In this figure, the same elements as in FIG. 1 are given the same reference numerals.

FIG. 22 shows a state where the finder magnification is low, FIG. 23 shows a state where the finder magnification is medium, and FIG. 24 shows a state where the finder magnification is high.

In this embodiment, the eyepiece lens 40 is composed of a first lens group 1o consisting of two positive lenses and a second lens group 1o consisting of one negative lens.
The lens group 20 is composed of three fixed protective glasses 7 in two groups. When changing the magnification, one lens A in the first lens group 10, that is, the single lens 5, is moved toward the side of the pentagonal roof prism 3 on the optical axis of the finder, and the second lens group 2o
The viewfinder magnification is changed from low magnification to high magnification by moving the protective blade lath 7 in opposite directions, and the viewfinder image formed on the focusing plate 1 by a photographing lens (not shown) is observed at the eye point 8. ing.

In this embodiment, a fixed protective glass 7 is disposed on the exit surface of the eyepiece lens 40, making it easier to observe the finder image.

In this embodiment, the focal length of the variable magnification finder optical system in the states shown in FIGS. 22 to 24 is the second
59.3 mm at low magnification in Figure 2, 55.7 mm at medium magnification in Figure 23, 52.4 m at high magnification in Figure 24
m, and for example, as a photographic lens, the focal length is 5011
When the 1111 standard lens is attached, the viewfinder magnification is approximately 0.84x, 0.90x, and 0.95x, respectively.

In this embodiment, the focal length f of the first lens group of the eyepiece 40 is f=36.8 mm, and the focal length f2 of the second lens group is f2=-73,6+n+n.

In addition, in this embodiment, in order to keep the finder diopter constant so that it does not change when the finder magnification is changed, the optical principle of the variable magnification finder optical system described above (Figs. 19 to 2) is used.
Figure 1) is used.

Furthermore, in order to shorten the focal length f of the entire variable magnification sounder optical system, the distance l1IL from the focal plane to the front principal point of the variable magnification finder optical system is shortened.

Specifically, in Fig. 22, f = 59.3 mm, L = 5
5.3mm, f=55.7mm, L=52 in Figure 23
．． 1mm, f=52.4mm, L=49.
This prevents the finder diopter from changing.

FIGS. 25 to 27 are diagrams of various aberrations corresponding to Numerical Example 3 in the variable magnification finder optical system according to the third example of the present invention. These aberration diagrams are shown in FIGS. 22 to 24, respectively.
It corresponds to the finder optical system in the low magnification state, medium magnification state, and high magnification state shown in the figure.

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
i is the i-th lens thickness and air distance from the object side, Ni
and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side.

Note that the first aspect of the present invention. Second. In the third embodiment, the optical path diagram and aberration diagram show that the distance between the focal plane 1 and the condenser lens 2 is 0.
．． 5mm, the distance between the eyepiece 30 and the eyepoint 8 is 1
It is drawn as 6.0mm.

Numerical Example I R1” co D 1- 5.2 N 1
-1.49171 v 1-57.482 Rumor -65
,00D 2- 1.2 R3-oo D 3-80.0 N 2-1
．． 51633 v 2-64. lR4-00D4-
Variable R5 = 462.71 0 5- 3.0
N 3-1.77250 v 3@49.
6R6-121,81D B-0,5 R7-jo, 56o 7- 4.0 N 4-1
．． 83400 ν4-37.2R8-112,61
08 = Variable R9 Snow 759.40 0 9- 1.0
N 5-1.76182 ν 5- 26
．． 6RIO-32, 29D10- Variable R11-126, 38Dll electric 2.0 N
6-1.51633 ν 6- 64. lR1
2-155,56 Numerical Example 2 R111 (1) DI-5,2N1 item 1.49171
νl-57,4R2--65,0002-1,2 R3=oo D 3-80. ON 2-1.5
1633 v 2-64. IR4 proverb 0004-
1.0 R5-142,6905-3,0N 3-1.7725
0 ν3-49.686-255.44 D 6・
Variable R7-30, 31D 7-4.0 N 4-1
．． 69680 ν4-55.5R8-104,34
08・Variable R9-125,7509-1,0N 5-1.7618
2 ν5-26.6RIO-29,35010・
Variable n1l-57, 50D11~2.0 N 6-1
．． 51633 Shiro・64.1R12-(1) Numerical Example 3 R11-(to) DI-5,2' N1-1.49
171 νl-57,4R2--65,00D 2
- 1.2 R3-oo D 3-80.0 N 2-1
．． 51633 v 2 = 64. IR4～
D4- Variable R5-124,07D 5- 3.0 N 3-
1.69680 ν3-55.5R6-129,0
3D 6-0.5 R7-36, 62D 7 4. ON 4-1.772
50 ν4-49.6R8-154,79D 8・
Variable R9-106, 27D 9- 1.2 N 5-
1.76182 υ5-26.5RI0・ 36.
53 DIO-Variable RII=oo Dll-1,0N6-1.516
33 Jiro 64. lR12=ω (Effects of the Invention) According to the present invention, the eyepiece includes a first lens group having a predetermined lens and having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a positive refractive power. consisting of three lens groups, at least one lens in the first lens group and one lens in the second lens group.
By moving the lens groups in opposite directions on the viewfinder optical axis to change the magnification, the finder magnification and eye point can be made variable with a compact configuration and simple means, and the optical performance that accompanies the change in magnification can be improved. It is possible to maintain a good finder image for an observer who wants to maintain a good view and observe only the subject image at high magnification, and also for an observer who wants to shift the eye point backward because he or she uses glasses, etc. A variable magnification finder optical system with a simple configuration can be achieved.

