JPH0313924A - Finder optical system - Google Patents

Abstract

PURPOSE:To make a camera compact a which has the finder optical system independent of a photography optical system and to compensate the parallax excellently by using a wedgelike liquid crystal parallax prism which is provided in such a direction that polarized light passed through a polarizing plate becomes ordinary light or extraordinary light and brought under ON-OFF control. CONSTITUTION:A polarizing plate 11 which passes one linear polarized light beam, a negative lens 13 which has a half-mirror surface 12, the wedgelike liquid crystal prism 14 to be brought under ON-OFF control, a 1/4lambda plate 15, a reflection target 17 for visual field frame display which is provided on a transparent plate 16, and a positive lens 18 are arranged in order form the object side. The wedgelike liquid crystal prism 14 operates as a parallel flat plate to S-polarized light and as a wedgelike prism to P-polarized light. The polarizing plate 11 passes only the S-polarized light or P-polarized light of light from the object side and the switch of the liquid crystal prism 14 is turned on and off to change a visual field direction, thereby realizing the compact finder optical system of simple constitution while the parallax is compensated excellently.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a finder optical system independent of a photographing system.

[Conventional technology]

For cameras such as compact cameras, still cameras, and video cameras that have a finder optical system that is independent of the shooting optical system, the two optical systems cannot be placed on the same optical axis, so the range that can be photographed by the shooting lens is always It is difficult to observe the same landscape. For example, if the optical axes of the photographing lens 1 and the finder lens 2 are parallel as shown in FIG. However, if the subject is close, the amount of deviation between the range that can be photographed with the photographing lens 1 and the range that can be observed with the finder lens 2 becomes large. So-called vararax occurs, and it becomes larger as the subject gets closer.

Therefore, one way to solve this problem is to narrow the distance between the optical axes of both optical systems, which will reduce the variation, but even with this method, at least the lens diameter will be reduced.

This method has its limitations, as it requires a separation equal to the size of the lens frame member.

For example, the amount of balax will be specifically shown using a 35 mm silver halide camera as an example. As shown in FIG. 1O, it is assumed that the photographic lens is a zoom lens with a focal length of 35 to 105 planes, an optical axis interval of 30 mm in the vertical direction, and an object distance of 300 mm.

If the film is 24 mm x 36 mm, the viewing angle in the vertical direction at the wide-angle end is jan -' (12
÷35)X2-38°, and the viewing angle at the far end is ja
n −' (12÷105)x2=13°.

Also, the deviation in the viewing direction between the finder lens 2 and the photographing lens 1 is jan "-'(30+300)", 5.
It becomes 7°.

Therefore, as shown in Figure 11, at the wide-angle end, approximately 15% (5,7 ÷ 38) of the screen in the vertical direction, and at the telephoto end, approximately 40% (5,7 ÷ 13) of the screen in the vertical direction. Vararax occurs respectively.

Therefore, as a means for correcting balax, conventionally the main methods used have been (1) changing the arrangement of the field frame of the finder, and (2) changing the viewing direction by inserting and removing a wedge-shaped prism in front of the finder lens.

[Problem to be solved by the invention]

However, since all of the above means are mechanically driven, there are problems in that the configuration becomes complicated and the overall size of the camera increases.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a finder optical system that has a simple configuration, can make the entire camera compact, and can satisfactorily correct vararax.

[Means and effects for solving the problems] The finder optical system according to the present invention includes, in order from the object side, a polarizing plate that allows one linearly polarized light to pass through and a half mirror surface in the finder optical system that is independent of the photographic optical system. a wedge-shaped liquid crystal prism that is ON-OFF controlled and arranged in a direction such that the polarized light passing through the polarizing plate becomes ordinary light or extraordinary light; a quarter-wave plate; and a reflection for displaying a field frame. By arranging the target and other optical elements that transmit light in the other parts, the refractive power of the wedge-shaped liquid crystal prism can be changed by electrical drive, and the viewing direction can be changed. .

〔Example〕

Hereinafter, the present invention will be described in detail based on an illustrated embodiment.

