JPH02309332A - Finder optical system with variable observation direction - Google Patents

Abstract

PURPOSE:To selectively and easily switch an eye level direction and a waist level direction by providing 1st and 2nd prisms having specified shapes and moving the 2nd prism in a direction perpendicular to an optical axis. CONSTITUTION:The transmission part of the incident surface 6a of the prism 6 is positioned on the optical axis in the case of eye level. At such a time, a luminous flux passing the prism 5 is transmitted through the transmission part of the incident surface 6a of the prism 6, projected from an injection sur face 6b and conducted to an ocular 7a. Then, an object image is observed from an eye point 8a in the eye level direction. In the case of waist level, the prism 6 is moved in the direction nearly perpendicular to the optical axis so that the reflection part of the incident surface 6a of the prism 6 is positioned on the optical axis. Thus, the luminous flux passing through the prism 5 is reflected on the reflection part of the incident surface 6a of the prism 6 and made inci dent on the prism 5 from the injection surface 5b again. The luminous flux is totally reflected on the incident surface 5a of the prism 5 and passes an injection surface 5c to be conducted to an ocular 7b. Then, the object image is observed from an eye point 8b in the waist level direction.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a finder optical system with variable observation direction, and in particular to a finder optical system that uses a plurality of prisms of a predetermined shape to capture an object image on a finder imaging plane formed by an objective lens. Finder optics with a variable viewing direction suitable for photographic cameras, video cameras, binoculars, etc. that allow switching between eye level and waist level directions. It is related to the system.

(Prior Art) Conventionally, for example, in the finder optical system of an eye-reflex camera, there has been a finder that selectively switches the viewing direction of a subject image to one of two directions: eye-level direction and waist-level direction. Various optical systems have been proposed.

For example, such a finder optical system capable of switching viewing directions has been proposed in Japanese Patent Laid-Open No. 51-39120.

Nos. 5(^) and 5(B) are schematic diagrams of the main parts of the finder optical system proposed in the same publication. The same figure (A) is when the viewfinder field of view is at eye level, the same figure (B)
) indicate waist level.

In the same figures (A) and (!), 51 is a fixed first prism, 52 is a rotatable second prism, and these two prisms 51 and 52 form an image on a viewfinder imaging plane (not shown). The image of the subject is corrected to an erect image.

53 is an eyepiece lens, 58a.

58b is each eye point.

In the same figures (^) and (B), by rotating the rotatable second prism 52 with the exit surface 51a and the entrance surface 52a facing each other according to the observation direction, the light flux from the 7JJ1 prism 51 is focused on the eye. The object image is observed by selectively switching to either the level direction ((8) in the same figure) or the waist level direction ((B) in the same figure).

However, in Figures (A) and (B), when switching the observation direction, since the second prism 52 is relatively large, a large storage space must be secured in advance for the rotation of the second prism 52. Therefore, the finder device as a whole tends to become larger and more expensive.

Furthermore, in Japanese Utility Model Publication No. 39-35290, the present applicant placed a removable reflection prism behind a so-called penta roof prism, and by inserting and removing the reflection prism, the observation direction can be changed between the eye level direction and the waist level direction. We are proposing a finder optical system that can be easily switched between two directions.

FIG. 6 is a schematic diagram of the main parts of the wJ, eastward variable finder optical system proposed in the same publication.

In the same figure, 64 is a penta roof prism for erected images;
Reference numeral 65 denotes a reflecting prism, which is disposed at the rear of the pentagonal roof prism 64 so as to be freely insertable and removable. 63a and 63b are eyepiece lenses, respectively, and 68a.

68b is each eye point.

In the figure, when the reflective prism 65 is retracted out of the finder optical path, the eyepiece lens 63a is used as an eye-level finder optical system, and the reflective prism 65
When inserted into the finder optical path, the eyepiece lens 63
b is used as a waist level finder optical system.

