JPH0618343Y2 - Roof reflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shape of a roof-type reflecting mirror used in a viewfinder optical system of a single-lens reflex camera, and particularly to a shape of a side wall portion of the roof-type reflecting mirror.

BACKGROUND ART Conventionally, a glass penta roof prism (hereinafter, referred to as a penta prism) is widely used in a viewfinder optical system of a single-lens reflex camera. In this pentaprism, it is desirable that light rays are not reflected as much as possible on a surface (for example, a side surface portion of the prism) other than the surface that reflects the structure of the finder optical system. This is because the light ray incident on the side surface portion is harmful light that has deviated from the original optical path and appears as a ghost when this light ray reaches the pupil of the photographer. In order to reduce this ghost, the side surface of the pentaprism is generally covered with a black coating film composed of a black pigment and a solvent.

On the other hand, in recent years, with the weight reduction and cost reduction of cameras, instead of the pentaprism, the roof part consisting of two reflecting surfaces intersecting at right angles and the light left-right reversed by this roof part are used in the rear eyepiece. It has been proposed to use a roof reflector having a reflecting surface that reflects.

Similarly to the pentaprism in the roof reflecting mirror, it is desirable that light rays are not reflected as much as possible on the surface other than the reflecting surface as the finder optical system (for example, the inner surface of the side wall portion holding the roof portion). In order to reduce the reflection of light on the side wall, it is conceivable to attach a black coating film to the side wall or attach black flocked paper or black tape, but each requires a separate process. Therefore, it is disadvantageous in terms of assembly man-hours.

The shape of the roof reflector is made by resin molding, and the reflecting surface of the roof is A or Ag.
A method of forming by vapor deposition of is known. Therefore, it is conceivable to reduce the reflection of light on the side wall portion by adding a black pigment to this molding resin to form a black molding.

However, when the roof type reflecting mirror is used instead of the penta prism, the following problems occur.

In the case of a pentaprism, the refractive index of the solvent that covers the side surface is almost the same as that of the glass, and all light rays incident on the glass end face enter the coating film without being reflected at the boundary surface between the glass and the coating film, giving a black It is absorbed by the pigment. On the other hand, in the case of the roof type reflecting mirror, since the inside is hollow, light rays are incident on the resin from the air in the side wall portion. At this time, due to the difference in refractive index between the air and the resin, a part of the light ray is reflected at a portion where the black pigment does not appear on the boundary surface. Therefore, in the case of the roof reflecting mirror, more ghosts are caused due to the reflection of light rays at the side wall portion, as compared with the penta prism.

An object of the present invention is to solve the above-mentioned problems and to provide a roof reflecting mirror capable of reducing a ghost caused by reflection of a light beam on a side wall portion.

In order to achieve the above object, the present invention is characterized in that the side wall portion of the roof reflecting mirror satisfies the following conditions.

-The inner surface of the side wall is a diffusion surface.

・ 80 ° <θ <89 ° where θ is the angle between the side wall and the plane parallel to the focusing screen.

The present invention will be described below. First, by diffusing the inner surface of the side wall portion, the light rays reflected by the boundary surface between air and resin are scattered in all directions, and the specular reflection component is significantly weakened. Therefore, even if a part of the reflected light reaches the photographer's pupil, the ghost that occurs is significantly reduced as compared with the related art.

Further, by making the angle θ formed by the side wall and the plane parallel to the focusing screen smaller than the conventional 90 °, it is possible to keep the ghost generated around the finder screen away from the image frame and make it inconspicuous.

Further, in the case of the roof-type reflecting mirror in which the roof portion and the side wall portion are integrally molded by molding, the following action is achieved in addition to the above-mentioned reduction of the ghost. By making the angle θ smaller than 90 °, the side wall portion becomes a taper and the mold release at the time of molding can be facilitated. Therefore, it can be prevented that extra stress is applied to the molded product when the molded product is taken out from the mold, and the right angle accuracy of the two reflecting surfaces and the flatness accuracy of the reflecting surface are deviated.

