JPH0237333A - Finder equipped with polarization eliminating plate - Google Patents

Abstract

PURPOSE:To prevent failure due to incidence of linear polarized light even if optical element such as plastic parts prone to generate optical elastic distortion and a half mirror with polarization characteristics are used by arranging plural polarization eliminating plates on an optical axis in a find by means of shifting their crystals axes. CONSTITUTION:At least two polarization eliminating plates 6 are superposed and disposed on the optical axis of the finder so that their crystal axes have prescribed angles. Since the light beams made incident on the finder are made incident on an objective lens 1 through the two converted polarization eliminat ing plates 6, even though linear polarized light enters the finder, the beams turn into light beams with disturbed polarization characteristics and passe by the objective lens 1 and thereafter. Thus, trouble arising when linear polar ized light enters can be reduced significantly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a finder optical system suitable for compact cameras, video cameras, electronic cameras, and the like.

[Conventional technology]

Generally, the finder optical system of compact cameras, video cameras, electronic cameras, etc. often uses either the Albada type, reverse Galileo type, or Kevlar type (real image type). Some use an erecting prism to achieve this. For example, in the previously filed Japanese Patent Application No. 32868/1986, the present applicant introduced a method for distributing light rays to a light receiving element using a finder that incorporates a photometric element into an erecting prism and using a half mirror on the reflective surface of the prism. are doing. This configuration will be explained using FIG. 9.

On the same optical axis, there is an objective lens 1 closest to the object, and behind it there is a four-time reflection prism, or Porro prism 2, which functions to invert the image formed by the objective lens 1 vertically and horizontally to make it erect. , a half mirror 3 is provided on the fourth reflective surface of the Porro prism 2. The half mirror
A light-receiving element 4 is provided in the direction in which the light transmitted through the lens 3 travels, and an eyepiece 5 is provided in the direction in which the reflected light travels. The light reflected from the object passes through the objective lens 1 and enters the Porro prism 2.
A real image is formed near the plane of incidence. Next, the light beam enters the end face of the Porro prism 2 and is sequentially reflected from the first to third reflecting surfaces, and then is split into two by the half mirror 3, and the transmitted light enters the light receiving element 4. The reflected light is observed through the eyepiece 5.

[Problem to be solved by the invention]

The half mirror as described in the above prior art is
In order to avoid absorption effects, half mirrors are often made of dielectric thin films, and as a result, the half mirror itself has polarization characteristics. However, the patent application 1986-328
In the specification of No. 68, no consideration is given to the polarization characteristics of the half mirror, and the following problems may occur depending on the state of the incident light beam. In other words, this phenomenon occurs when a polarizing mirror is used in a camera finder. For example, when a ray of light with a polarized state that is different from linearly polarized light, such as light from the blue sky or light reflected from the water surface, enters the finder, Since the incident light reaches the light receiving element after passing through a half mirror, which is a polarizing mirror, the incident light passes through the polarizing mirror and the amount of light received by the light receiving element changes depending on the direction of polarization of the incident light. have. Similarly, even if a mirror without polarization properties is used, if the light receiving element has polarization properties, exactly the same phenomenon as described above will occur.

Also, if prisms are made of glass, it is difficult to mass produce and the weight increases, so they are often made with plastic molds, which are easy to mass produce, lightweight, and have low material costs. The disadvantage is that residual stress tends to occur internally. For this reason, if a polarizing mirror is installed closer to the eyepoint than the finder prism, when a light beam with a polarization state close to linear polarization, such as light from the blue sky or reflected light from the water surface, enters, the polarizing mirror becomes the analyzer. A problem arises in that the photoelastic strain caused by the residual stress within the prism becomes visible when the prism acts as an analyzer. This also means that when a light receiving element is provided on the eye point side of the polarizing mirror, the amount of received light may vary depending on the workmanship of the prism.

On the other hand, as a means to eliminate linearly polarized light, in fields such as microscopy, it is possible to convert linearly polarized light into circularly polarized light by installing a 174-wave plate in the optical path, and to change the polarization state by using a depolarizing plate. Disturbing is the special public service 1986-5168
It is known from Publication No. 7, etc.

Considering the application of this conventional technology to the finder of a camera, both the 174-wave plate and the depolarizer are effective for a certain direction of the polarization plane, but the vibration direction of the polarization of the incident light and the quarter-wave plate and the depolarizer are effective. The bottleneck is that when the crystal axis direction of the depolarizing plate matches, the incident light rays pass through without being affected by anything. This did not occur because the camera can be controlled in advance, but it cannot be avoided because the camera must be used in various orientations to suit the subject, which changes in all directions. It is not possible to resolve the 8 points between polarizing mirrors.