That is, at eye level (eye level finder optical, V
-) guides a luminous flux from an object (not shown) to an eyepiece lens 63a via a pentagonal roof prism 64, and observes the object image formed on the surface of a tip plate (not shown) from an eye point 68a, that is, from the eye level direction. are doing.

Furthermore, during waist level observation (waist level finder optical system), the reflective prism 65, which had been retracted outside the finder optical path, is inserted into the optical path behind the penta roof prism 64, as shown in the figure. Then, the light beam from the object (not shown) is guided to the eyepiece lens 63b via the penta-roof prism 64 and the reflection prism 65, and the object image formed on the surface of the focusing plate (not shown) is focused on the eye point 63.
The image is observed from b, that is, from the waist level direction.

However, in the viewfinder optical system with variable observation direction proposed in the same publication, the removable reflection prism 65 is relatively large, so a large storage space must be secured in advance for insertion and removal. Similarly, there was a tendency for finder devices as a whole to become larger.

(Problems to be Solved by the Invention) In order to solve the problems shown in the conventional example, the present invention aims to solve the problems shown in the conventional example. By efficiently arranging the two prisms of the second prism and selectively moving the second prism in a direction substantially perpendicular to the optical axis depending on the viewing direction of the subject image, two It is an object of the present invention to provide a relatively compact and inexpensive finder optical system capable of variable observation direction, which can selectively and easily change one of the directions.

(Means for solving the problem) A finder optical system having an objective lens and at least two different observation directions for observing a subject image formed by the objective lens, the finder optical system having at least two different observation directions, the objective lens and an observer A first prism and a second prism are arranged between them in order from the subject side, and the first prism has an entrance surface (5a) that is substantially perpendicular to the optical axis and a first exit surface (5a) that is inclined with respect to the optical axis.
b), and a second exit surface (5c) substantially orthogonal to the first exit surface (5b), and the second prism is opposite to the first exit surface (5b) of the first prism. The entrance surface (6a) is tilted with respect to the optical axis, and the exit surface (6a) is approximately perpendicular to the optical axis.
6b), and the entrance surface (6a
) has at least two regions, a transmissive part and a reflective part, and the second prism moves in a direction substantially perpendicular to the optical axis so that one of the transmissive part and the reflective part is located on the optical axis. Note: The observation direction of the object image formed by the objective lens is switched using the light beam passing through or reflecting through the transmitting section and the reflecting section.

(Embodiment) FIG. 1 is a schematic diagram of a main part of an embodiment of a photographing system when the present invention is applied to a single-lens reflex camera using a pentagonal roof prism. In the same figure, 9 is a luminous flux from an unillustrated subject;
1 is an objective lens, 2 is a quick return mirror, and 2
A light beam 9 from the objective lens 1 is reflected upward where a focusing plate 3, which will be described later, is arranged. Reference numeral 3 denotes a focusing plate, on which a subject image is formed by the objective lens 1. 4 is a penta roof prism, which corrects the subject image formed on the focusing plate 3 into an erect image.

5 and 6 are a first prism and a second prism, respectively, according to the present invention.

The first prism 5 is provided behind the pentagonal roof prism 4, and has an entrance surface 5a that is substantially perpendicular to the optical axis, a first exit surface 5b that is inclined with respect to the optical axis, and an entrance surface that is approximately orthogonal to the first exit surface 5b. It has a second exit surface 5c.

The second prism 6 is provided behind the first exit point 5b of the first prism 5.
It has an entrance surface 6a that is inclined with respect to the optical axis and an exit surface 6b that is substantially perpendicular to the optical axis.

Further, the incident surface 6a is divided into at least two regions, a transmitting section and a reflecting section, as shown in FIG. 2(B), which will be described later.

Further, the second prism 6 is configured to move approximately perpendicularly to the optical axis by 11 so that either one of the transmitting part and the reflecting part provided on the incident surface 6a is located on the optical axis. It is located.

7a and 7b are eyepiece lenses, and 8a and 8b are eye points.

