JPH0524908Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Technical field The present invention relates to a roof prism for a camera lens. More specifically, the invention relates to a roof prism for a camera lens. More specifically, the invention relates to a roof prism for a camera lens. When the optical path switching mirror is placed in a position to guide the light emitted from the photographing lens to the viewfinder side, the object image formed on the viewfinder screen disposed at the rear of the optical path is corrected through the optical path switching mirrors. This invention relates to a roof prism for a camera viewfinder that is used as an observation image of an erect image.

(b) Prior art The finder optical system in a single-lens reflex camera bends an inverted, left-right reversed subject image incident on the film side from the photographic lens upward via a quick return mirror, creating a finder screen. After forming an image on the subject, a pentagonal roof prism is used to obtain an erect image of the subject (erect image) with the left and right sides rotated in the normal direction.

However, in such cameras,
Since a pentagonal roof prism is used to convert a subject image whose left and right sides have been reversed into a subject image whose right and left sides have been rotated in the normal direction, a problem arises in that the size of the camera becomes bulky.

However, it is also conceivable to place two mirrors above the front winder screen without using a pentagonal roof prism to convert the left-right reversed subject image into an erect, normal observation image. Although this method solves the problem of bulkiness mentioned above, the distance to the eyepiece (optical path length) becomes shorter, so the magnification of the viewfinder must be increased, and along with this, the eyepiece Since the lens also becomes larger, the above-mentioned problems cannot be completely solved.

By the way, there is a finder optical system for a single-lens reflex camera described in Japanese Patent Publication No. 45212/1983 (hereinafter referred to as "first conventional example"), which was developed in view of the drawbacks of the pentagonal roof prism.

This first conventional finder optical system has a prism installed above the focal plane of a single-lens reflex camera, and an erected inverted image of the focal plane enters from the entrance plane and is reflected forward at the first reflective surface. After total reflection on the incident surface, it is reflected backward on the second reflection surface, and exits from the exit surface to form an inverted inverted image.The relay lens forms an erect normal image on the second focal plane, and the eyepiece lens It is designed to be observed.

However, when configured as in this first conventional example, the image obtained by the prism is an inverted inverted image, and a relay lens and an eyepiece lens are required to convert this into an erect normal image. As the configuration becomes more complex and costs inevitably rise,
Moreover, the size of the viewfinder in the front-rear direction becomes large, resulting in a drawback that miniaturization of the camera is hindered.

On the other hand, as another work that took into account the shortcomings of the pentagonal roof prism,
There is a finder prism for a reflex camera described in Japanese Patent Publication No. 2003-110002 (hereinafter referred to as "second conventional example").

The second conventional finder prism has an entrance surface located horizontally, an optical axis ray that is located above the entrance surface, and is inclined at a predetermined angle from the optical axis ray that enters from the entrance surface. In order to completely reflect the oblique rays at the incident surface, a first reflecting surface is set at an angle to the incident surface so as to reflect these rays obliquely backward and downward, and a first reflecting surface is positioned obliquely upward and backward from the incident surface. , a roof surface whose angle with respect to the horizontal plane is set so that all of the light rays totally reflected on the incident surface are totally reflected diagonally downward, and a roof surface located below this roof surface that reflects all the light rays from the roof surface. It consists of a third reflecting surface set at an angle with respect to the horizontal plane so as to cause total reflection backwards, and an exit surface located perpendicularly behind the third reflecting surface, and this exit surface is located above the entrance surface. It is characterized by

However, in the case of the second conventional example of the finer prism having such a configuration, since all of the above-mentioned reflecting surfaces reflect the light rays diagonally backward, the length of the finer prism in the front and rear direction becomes large. This hinders the miniaturization of cameras, and when trying to miniaturize cameras, the eyepiece of the viewfinder protrudes greatly behind the camera body, which is not only inconvenient for use, but also extremely inconvenient for storage and portability. It is. In particular, since the prism has a complicated shape with a curved shape,
A third prism consisting of a first prism forming an entrance surface and a first reflecting surface, a second prism forming a roof surface, and a third prism forming a third reflecting surface and an exit surface.
It is necessary to manufacture two prisms by bonding them together.
The disadvantage is that the manufacturing cost increases significantly.