[Brief explanation of the drawing]

Figures 1 to 3 are optical path diagrams at low magnification, medium magnification, and high magnification when the variable magnification finder optical system of the first embodiment of the present invention is expanded, and Figures 4 to 6 are optical path diagrams respectively shown in the figure. First invention
Various aberration diagrams at low magnification, medium magnification, and high magnification of the variable magnification finder optical system of the embodiment, and FIGS. 7 to 9 show finder images at low magnification, medium magnification, and high magnification of the first embodiment of the present invention, respectively. 10 to 12 are schematic diagrams of the variable magnification finder optical system showing changes in the eye point at low, medium, and high magnifications according to the first embodiment of the present invention, respectively. 1
3 to 15 are optical path diagrams at low magnification, medium magnification, and high magnification when the variable magnification finder optical system of the second embodiment of the present invention is developed, and FIGS. 16 to 18 are optical path diagrams of the variable magnification finder optical system of the second embodiment of the present invention Various aberration diagrams at low magnification, medium magnification, and high magnification in the variable magnification finder optical system of the second embodiment, and FIGS. 19 and 20 are schematic diagrams showing the optical principle of the variable magnification finder optical system of the present invention, respectively. 21
The figure is a schematic diagram showing the principal point position of the variable magnification finder optical system shown in FIGS. 19 and 20, and FIGS. 22 to 24 each show the variable magnification finder optical system according to the third embodiment of the present invention. Developed optical path diagrams at low, medium, and high magnifications, Figure 25~
FIG. 27 is a diagram of various aberrations at low magnification, medium magnification, and high magnification in the variable magnification finder optical system of the second embodiment of the present invention. In the figure, 1 is a focal plane, 2 is a condenser lens, 3 is a penta roof prism, 40 is an eyepiece, 10 is a first lens group, 20 is a second lens group, 30 is a third lens group, and 8 is an eye point. . Patent applicant: Canon Corporation Figure 1 Figure 2 Figure 3 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 16 Figure 18 Figure Q @ QX n(();.p)lI-point'”(o;
op) x a aberration C%) 19th
Figure 20 Figure 21 Figure Qin 22. . Heart 23 4゜ Height 24 [214゜ Island 25 Figure 26 Figure 27

Claims (4)

[Claims] (1) In a variable magnification finder optical system in which a viewfinder image formed on a focusing plate by a photographing lens is observed through a penta-roof prism with an eyepiece while changing the finder magnification, the eyepiece has at least two A first lens group having a positive focal length and having at least one negative lens, and a second lens group having a negative focal length having at least one negative lens, and at least one lens group in the first lens group. A variable magnification finder optical system characterized in that the finder magnification is made variable by moving the lens A and the second lens group in mutually opposite directions on the finder optical axis. (2) In a variable magnification finder optical system in which a viewfinder image formed on a focusing plate by a photographing lens is observed through a penta roof prism with an eyepiece while changing the finder magnification, the eyepiece lens is arranged in order from the penta roof prism side to at least two It is composed of a first lens group with a positive focal length having at least one positive lens, a second lens group having a negative focal length having at least one negative lens, and a third lens group having at least one positive lens. . A variable magnification finder optical system, characterized in that finder magnification is made variable by moving at least one lens A in the first lens group and the second lens group in opposite directions on the finder optical axis. (3) The variable magnification finder optical system according to claim 2, wherein the variable magnification finder optical system satisfies the following condition: f1<f3, where f1 is the focal length of the first lens group, and f3 is the focal length of the third lens group. . (4) The focal length of lens A in the first lens group is fA
3. The variable magnification finder optical system according to claim 2, wherein the variable magnification finder optical system satisfies the following condition: fA<f3, where f3 is the focal length of the third lens group.