Next, the shapes of the first prism 5 and the second prism 6, which are characteristics of the present invention, and their optical effects will be explained using FIGS. 2 and 3.

FIG. 2 (A) is a perspective view of the first prism 5. FIG. 2 (B)
is': a perspective view of the fi2 prism 6, No. 3 (A).

(It) is an explanatory diagram showing how to switch the observation direction, and FIG. 3(A) is at eye level (eye level finder optical system), and FIG. 3(B) is at waist level (waist level finder optical system). (system) is shown.

As shown in FIG. 2(A), the first prism 5 has an entrance surface 5a that is substantially perpendicular to the optical axis, and a first exit surface 5b that is inclined to the optical axis.
and a second exit surface 5 substantially orthogonal to the first exit surface 5b.
It has c.

As shown in FIG. 2(B), the second prism 6 has an entrance surface 6a tilted relative to the first exit surface 5b of the first prism 5 and an exit surface 6b substantially perpendicular to the optical axis. have.

Of these, the incident surface 6a is divided into two regions: a transmitting section 6al and a reflecting section 6a2 coated with a reflective film made of, for example, aluminum.

In this embodiment, by using two prisms having such a shape, when used as an eye level finder optical system, the transmitting part 6al is positioned on the optical axis 101 as shown in FIG. 3(A). I have to. At this time, the first
The light beam passing through the prism 5 enters the incident surface 6 of the second prism 6.
The light passes through the transparent portion 6al of a, exits from the exit surface 6b, and enters an eyepiece (not shown).

In addition, when using it as a waist level finder optical system, from the state shown in Fig. 3(A), move the reflecting part 6 as shown by arrow A.
The second prism 6 is moved in a direction substantially perpendicular to the optical axis 101 so that a2 is located on the optical axis 101. (Situation in FIG. 3(B)) At this time, as shown in FIG. 3(B), the light beam that has passed through the first prism 5 is reflected upward by the reflecting portion 6a2 of the incident surface 6a of the second prism 6, and is again The light is incident on the first prism 5. The light beam incident from the first exit point 5b of the first prism 5 is transmitted to the entrance surface 5a of the first prism 5.
The light is totally reflected by the light beam, exits from the second exit surface 5c, enters an eyepiece (not shown), and becomes i/.

Next, the observation state of the subject image of the finder optical system in this embodiment will be described.

In this embodiment, a light beam 9 from an object (not shown) passes through the objective lens 1, is reflected upward by the quick return mirror 2, is guided onto the surface of the focusing plate 3, and forms an image of the object on that surface. The diffused light beam from the focusing plate 3 enters the first prism 5 via the pentagonal roof prism 4.

At eye level (eye level finder optical system)
The transmitting portion of the entrance surface 6a of the second prism 6 is positioned on the optical axis. At this time, the luminous flux that has passed through the first prism 5 passes through the transmitting portion of the entrance surface 6a of the second prism 6, emerges from the exit surface 6b, and is guided to the eyepiece lens 7a. From the eye point 8a, the subject image is observed on the focus plate 3 from the eye level direction.

Next, at waist level (waist level finder optical system), the second prism 6 is moved in a direction substantially perpendicular to the optical axis so that the reflective part of the entrance surface 6a of the second prism 6 is located on the optical axis. . As a result, the light beam that has passed through the first prism 5 is reflected upward at the reflection part of the entrance surface 6a of the second prism 6 as shown by the dotted line in the same figure, and is again 7gl on the exit surface 5.
The light enters the first prism 5 from b. And the luminous flux is the first
The light is totally reflected by the entrance surface 5a of the prism 5, passes through the second exit point 5c, and is guided to the eyepiece lens 7b. The subject image on the three focusing plates is observed from the eye point 8b from the waist level direction.

In this embodiment, the entrance surface 6a of the second prism 6 is divided into two areas, a transmission part and a reflection part, and either the transmission part or the reflection part is located on the optical axis depending on the observation direction. The second prism 6 is moved in a direction substantially perpendicular to the optical axis.