The present invention has been made in view of these problems, and provides a finder that solves all of the problems caused by the polarization of the finder described above by skillfully applying a depolarizing plate to the finder system. The purpose is to

[Means to solve the problem]

In order to achieve the above object, the finder according to the present invention is provided in a camera finder such that the crystal axis is perpendicular to the optical axis of the finder, as shown in the first embodiment shown in FIG. The present invention is provided with at least two depolarizing plates arranged so as to overlap each other on the optical axis of the finder so that their crystal axes make a predetermined angle to each other.

More preferably, the number of depolarizing plates disposed on the optical axis of the finder is one (n is an integer of 2 or more).
It is preferable to dispose the depolarizing plates with their crystal axes shifted by about 90/n degrees [Function] The function of the present invention will be explained with reference to FIGS. 2 and 3.

Figures 2 and 3 both illustrate the case where two depolarizing plates are made at an angle of 45'' with respect to each other's crystal axes.To simplify the explanation, the depolarizing FiA The crystal axis of the depolarized FiB is parallel to the Y axis, and therefore the crystal axis of the depolarized FiB makes an angle of 45 mm with the Y axis.The polarization state of the light beam on the polarization plane is shown by the straight line The arrow of
Although linearly polarized light is represented, an elliptical arrow represents a state in which linearly polarized light is canceled.

FIG. 2 shows a case where a light beam whose polarized vibration plane is parallel to the Y-axis is incident. In the depolarizing plate A, the light beam passes through without rotation of the plane of polarization. However, in the depolarizing plate B, rotation of the plane of polarization occurs, and the polarization of the light beam is disturbed.

This is referred to as Example 1.

FIG. 3 shows a case where a light beam having polarization that forms an angle of 45 degrees with the Y axis is incident. First, rotation of the plane of polarization occurs in the depolarizing plate A, and further rotation of the plane of polarization occurs in the depolarizing plate B, disrupting the polarization of the light beam. This is called Example 2.

Also, for linearly polarized light whose vibration direction is neither parallel to the Y-axis nor 45 degrees to the Y-axis, each depolarizer plate acts intermediate between Example 1 and Example 2 to polarize the light. A rotation of the plane occurs and the direction of vibration of the light beam is disturbed.

From the above, for linearly polarized light in any direction, A
, B. It can be seen that the polarization is eliminated by passing the light through two depolarizing plates.

The same applies to the case where three or more sheets are stacked.

Furthermore, if the deviation angle of the crystal axes of each depolarizing plate is approximately 90/n degrees, no matter which linearly polarized light is incident on the linearly polarized light with various directions, it will be It is more effective because the polarization characteristics are uniformly disturbed.

〔Example〕

Hereinafter, the present invention will be described in detail based on the illustrated embodiment, with the same reference numerals assigned to the same members as in the above-described conventional example.

A first embodiment of the present invention is shown in FIG. 1. In this embodiment, a rolled polycarbonate film as shown in FIG. 4 is placed on the object side of the objective lens l of the conventional example shown in FIG. Two plates are cut out to have the same shape by changing their orientation by 45 degrees with respect to the crystal axis, and the two plates are laminated together to provide a depolarizing temporary 6. In this way, in this embodiment, all the light beams that enter the finder pass through the two-ply depolarizing plate 6 and enter the objective lens 1, so even if linearly polarized light enters the objective lens 1. All light that passes through it passes as a ray with disturbed polarization characteristics. Therefore, in the Zero1jJI invention, the problematic problem that occurs when linearly polarized light is incident can be completely eliminated.

FIG. 5 shows a second embodiment of the present invention. This embodiment differs from the conventional example shown in FIG.
Is it on the object side of the optical element where residual stress occurs? jl A two-layer depolarization plate 6 is provided in front of the roughly shaped prism 2. As described above, in this embodiment, since the two-ply depolarizing plate 6 is provided on the image side of the objective lens l, by arranging it close to the prism 2, the movement of the objective lens l during zooming can be controlled. Space is secured and suitable for downsizing.