(c) Purpose The present invention was developed in view of the above-mentioned circumstances, and its purpose is to provide a camera with a simple structure, low cost, and light weight without causing any inconvenience in use. To provide a roof prism for a camera viewfinder, in which the upper dimension of the screen and the dimension in the front and back direction of the camera can be shortened, and in particular, the exit surface of the roof prism can be accommodated within the camera, and the protrusion of the eyepiece part of the viewfinder can be extremely reduced. .

(d) Configuration In order to achieve the above-mentioned object, the present invention provides optical path switching via a photographic lens and an optical path switching mirror that sequentially switches the light emitted from the photographic lens into a position where it guides it to the film surface and a position where it guides it to the viewfinder side. For a camera viewfinder in which the subject image formed on a viewfinder screen disposed at the rear of the optical path when the mirror is positioned to guide the light emitted from the photographing lens toward the viewfinder side is an erect normal observation image. In a roof prism, a critical angle is formed between a first surface through which a beam of light passing through a fine dust screen on which a subject image is formed is incident and the first surface through which the beam passes through, and the first surface which receives the transmitted beam. a second surface that reflects diagonally forward so as to be incident again at an incident angle exceeding the second surface; a third surface made of a roof surface that receives the totally reflected light beam and reflects it diagonally backward so that it is incident on the first surface again at an incident angle exceeding the critical angle; and a fourth surface that emits the light beam that has been reflected and further totally reflected by the first surface, and these first to fourth surfaces are integrally formed on the surface of one prism. It is characterized by the presence of

Embodiments of the present invention will be described below with reference to FIGS. 1 to 3.

First, a first embodiment, which is the basis of the present invention, will be described with reference to FIG.

A mirror 20 for optical path switching is arranged at an angle of 45 degrees behind a photographing lens 10 provided on the camera body, and a film 30 is positioned behind this mirror 20.

The photographing lens 10 is constituted by an erecting normal image optical system in which a converging light transmitting element called a self-focusing element whose refractive index changes radially in the radial direction is provided in the optical system. Further, a finder screen (so-called focusing plate) 40 is disposed above the mirror 20 at a position conjugate with the film 30. A subject image is formed on this finder screen 40 after the light beam from the photographing lens 10 is bent upward by a mirror 20. A prism 50 for use is provided.

The longitudinal section of this prism 50 has a pentagonal shape,
Its bottom surface is formed parallel to the surface of the finder screen 40, and serves as a first surface 51 onto which the light flux transmitted through the finder screen 40 is incident. Further, above the first surface 51, a second surface 52 that has a mirror finish is formed. This second surface 52 reflects the luminous flux P ₁ that passes through the first surface 51 and converts it into a luminous flux P ₂ . When the light beam P ₂ enters the first surface 51 again, the angle of incidence θ with respect to the first surface is equal to or greater than the angle θ=sin ^-1 (1/n) (where n: refractive index)...(1) The relationship between the first surface 51 and the second surface 52 is set so that the angle is greater than or equal to the critical angle.

That is, the angle θ ₂ formed by the first surface 51 and the second surface 52 is the angle at which the light beam is finally imaged, that is, the angle of the light beam emitted from the fourth surface 54 which is the exit surface of the prism 50. Assuming that the angle is 2θ ₁ , it is sufficient to set it so that θ ₂ =(θ+θ ₁ )/2 (2) or more.

The first surface 51 and the second surface 51 have such an angular relationship.
In front of the surface 52 (on the subject side), there is a first surface 51
A third surface 53 is formed which has a reflective surface that reflects the luminous flux P ₃ totally reflected by the light beam P 3 toward the rear.

Further, a third surface 53 is provided at the rear of the prism 50.
The luminous flux P ₄ reflected by is emitted to the rear (transmission)
A fourth surface 54 is formed. An eyepiece lens 55 is disposed behind this fourth surface 54.

In this embodiment configured in this way, the light beam P ₀ refracted by the photographing lens 10 is directed to the mirror 20
is in a position to guide the light flux P ₀ to the viewfinder side, it is bent upward by the mirror 20,
An image is formed on the viewfinder screen 40.