Thereby, the observation direction can be selectively and easily switched to either the eye level direction or the waist level direction to observe the subject image.

Next, the first example according to this embodiment. The conditions that define the shapes of the second prisms 5 and 6 will be explained.

If the angle between the normal line of the first prism 5 and the optical axis is θ, then the angle θ means that the entire finder luminous flux (assuming an opening angle of about ±10°) Surface 5b
For example, the first
When the refractive index of the material of the prism 5 is n, 5 inches (θ+10°) < 1 / n = (1)
must be satisfied.

On the other hand, when the entrance surface 5a of the first prism 5 is made perpendicular to the optical axis, the above-mentioned conditional expression (1) is satisfied, and the light is reflected by the reflection part 6a2 of the entrance surface '6a of the second prism 6. 1st
It is necessary to set it so that the light flux that has re-entered the prism 5 is totally reflected at the entrance surface 5a of the first prism 5.

At this time, the width of the incident angle of the light beam with respect to the normal to the entrance surface 5a of the first prism 5 is 2θ±10', so in order for the entire finder light beam to be totally reflected at the entrance surface 5a of the first prism 5, 5in (2θ-10°)≧1/n (
2) must satisfy the following formula.

Furthermore, unless the entrance surface 6a of the second prism 6 is set to face the first exit surface 5b of the first prism 5, the first. Second
The wedge-shaped air gap between the prisms 5 and 6 causes color dispersion, which is undesirable.

Therefore, in this embodiment, the angle of the normal to the incident mj6a of the second prism 6 with respect to the optical axis is equal to the angle θ between the normal to the exit surface 5b of the first prism 5 and the optical axis in conditional expression (1) above. It is stipulated that they almost match.

That is, the entrance surface 6a of the second prism 6 is set to face the first Q# exit surface 5b of the first prism 5, that is, to be substantially parallel to it.

In this way, in this embodiment, the first. By specifying and arranging the shape of the second prism 5.6 so as to satisfy conditional expressions (1) and (2), the luminous flux from the subject can be efficiently transferred to the eye-level eyepiece or the waist-level eyepiece. Each light is guided to the eyepiece.

In this embodiment, since the movable second prism 6 is relatively small, the entire device can be easily miniaturized, and a compact viewfinder optical system with variable observation direction can be achieved.

Also, 1st. If the second prism 5.6 is molded from a material such as resin, it has the advantage that it can be manufactured at an extremely low cost and costs can be reduced.

FIG. 4 is a schematic diagram of main parts of another embodiment when the present invention is applied to a finder optical system of a lens shutter camera or the like.

In this figure, the same elements as those shown in FIG. 1 are given the same reference numerals. Note that 11 is an objective lens of a finder system.

In this embodiment, a light beam from an object (not shown) is diverged by the objective lens 11 and enters the first prism 5. At eye level, the transmitting portion of the entrance surface 6a of the second prism 6 is positioned on the optical axis. The light beam from the objective lens 11 that has passed through the first prism 5 is transmitted through the transmission portion of the entrance surface 6a of the second prism 6 and guided to the eyepiece lens 7a. This allows the subject image to be observed from the eye level.

Next, at waist level, the entrance surface 6a of the second prism 6
The second prism 6 is arranged such that the reflecting part of the second prism 6
is moved in a direction substantially perpendicular to the optical axis. As a result, the light beam from the objective lens [1] that has passed through the first prism 5 is reflected upward by the reflection portion of the entrance surface 6a of the second prism 6, and is made to enter the first prism 5 again. The light beam is totally reflected by the entrance surface 5a of the 7P, 1 prism 5, and then guided to the eyepiece lens 7b. This allows the subject image to be observed from the waist level direction.