In the case of this example, the linearly polarized light incident on the finder is
After passing through the objective lens l, it is disturbed by a two-ply depolarizing plate 6,
The light rays that reach the prism 2 and the half mirror 3 become light fluxes that do not cause the problems described herein. Therefore,
Even if linearly polarized light enters the finder of this example,
FIG. 6 shows that the problems described in this specification are completely eliminated.
This shows a third embodiment of the present invention. In this embodiment, two depolarizing plates 6 are attached between the first to third reflective surfaces of the prism 2 and the fourth reflective surface on which the half mirror made of a dielectric thin film is disposed. , which is perpendicular to the optical axis of the finder.

In this embodiment, there is a half mirror on the optical axis, which completely limits the movement space of the objective lens 1.
3, the linearly polarized light is disturbed before reaching the half mirror 3. Therefore, the problem that the amount of light flux incident on the light receiving element 4 and the eyepiece 5 changes depending on the vibration direction of the linearly polarized light does not occur.

Furthermore, even if residual stress exists in the objective lens l or prism 2 and photoelastic distortion occurs due to linearly polarized light, the imaging light flux will reach the eyepiece 5 after passing through the two-ply depolarizing plate 6. , the photoelastic strain becomes completely invisible.

Here, in the first to third embodiments, the two-layer depolarizing plate 6 is provided perpendicularly to the optical axis, but in particular, the optical axis and the two-layer depolarizing plate 6 are provided perpendicularly to the optical axis. They do not need to intersect at right angles, and an example of this is shown in the fourth embodiment shown in FIG. Furthermore, a half mirror 3 made of a dielectric material is provided on the image side surface of the two-ply depolarizing plate 6. In this embodiment, the prism 2 has an integral structure.
Two sheets of depolarizing plate 6 and half mirror 3 are pasted on the fourth reflective surface of
Since the prism 2 does not require any complicated processing, the prism 2, the two depolarizing plates 6, and the half mirror 3 are integrated, which saves both space and structure. can also be used as is in the conventional example shown in FIG. Furthermore, regarding the effect of disturbing linearly polarized light, there is no difference from the third embodiment.

FIG. 8 shows a fifth embodiment in which a two-layer depolarizing plate 6 is used in a finder optical system other than the conventional example shown in FIG. 9.

This is a finder optical system that includes, from the object side, a two-layer depolarizing plate 6, an objective lens 1, and an eyepiece 5 having a polarizing mirror 3 disposed internally at a predetermined angle with respect to the optical axis. . This example shows a case where residual stress exists in the lens system and photoelastic distortion becomes visible. The operation of this embodiment is similar to that of the first embodiment,
All the incident light flux passes through the two-ply depolarizing plate 6 and passes through the lens system after the objective lens L, so after the linearly polarized light is disturbed, it passes through the lens with residual stress and the polarizing half mirror. Therefore, the problem caused by linearly polarized light described in this specification does not occur at all. In addition, since the two-layer depolarizing plate 6 is tilted at a predetermined angle with respect to the optical axis, only a portion of the incident light beam is absorbed by the objective lens. The problem that the light reflected at the input end face of the two-layer depolarizing plate 6 and reflected at the output end face of the two-ply depolarizing plate 6 enters the objective lens l and causes a ghost in the imaging light beam does not occur.

That is, even if a part of the incident light is reflected by the objective lens 1, 2
Since the sheet depolarizing plate 6 is tilted, the light reflected thereon is reflected tilted, so that it does not enter the objective lens 1 in the visual axis direction again, and ghosts can be reduced.

In each of the above-mentioned embodiments, it is preferable to arrange display members such as a distance measuring frame and a field frame on the bonding surface of the two-ply depolarizing plate 6 to prevent dust and the like from adhering to the number line display section.

In addition, in Figure 4, the two sheets cut out from polycarbonate do not have to be of the same shape or are pasted together, as long as they can finally disrupt the linearly polarized incident light, so the effective diameter of the incident light beam can be changed. As long as the two sheets are large enough to cover each other and provided on the same optical axis, there is no problem even if the two sheets are not pasted together and are separated. Further, this is not limited to the case where there are two depolarizing plates, but the same can be said when there are three or more depolarizing plates bonded together.

〔Effect of the invention〕

As described above, the finder optical system of the present invention disturbs the linearly polarized light of the passing light by arranging a plurality of depolarizing plates on the optical axis in the finder with their respective crystal axes shifted. Even if the finder uses an optical element such as a brass tink component that is prone to photoelastic distortion or a half mirror that has polarizing properties, there will be problems due to the incidence of linearly polarized light, i.e. things that are visible, such as reflections on the water surface, will not be visible.