Now, the length of the short side of the opening in the roof type reflecting mirror for introducing the observation light from the focusing screen is 24 mm, and the angle formed by the ridgeline formed by the two reflecting surfaces of the roof portion with the horizontal direction is 20 °.
Then, the height required by the side wall in the direction perpendicular to the reticle is 24 × tan20 ° from the trigonometric function formula, which is 8.7.
mm. For the molded roof-type reflector, the accuracy of movement between the mold and the roof-type reflector so that the mold and the roof-type reflector can be easily removed is 0.15 at maximum on one side at the maximum height of the side wall.
If more than mm is required, the angle θ formed by the side wall with respect to the plane parallel to the focusing screen is θ <tan ⁻¹ (8.7 / 0.15), that is, θ <89 °. On the contrary, if θ becomes too small, the side walls will spread too wide on both sides, making it impossible to make the camera compact and lightweight. Therefore, if the width of the side wall is limited to within 1.5 mm on one side, θ <tan ^-1 ( 8.7 / 1.5) That is, θ <80 °. That is, the allowable range of θ is as follows.

80 ° <θ <89 ° (I) Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a roof portion (1) and a side wall portion (2) of an integrally molded roof reflecting mirror showing an embodiment of the present invention,
θ is the angle that the side wall (2) forms with the plane parallel to the focusing screen. As shown in Fig. 2, the roof type reflector (4)
The mold part (3) and (5) mold the roof part and the side liquid part integrally. In the example, since θ = 86 °, the mold
When taking out the roof reflector (4) from (3) and (5), it is possible to remove it without the side wall part getting caught in the mold (5). The plane accuracy of the surface is maintained at the processing accuracy of the molds (3) and (5).

Further, when the roof reflecting mirror is used in the viewfinder optical system of a single-lens reflex camera, a harmful ghost is generated in the viewfinder due to the side wall. The ghost will be described below with reference to the drawings.

FIG. 3 is a view showing the paths of a normal ray and a ghost ray, which are traced backward from the pupil when a conventional finder optical system is constructed by a roof-type reflecting mirror whose side wall is perpendicular to a focusing screen. Further, FIG. 4 is a diagram showing a ghost that the light beam in the case of FIG. 3 creates on both sides in the finder. The rays of (a) to (e) shown in FIG. 3 correspond to the normal angle of view of FIG. 4 (a) and the ghosts of (b) to (e), respectively.
Here, (6) is the reflecting surface A that constitutes the roof portion, and (7) is the reflecting surface A.
A reflecting surface B having an angle at right angles with, (8) is a field frame, and (9) is a focusing screen. When (a) to (e) in FIGS. 3 and 4 are traced backward from the pupil, they are first reflected by the second reflecting surface and then reflected by the reflecting surface A to reach the optical path as shown in FIG.

That is, (a) a light ray that is reflected by the reflection surface B and reaches the field frame. (B) a light ray that is reflected by the reflection surface B and is reflected by the side wall and reaches the focusing screen. Rays of light that are reflected and reach the focusing screen (d) Do not pass through the reflecting surface B and rays of light that reach the field frame (e) Do not pass through the reflecting surface B and reach the focusing screen directly. Of these, (d) is far from the screen. Since it is weak, (e) is far from the screen and it will be blurred by the shooting lens when the shooting lens is attached, so it is not conspicuous respectively, so the ghost that becomes a problem when using the roof reflector is (b) , (C) are made by reflecting on the side wall.

