JPH01319724A - Variable power finder optical system - Google Patents

Abstract

PURPOSE:To vary a finder magnification and eye point by a simple means with compact constitution by constituting an eyepiece lens of 3 lens groups and moving the 2nd lens group on the optical axis to execute variable power. CONSTITUTION:The eyepiece lens 40 is made of 3-group 3-element constitution consisting of the 1st lens group 10 which is a positive single lens, the 2nd lens group 20 which is a negative single lens and the 3rd lens group 30 which is a positive single lens. The 1st lens group 10 and the 3rd lens group 30 are fixed and the 2nd lens group 20 is moved from the 1st lens group 10 toward the 3rd lens group 30 to change the low magnification to a high magnification so that the image is formed on a focal plate 1 by an eye point 8 and is observed. The refracting power of the entire part can be increased by increasing the spacing between the 1st lens group and the 2nd lens groups which are different in the code of the focal length. 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 has 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 and observe the field of view.

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 has the drawback that it requires a place for the lens to retreat, resulting in space problems and making it impossible to make the entire device 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 eyepoint, the method of attaching an attachment lens behind the eyepiece lens would result in poor operability due to the lens being a separate component, and would make it difficult to make the entire device more compact. There is a drawback that there is no such thing.

(Problems to be Solved by the Invention) The present invention provides a method for moving one lens group constituting the eyepiece on the optical axis of the finder when observing a finder image with an eyepiece placed behind the exit surface of a penta roof prism. The objective of the present invention is to provide a variable magnification finder optical system with a compact and simple configuration that allows the finder magnification and eye point to be varied while keeping the finder diopter constant with simple operation, and maintains good optical performance as the magnification changes. purpose.

(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 In order from the penta roof prism side, there is a first lens group having 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 at least one positive lens. It is composed of a third lens group having a positive focal length, and the finder magnification is made variable by moving the second lens group 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 a single lens 4 with positive refractive power, the second lens group 20 is composed of a single lens 5 with negative refractive power, and the third lens group 30 is composed of a single lens 5 with positive refractive power. It is composed of a lens 6. 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 one positive lens and a second lens group 10 consisting of one negative lens.
Third lens group 3 consisting of lens group 20 and one positive lens
It is composed of three lenses in three groups, with the first lens group 10 and the third lens group 10.
The lens group 30 is fixed, and the second lens group 20 is moved from the first lens group 10 side to the third lens group 30 side on the viewfinder optical axis to change the finder magnification from low magnification to high magnification at eye point 8. A 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 and satisfactorily correcting fluctuations 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 64.2 mm at low magnification in Figure 1, 60.5 mm at medium magnification in Figure 2, and 57.0 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 0.78 times, 0.83 times, and 0.88 times, respectively.

Also, the focal point mfif of the first lens group 10 of the eyepiece 40
+ is f, = 44.0 mm, focal pressure s of the second lens group 20
f2 is f2==-70,0mm, 3rd lens group 30
The focal pressure @13 is f3=163.4mn+.

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 an eyepiece;
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 second lens group 20A is positioned at the eye point 8 on the finder optical axis.
The magnification is changed from low to high magnification by moving the lens in the direction.

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・φΔ+φB−e・φA・φB...
・(1) φW-φA+ φB-(e+Δe)φA-φB
--- It is expressed as (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' on focus plane 1 is D.
, the following equation holds true when the refractive power of the eyepiece is φ.

The finder diopter is expressed in -1000/D diopters. (However, D shall be expressed in units of +nm.) 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 11ID is D=1000 mm, 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 w from the focal plane l to the front principal point position increases as the refractive power φ of the eyepiece increases.
This means that iL 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 as follows.

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 φB<0,
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 structure of the eyepiece 40A is, in order from the penta-roof prism side, 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. It has a three-group configuration, and when changing the magnification, the second
By moving the lens group on the viewfinder optical axis, a variable magnification finder optical system is achieved in which the viewfinder magnification can be varied while keeping the viewfinder diopter constant.

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 length mf of the entire variable magnification finder optical system.

To give a specific example, in Fig. 1, f = 64.2 mm, L = 60
．． 2mm, f=60.5mo+, L=56.
8mm, f=57.0mm in Figure 3.

Changes in the finder diopter are prevented by setting L=53.7+nm.

In this embodiment, in order to easily change the viewfinder magnification, the following condition is satisfied: fl < f3, where the focal length of the first lens group 10 is fl and the focal length of the third lens group 30 is f3. It's good to let it happen.

By arranging a fixed third lens group with a positive focal length that satisfies this condition, it is possible to easily change the viewfinder magnification while preventing changes in the viewfinder diopter, and also to avoid the occurrence of various aberrations, especially in the first lens group. Various aberrations generated by the convex lenses in the lens group are reduced.