In this way, in this example, objective lens 1! and the observer, the first . A second prism 5.6 is arranged, and the transmission part and reflection part provided on the entrance surface 6a of the second prism 6 are switched and used so that the transmission part is located on the optical axis at eye level, and at waist level. The second prism 6 is moved in a direction substantially perpendicular to the optical axis so that the reflecting portion is located on the optical axis. As a result, the subject image is observed by selectively switching the light flux from the subject to either the eye level direction or the waist level direction.

In addition to the embodiments described above, the present invention can be widely applied to various finder optical systems (observation optical systems) such as real-image finder optical systems of video cameras and the like, binoculars, and the like.

Further, in the embodiments described so far, the first and second prisms are arranged between the objective lens and the eyepiece, but the invention is not limited to this, and as shown in FIG. The first and second prisms may be arranged.

That is, as shown in FIG. 7, an eyepiece lens 7c is arranged behind the Bentatahab prism 4, and a first prism 5 and a second prism 6 are arranged behind it, and the light after passing through the eyepiece lens 7c is The light beam can also be divided into the eye level direction and the waist level direction by the first prism 5 and the second prism 6. According to this method, only one eyepiece lens is required and can be manufactured at low cost.

(Effects of the Invention) According to the present invention, the first lens having a predetermined shape is disposed between the objective lens and the observer. The second prism is arranged efficiently, and the entrance surface of the second prism is divided into two Jti regions, the transmission section and the reflection section, depending on the observation direction. By configuring the second prism to be moved in a direction substantially perpendicular to the optical axis so that one of the two prisms is located on the optical axis, the entire device can be made compact, and it is also inexpensive and simple. Depending on the configuration, it is possible to achieve a finder optical system with four observation directions, which can selectively observe a subject image in either the eye-level direction or the waist-level direction.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the main part of an embodiment of an m-shade system when the present invention is applied to a single-lens reflex camera using a penta roof prism, and FIG. 1. An explanatory diagram of the second prism, Figures 3 (^) and (B) are explanatory diagrams showing the method of switching the observation direction in the present invention, and Figure 4 is an explanatory diagram of the present invention applied to the finder optical system of a lens shutter camera. FIG. 5 (A
), (B), FIG. 6 is a schematic diagram of the main part of a conventional finder optical system, and FIG. 7 is a schematic diagram of the main part of another embodiment of the present invention. In the figure, 1.11 is an objective lens, 2 is a quick return mirror, 3 is a focusing plate, 4 is a penta roof prism, 5 is a first prism, 5a is an entrance surface, 5b is a first exit surface, 5c is a second exit surface , 6 is the second prism, 6a is the incident surface, 6a1
is a transmission part, 6a2 is a reflection part, 6b is an exit surface, 7a, 7b
is an eyepiece, 8a and 8b are eye points, and 9 is a luminous flux. Patent applicant Canon Co., Ltd. 1; 7'7 1 mouth b Fig. 2 1--Y--- d'\-no' Mo 5 Fig. (A) (B)

Claims (1)

[Claims] (1) A finder optical system having at least two different observation directions for observing an objective lens and a subject image formed by the objective lens, and between the objective lens and the observer, 1st prism and 2nd prism
A prism is arranged, and the first prism has an entrance surface (5a) substantially perpendicular to the optical axis, a first exit surface (5b) tilted to the optical axis, and a first exit surface (5b) with respect to the first exit surface (5b). The second prism has a second exit surface (5c) that is substantially perpendicular to the first exit surface (5c), and the second prism has an entrance surface (6a) that is inclined with respect to the optical axis relative to the first exit surface (5b) of the first prism. The second prism has an exit surface (6b) substantially perpendicular to the optical axis, and the entrance surface (6a) of the second prism has at least two areas, a transmitting part and a reflecting part. The transmitting part and the reflecting part are arranged so that either one is located on the optical axis and can be moved in a direction substantially perpendicular to the optical axis, and the light beam passing through or reflecting through the transmitting part and the reflecting part is 1. A finder optical system with variable viewing direction, characterized in that the viewing direction of a subject image formed by the objective lens is switched using the following.