The light flux transmitted through the finder screen 40 at this time is incident on the first surface 51 of the prism 50 and becomes a light flux _P1 . This luminous flux P ₁ is reflected by the second surface 52 and becomes the luminous flux P ₂ reflected by the first surface 51.
It is incident again at an incident angle θ exceeding the critical angle, and is totally reflected on the same surface to become a luminous flux P ₃ . This luminous flux P ₃ is the third
is reflected by the surface 53 to become a luminous flux P ₄ , and this luminous flux P ₄ is further emitted from the fourth surface 54,
The luminous flux becomes _P5 . This luminous flux P ₅ is magnified and imaged by the eyepiece 55, and as a result, an erect, normal image (an observation image in which the left and right sides are rotated in the normal direction) can be observed behind the eyepiece 55. .

Note that 56 is a cut groove for cutting out ghost light.

According to the first embodiment constructed and operated in this way, there is no need to form a roof surface for inverting the left and right images, so the processing of the prism 50 is facilitated, and the manufacturing cost can be reduced compared to that of the conventional pentagonal prism. This can be significantly reduced compared to a roof prism.

Moreover, this prism 50 does not have a roof surface, and since the first surface 51, which is the surface on which the imaging light on the finer screen 40 is incident, is also used as a reflective surface for the finer beam, the second surface Although the inclination angle θ ₂ of the prism 52 is subject to the restriction of the above equation (2), the height can be made lower than that of the pentagonal roof prism. Therefore, a single-lens reflex camera to which this prism is applied can reduce the overall height.

Next, a second embodiment, which is the basis of the present invention, will be described with reference to FIG.

In FIG. 2, the prism 60 disposed above the finder screen 40 has a pentagonal vertical cross section, and its bottom surface is a first surface 61 on which the light flux transmitted through the finder screen 40 is incident. It's getting old. Above and in front of this first surface 61, a second surface 62 and a third surface 63, which are mirror surfaces, are formed, respectively.

The difference between the prism 60 in the second embodiment and the prism 50 in the first embodiment described above is that the luminous flux P ₂ reflected on the second surface 62 is
Instead of reflecting on the surface 51 of the third surface 63
The luminous flux reflected by this third surface 63
The point where P ₆ is reflected by the first surface 61 and the point where P 6 is reflected by the first surface 61
When the luminous flux P ₇ reflected on the surface 61 of the prism 60 is emitted from the fourth surface 64 to the rear of the prism 60 to become a luminous flux P ₈ , the emitting direction of the luminous flux P ₈ is the same as that of the prism 50 described above. The point is that it is not substantially parallel to the optical axis of the lens, but is oriented obliquely upward.

Here, the luminous flux reflected by the third surface 63
The condition for total reflection of P ₆ by the first surface 61, which is originally a transmitting surface, is that the incident angle θ of the luminous flux P ₆ is equal to or greater than the angle obtained by the above equation (1), as described above. , and the angle θ ₂₃ between the second surface 62 and the third surface 63 may be set to satisfy the following equation.

θ ₂₃ <(π/2)−(θ+θ ₁ )/2 (3) To explain the operation of the second embodiment configured in this way, the luminous flux P ₀ emitted from the photographing lens 10
is bent upward by approximately 90° by the mirror 20,
An image is formed on the viewfinder screen 40. This luminous flux P ₀ becomes a luminous flux P ₁ incident on the first surface 61 and is reflected by the second surface 62 to become a luminous flux P ₂ . Further, this luminous flux P ₂ is reflected by the third surface 63 and is incident on the first surface 61 as a luminous flux P ₆ at an incident angle of θ. At this time, the incident angle θ
is the total internal reflection condition as shown in equation (1) above, that is,
Since the incident angle θ satisfies the condition that the incident angle is greater than or equal to the critical angle, the light is totally reflected by the first surface 61 and becomes a luminous flux P ₇ .
This luminous flux P ₇ is emitted from the fourth surface 64 as a luminous flux P ₈ to the eyepiece 55 side.
The image is formed by 5. As a result, the photographer (user) can observe the virtual image of the erect image magnified by the eyepiece 55.

In the case of the second embodiment, the height of the prism is slightly increased compared to the first embodiment, but the total height can be made lower than that of the pentagonal roof prism, and substantially the same effect as the first embodiment can be obtained. It will be done.