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.

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

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 one positive lens and one negative lens. It is composed of three 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 second lens group constituting the eyepiece on the finder optical axis, and the pentagonal roof prism is effectively used as shown in FIGS. 10 to 12. By utilizing
The finder magnification is increased to provide a finder image that is easy to see for an observer who wants 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 given 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 one positive lens and a second lens group 10 consisting of one negative lens.
Third lens group 3 consisting of lens group 20 and one positive lens
It consists of 3 elements in 3 groups of 0. When changing the magnification,
The lens group 20 is moved from the first lens group 10 side to the third lens group 30 side on the finder optical axis to change the finder magnification from low magnification to high magnification, and at eye point 8, the focusing plate is set using a photographing lens (not shown). I am observing the finder image formed on 1.

In this embodiment, a fixed third lens group is arranged to reduce fluctuations in aberrations during zooming, satisfactorily correct various aberrations, and obtain a finder image with high optical performance.

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.

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.
63.4no+ at low magnification in Figure 3, 60.1mm at medium magnification in Figure 14, 57.0 at high magnification in Figure 15
mm, and for example, as a photographic lens, the focal length is 50 m.
When a standard M lens is attached, the viewfinder magnification is approximately 0.79x, 0.83x, and 0.88x, respectively.

In this embodiment, the focal ratio fat t of the first lens group of the eyepiece 40 is f , = 41, 3 non, and the focal ratio * t 2 of the second lens group is f 2 = -60, 0
mm, the focal length f3 of the third lens group is f3=144.7
cnm.

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 ratio llf of the entire variable magnification sounder optical system, the distance from the focal plane to the front principal point of the variable magnification finder optical system is shortened.

Specifically, in Fig. 13, f=63.4mm, L
= 59, 6 mm, f = 60.1n in Fig. 14
on%L = 56, 7 mm, 15th, f = in the figure
57. Omn+, L = 54, 0 mm, thereby preventing changes in the finder diopter.

In this embodiment, in order to easily change the viewfinder magnification, the following condition is satisfied: fl < f3, where the focal length of the first lens group 10 is fl, and the focal length of the third lens group 30 is f3. It's good to let it happen.

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.

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. In the second embodiment, the optical path diagram and aberration diagram show that the distance between the focal plane 1 and the condenser lens 2 is 0.5.
mm, and the distance between the eyepiece 40 and the eye point 8 is 16.
It is drawn as 0mm.

Numerical Example 1 1 (1=loo DI= 5.2 N
I-1,49171v 1-57.4R2--65,0
0D 2- 1.2 R3=oo D 3-80. ON 2-1.5
1633 v 2-64.11 (4-cc+
D4-2.0 R5-60,72D 5-6.0 N 3-1
．． 8:]400 ν3-37.2R6--88,7
606-Variable R7--59,18D 7- 1.5 N 4-
1.80518 ν4-25.4R8-1194,
11D 8- Variable R9 Heavy 84.35 D 9- 2.5 N 5
-1.51633 υ5-64. IRIO-Cx) Numerical Example 2 Rh oo D 1- 5.2 N 1-
1.49171 v I-57,4R2--65,
00D 2- 1.2 R3-oo D 3-80.0 N 2-1
．． 51633 v 2-64.1R4-■ D4
-2.0 R5-59, 34D 5-6. ON 3=1.834
00 v 3-37.2R6--78,29D 6
- Variable R7--57, 11D 7- 1.5 N 4-
1.80518 ν4-25.4R8-316,9
5D 8- Variable R9-74, 73D 9- 2.5 85-1.5
1633 ν5-64. IRIO-■ (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 group having a positive refractive power. By moving the second lens group on the viewfinder optical axis to change the magnification, the viewfinder magnification and eye point can be made variable with a compact structure and simple means. It maintains good optical performance due to magnification, and is also good for observers who want to observe only the subject image at high magnification, and also for observers who use glasses etc. and want to shift their eye point backwards. It is possible to achieve a variable magnification finder optical system with a simple configuration that allows observation of a finder image.

[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
This figure is a schematic diagram showing the principal point position of the variable magnification finder optical system shown in FIGS. 19 and 20. 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. . Figure 1 Figure 2 Figure A Convex Figure 3 Figure O 0 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure An Figure 15 An Figure 19 Figure 20

Claims (2)

[Claims] (1) 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 lens is arranged in order from the penta roof prism side to at least one a first lens group of positive focal length having at least one positive lens; a second lens group of negative focal length having at least one negative lens; and a third lens group of positive focal length having at least one positive lens. A variable magnification finder optical system comprising a lens group, characterized in that the finder magnification is made variable by moving the second lens group on the finder optical axis. (2) The variable magnification finder optical system according to claim 1, 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. .