As shown in FIG. 5, the side surface of the glass penta roof prism is generally covered with a black coating film (11) composed of a black pigment (12) and a solvent (13). At this time, the refractive index of the solvent is selected to be almost equal to the refractive index of the glass, so as shown in the figure, the light rays incident on the glass end face are not reflected at the boundary surface between the glass (10) and the coating film. Since all the light enters the coating film and is absorbed by the black pigment, the ghosts (b) and (c) cannot be seen on the glass penta roof prism. On the other hand, the roof reflecting mirror is formed by resin molding, and is formed by vapor deposition of the reflecting surface A or Ag forming the roof portion. Since the inner surface of the roof-type reflecting mirror other than the reflecting surface does not reflect incident light, there are various possibilities such as attaching a black coating film, sticking black flocking paper, or sticking a black tape, but such work is Since it is a separate process and is disadvantageous in terms of work, it is the sixth step in this embodiment.
As shown in the figure, a black pigment (16) is put in the molding resin (17) to form the roof-type reflecting mirror itself into a black molded article so as to obtain an antireflection effect.

However, since the inside of the roof-type reflecting mirror is hollow, when a light ray enters from the air (14) into the side wall part (15), which is a black molded product, the black pigment is applied to the boundary surface due to the difference in refractive index. A part of the light ray is reflected at the part that does not come out and becomes a ghost.

The reflecting surface is expressed by the following equation for normal incidence.

Where n _{1 is} the refractive index on the incident side, n _{2 is} the refractive index on the exit side, and assuming that the refractive index n _{2 of the} resin is 1.5, the refractive index of air is n.
_{Since 1} = 1, R = 0.04, and about 4% of the incident light is reflected. In reality, there is only a small amount of pigment on the boundary surface, so it is not possible to completely eliminate the reflected light. Therefore, in the present invention, as shown in FIG. 7, by using the resin surface on the inner surface of the side wall of the roof-type reflecting mirror as a diffusing surface, the specularly reflected light component is greatly reduced and the bright ghost is invisible. I am trying.

In this way, when ghosts caused by the side wall of the roof-type reflecting mirror are prevented by making the inner surface of the side wall a diffusion surface, the angle θ formed by the side wall and the plane parallel to the focusing screen is The following condition (II) is particularly preferable in place of the condition (I).

80 ° <θ <87 ° (II) The following effects can be obtained by the configuration of the present invention as described in detail above.

First, by diffusing the inner surface of the side wall portion, the light rays reflected by the boundary surface between the air and the resin are scattered in all directions, and the specular reflection component is significantly weakened. Therefore, even if a part of the reflected light reaches the photographer's pupil, the ghost that occurs is significantly reduced as compared with the related art.

Further, by making the angle θ formed by the side wall portion and the plane parallel to the focusing screen smaller than the conventional 90 °, it is possible to reduce the ghost generated around the finder screen from the image frame.

Further, in the case of the roof-type reflecting mirror in which the roof portion and the side wall portion are integrally molded by molding, the angle θ is set to 90.
By making it smaller than 0 °, the side wall portion becomes a taper, and the mold release during molding can be facilitated. Therefore,
It can be prevented that extra stress is applied to the molded product when the molded product is taken out of the mold, and the right angle accuracy of the two reflecting surfaces and the flatness accuracy of the reflecting surface are deviated.

[Brief description of drawings]

FIG. 1 is a sectional view of a molded roof reflector, FIG. 2 is a sectional view of a mold and a roof reflector molded by the mold, and FIG.
Figure shows the ghost rays seen in a conventional roof reflector, Figure 4 is a view inside the viewfinder when a conventional roof reflector is used, and Figure 5 is a side view of the glass penta roof prism. Fig. 6 shows the side wall of the roof reflector, and Fig. 7 shows the side wall with a diffusing surface. 1 …… Roof reflector roof, 2 …… Roof side wall θ: Angle formed by the side wall and the plane parallel to the focusing screen

Claims (1)

[Scope of utility model registration request] 1. A viewfinder of a single-lens reflex camera in which a roof portion 1 having two reflecting surfaces 6 and 7 intersecting each other at a right angle and a side wall portion 2 holding the roof portion 1 are integrally molded by molding. In the roof type reflecting mirror 4 to be used, the side wall portion 2 has a diffusing surface on the inner surface thereof and satisfies the following conditions: 80 ° <θ <89 ° where θ is a side wall The angle between the part 2 and the plane parallel to the focusing screen 9.