By the way, in the case of a camera equipped with a normal photographing lens that is not an erecting normal image optical system, if the prisms 50 and 60 of the first and second embodiments are applied as they are, the left and right images will become inverted.
The present invention has been devised to deal with this problem.

FIG. 3 is a sectional view showing a schematic configuration of a single-lens reflex camera using the roof prism for camera viewfinder according to the present invention.

In FIG. 3, the photographic lens 10' provided on the camera body is not an erect normal image optical system as shown in FIGS. 1 and 2, but is a normal inverted reverse image optical system.

Behind such a photographic lens 10', there is a first lens.
Similar to what is shown in FIGS. 2 and 2, a mirror 20 for optical path switching is arranged at an angle of 45 degrees, and a film 30 is positioned behind this mirror 20. Further, a finder screen (so-called focusing plate) 40 is disposed above the mirror 20 at a position conjugate with the film 30.
A subject image is formed on this finder screen 40 after the light beam from the photographing lens 10' is bent upward by a mirror 20. A roof prism 70 for inder is provided.

The roof prism 70 has a pentagonal vertical cross section, and the bottom surface of the roof prism 70 has a pentagonal shape.
A first surface 5 that is formed parallel to the surface of
It's becoming 1. Further, above the first surface 51, a second surface 52 that has a mirror finish is formed. This second surface 52 reflects the luminous flux P ₁ that passes through the first surface 51 and converts it into a luminous flux P ₂ . As described above, when the light beam P ₂ enters the first surface 51 again, the angle of incidence θ with respect to the first surface 51 is set to be equal to or greater than the angle obtained by the above equation (1), that is, the critical angle The first
The relationship between the surface 51 and the second surface 52 is set.

That is, as described above, the angle θ ₂ formed by the first surface 51 and the second surface 52 is the angle at which the light beam is finally focused, that is, from the fourth surface 54 which is the exit surface of the roof prism 70. Assuming that the angle of the emitted light beam is 2θ ₁ , it may be set to an angle obtained by the above equation (2).

The first surface 51 and the second surface 51 have such an angular relationship.
In front of the surface 52 (on the subject side), there is a first surface 51
A roof surface 53' as a third surface having two reflecting surfaces that reflects the light beam _P3 totally reflected diagonally backward is formed in place of the third surface 53 shown in FIG. .

In addition, a roof surface 5 is provided at the rear of the roof prism 70.
A fourth surface 54 is formed which emits (transmits) a luminous flux P ₁₀ reflected at 3' and further totally reflected at the first surface 51 to the rear outside as a luminous flux P ₁₁ . An eyepiece lens 55 is disposed behind this fourth surface 54.

Here, the luminous flux reflected by the roof surface 53'
The condition for total reflection of P ₉ by the first surface 51, which is originally a transmitting surface, is that the incident angle θ' of the luminous flux P ₉ is as in the above equation (1), θ'=sin ^{- 1} (1/n) [where n: refractive index].

To explain the operation of the embodiment of the present invention configured in this way, the light beam refracted by the photographing lens 10'
P ₀ is bent upward by the mirror 20 when the mirror 20 is positioned to guide the light beam P ₀ to the viewfinder side, and is imaged on the viewfinder screen 40 .

The light beam transmitted through the finder screen 40 at this time is incident on the first surface 51 of the roof prism 70 and becomes a light beam _P1 . This luminous flux P ₁ is transmitted to the second surface 52
The light is reflected diagonally downward by the
The light beam P ₂ enters the first surface 51 again at an incident angle θ exceeding the critical angle, and is totally reflected forward and diagonally upward by the first surface 51 to become a light beam P ₃ . This light beam P ₃ is reflected backward and diagonally downward by the roof surface 53', which is the third surface, and is incident on the first surface 51 as a light beam P ₃ at an incident angle of θ'. The incident angle θ' at this time satisfies the condition for total reflection as shown in equation (1)' above, that is, the condition that the incident angle θ' is greater than or equal to the critical angle. It is totally reflected and becomes a luminous flux _P10 . This luminous flux P ₁₀ is
The light beam is emitted from the light source 4 toward the rear and becomes a luminous flux _P11 . This luminous flux P ₁₁ is expanded and imaged by the eyepiece 55, and as a result, the eyepiece 55
An erect, normal image (observation image with the left and right sides rotated in the normal direction) can be observed behind the .