■The values of light-receiving elements, etc. that have polarization characteristics are distorted.

■If a light-receiving element is placed after a half mirror with polarization characteristics, the value will be distorted.

■A half mirror with polarization properties acts as an analyzer,
Photoelastic distortion of the plastic parts on the object side of the half mirror can be seen.

It has the advantage of being able to solve problems such as.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the finder optical system according to the present invention, and FIG. 2 shows an incident light beam having the vibration direction of polarized light equal to the direction of the crystal axis of the first sheet of the depolarizing plate. The principle diagram of time, Figure 3, shows that the vibration direction of the polarized light in Figure 2 is 4.
A diagram of the principle when tilted by 5 degrees, FIG. 4 shows an example of a bonded depolarizing plate, and FIGS. 5 to 7 show second to fourth embodiments of the finder optical system according to the present invention. FIG. 8 is a schematic sectional view showing the finder optical system of the embodiment shown in FIG. 5 of the present invention, and FIG. 9 is a perspective view of the conventional finder optical system. Objective Lens Prism Half Mirror Light Receiving Element Eyepiece 2 Pieces Depolarizing Plate Patent Pressure 1 Kaijin Olympus Optical Industry Co., Ltd. 1 Prisoner Figure 2 Figure 5 Section 4 Figure 8 Figure 6 Procedural Amendment Document 1986 10 March 31, 1, Display of the case Patent Application No. 187823 of 19872, Name of the invention Finder 3 with a depolarizing plate, Person making the amendment Relationship to the case Patent applicant 2-chome Hatagaya, Shibuya-ku, Tokyo 151 043 No. 2 (self-proposed) 5. No number of claims increased by the amendment. ``Claims column'' and ``Detailed description of the invention column'' of the specification subject to the amendment. 7. Contents of the amendment (1) ) The scope of claims is amended as attached. (2) Change “occurrence of absorption effect” on page 3, line 5 of the specification to “
``This means that a high absorption rate occurs in itself.'' (3) "The light-receiving element" in the first line of page 4 of the specification is corrected to "the light-receiving surface of the light-receiving element." (4) On page 4 of the specification, lines 18 and 19, "This means that the amount of light received may vary depending on the workmanship of the prism." This means that there is a possibility that there is no light, or that the amount of light received varies depending on the degree of light." (5) Page 6, line 7 of the specification [The first embodiment is shown on the right in FIG. 4" is corrected to "in each of the Examples described below." (6) Delete the phrase "The crystal axis is arranged perpendicular to the optical axis of the finder" in lines 8 to 10 of page 6 of the specification. (7) "On the plane of polarization" on page 7, line 5 of the specification is corrected to "on a plane parallel to the plane of polarization." (8) Change “Ote” from line 3 to line 4 on page 9 of the specification to “
against,” he corrected. (9) "It can be completely eliminated." on page 9, lines 13 and 14 of the specification is corrected to "it can be significantly reduced." (lO) Lines 8 and 9, page 10 of the specification. ``The result is a light flux that does not cause the problems described in this specification.'' is corrected to ``The result is a linearly polarized, disturbed light flux.'' (11) On page 10, line 11 of the specification cylinder, change "The problems described in this specification will be completely eliminated" to "The problems described in this specification [the problem to be solved by the invention] can be significantly reduced." ”, he corrected. (12) “On the optical axis” on page 10, line 19 of the specification
is corrected to "on one optical axis." (13) “It will not happen.” on page 11, line 4 of the specification is r
significantly reduced. ” he corrected. (14) "Completely" on page 11, line 9 of the specification is "habo"
I am corrected. (15) On page 12, line 7 of the specification, ``There is no change.'' is corrected to ``It can be configured to be equivalent.'' (16) "Not occurring at all" in the second and third lines of page 13 of the specification is corrected to "significantly reduced." (17) Delete ``The incident light beam is reflected by the incident end surface of the objective lens 1'' in the fourth and fifth lines of page 13 of the specification. (18) Delete "outgoing end surface" on page 13, line 6 of the specification. (19) On page 13, line 9 of the specification, “that is,” is replaced with “for example,”
” is corrected. Scope of claims

Claims (1)

[Claims] In a finder for a camera, at least two depolarizing plates are arranged so that their crystal axes are perpendicular to the optical axis of the finder, and are placed on the optical axis of the finder so that their crystal axes make a predetermined angle to each other. A viewfinder equipped with a depolarizing plate placed over the top.