According to the embodiment of the present invention constructed and operated as described above, although the roof surface 53' is provided, the roof surface 53' is located not at the top but at the front, and furthermore, the second surface 52 and Since the beam is reflected twice by the first surface 51 and is focused, the height of the roof prism 70 can be reduced and the roof surface can be significantly downsized.

Further, the roof prism 70 has a second surface 52
The luminous flux P ₂ reflected by
This light beam is directed toward the surface 51 of
The light beam P ₂ is totally reflected by the first surface 51 and directed as a light beam P ₃ toward the roof surface 53' diagonally above the front, and this light beam P ₃ is reflected backward for the first time at the roof surface 53'. Therefore, compared to the second conventional example of the finer prism, the dimension in the front and rear directions can be significantly reduced, and the overall shape of the roof prism 70 is simple, eliminating the need to bond multiple prisms together, making it inexpensive. can be produced.

Further, the shape of the roof prism 70, especially the dimension in the front-rear direction, is short, so that the fourth surface (output surface) 54 of the roof prism 70 fits within the width of the camera body (width in the front-rear direction), and the first and second Unlike conventional cameras, the camera body does not have to be large or the eyepiece does not protrude significantly toward the rear, and the amount of protrusion is extremely small, making it easy to use when observing the viewfinder. There is no problem in storing it in a case or carrying it around.

It goes without saying that the present invention is not limited to the above-described embodiments, and may be modified in various ways without departing from the spirit thereof.

For example, a condenser lens, Fresnel lens, etc. may be inserted between the finer screen and the prism.

(e) Effect As described above, the present invention has a simple configuration, and since each reflecting surface is provided integrally, there is no need to bond multiple prisms together, making it possible to manufacture the prisms at low cost. The surface reflects the light beam diagonally forward and downward, the reflected light beam is totally reflected forward and diagonally upward on the first surface, and the reflected light beam is reflected backward and diagonally downward on the roof surface toward the first surface. Therefore, the height dimension of the roof prism can be reduced, and in particular, the dimension in the front-rear direction can be shortened, and the camera can be made smaller accordingly. A roof prism for camera viewfinder that is easy to use when observing the viewfinder because the amount of protrusion can be significantly shortened compared to conventional ones, and that can improve the ease of storage in a camera case or the portability of the camera to which this prism is applied. can be provided.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a single-lens reflex camera using a camera viewfinder prism according to a first embodiment, which is the basis of the present invention;
The figure is a sectional view schematically showing the configuration of a single-lens reflex camera using a camera viewfinder prism according to the second embodiment, which is the basis of the present invention.
1 is a sectional view showing a schematic configuration of a single-lens reflex camera using a roof prism for a camera viewfinder according to an embodiment of the present invention. 10, 10'...Photographing lens, 20...Mirror,
30...Film, 40...Finder screen, 50,60...Prism, 51,61,71
...first surface, 52,62,72...second surface,
53, 63...Third surface, 53'...Dach surface, 5
4, 64... Fourth surface, 55... Eyepiece, 7
0... Roof prism.

Claims (1)

[Scope of utility model registration request] The optical path switching mirror is placed in a position in which the light emitted from the photographic lens is guided to the viewfinder side through a photographic lens and an optical path switching mirror that is sequentially switched between a position where the light emitted from the photographic lens is guided to the film surface and a position where the light emitted from the photographic lens is guided to the viewfinder side. In a roof prism for a camera viewfinder, which uses the object image formed on the viewfinder screen placed at the rear of the optical path as an erect observation image, the light flux that passes through the viewfinder screen on which the object image is formed is a first surface that receives the light beam that has passed through the first surface and reflects it obliquely forward so that it is incident on the first surface again at an incident angle that exceeds the critical angle. 2 and a critical angle to the first surface, which is located in front of the second surface and receives the luminous flux that is reflected by the second surface and further diagonally forwardly reflected by the first surface. A third surface made of a roof surface that reflects diagonally backward so that the beam is incident again at an incident angle exceeding A roof prism for a camera viewfinder, characterized in that the first to fourth surfaces are integrally formed on the surface of one prism.