Fig. 1 shows a finder optical system according to the present invention, which normally passes only S-polarized light, that is, the vibration direction coincides with S-polarized light, and if necessary, rotates 90 degrees around the optical axis, starting from the object side on the left side of the drawing. A polarizing plate 11 that can be rotated to allow only P-polarized light to pass through, and a half mirror surface 12.
A negative lens 13 having a
A wedge-shaped liquid crystal prism 14 that is N-OFF controlled, a λ plate 15, a reflective target 17 for displaying a field frame provided on a transparent plate 16, and a positive lens 18 are arranged.

In this case, light that vibrates in a plane perpendicular to the plane of the paper is S-polarized light, and light that vibrates in a plane parallel to the plane of the paper is P-polarized light.

The wedge-shaped liquid crystal prism 14 is constructed of a parallel transparent plate 19 made of glass, acrylic, etc. and a wedge-shaped prism 20 as shown in FIG.
A transparent electrode 21 and an alignment film 2 are provided on the surfaces facing each other.
2, and nematic liquid crystal 23 is sealed in a wedge-shaped gap in a cell portion formed by the opposing surfaces. Then, the switch SW is turned OFF.
When no voltage is applied (Fig. 2 (A)),
The molecular arrangement of the liquid crystal 23 is such that the direction in which the long axes of the molecules are arranged (rubbing direction) matches the direction perpendicular to the vibration direction of the polarizing plate 11 (vibration direction of S-polarized light), that is, S-polarized light becomes ordinary light and P-polarized light It has a homogeneous arrangement so that it becomes an extraordinary light. Further, the refractive index of the wedge-shaped prism 20 is made to match the refractive index of the liquid crystal 23 for S-polarized light (ordinary light).

Therefore, the wedge-shaped liquid crystal prism 14 acts in the same way as a parallel plate for S-polarized light, and acts as a wedge-shaped prism for P-polarized light. Further, when the switch SW is ON and a voltage higher than a certain value is applied (Fig. 2 (B)), the molecular arrangement of the liquid crystal 23 is homeotropic, that is, the long axis direction of the molecules is S.
Since the arrangement is perpendicular to the vibration directions of both polarized light (ordinary light) and P-polarized light (extraordinary light), the wedge-shaped liquid crystal prism 14 is
It functions in the same way as a parallel plate for both polarized light and P-polarized light.

Next, the principle of operation of this embodiment will be explained.

First, as shown in FIG. 1, the polarizing plate 11 is positioned so as to pass only the S-polarized light from the object side, and the switch SW of the wedge-shaped liquid crystal prism 14 is turned off. Then, the S-polarized light from the object that has passed through the polarizing plate 11 passes through the wedge-shaped liquid crystal prism I4 as a parallel plate, passes through the S λ plate 15, becomes circularly polarized light, passes through the transparent plate 16, and passes through the positive lens 18. be observed. In addition, the circularly polarized light reflected by the reflection target 17 in the light from the object side is again reflected by the %λ plate 1.
5 in the opposite direction and becomes P-polarized light, which is refracted by a wedge-shaped liquid crystal prism 4. Then, it is reflected by the half-mirror surface 12 of the negative lens 13, and further refracted by the wedge-shaped liquid crystal prism 14. It passes through a positive lens 18 and is observed.

The appearance of the image (field frame) of the object image 1 reflecting target 17 at this time is as shown in FIG. 3(A).

Next, as shown in FIG. 4, the switch SW of the wedge-shaped liquid crystal prism 14 is turned on while the polarizing plate 11 remains in the same position. In this state, the wedge-shaped liquid crystal prism 14 acts as a parallel flat plate for both S-polarized light and P-polarized light, so the light reflected by the reflection target 17 is not refracted by the wedge-shaped liquid crystal prism 14 at all. Therefore, the appearance of the image (field frame) of the object image 1 reflecting target 17 at this time is as shown in FIG. 3(B).

Next, as shown in FIG. 5, the polarizing plate 11 is rotated 90 degrees around the optical axis so that only the P-polarized light from the object side passes through, and the switch SW of the wedge-shaped liquid crystal prism 14 is turned.
Turn off. Then, the P-polarized light from the object side is refracted by the wedge-shaped liquid crystal prism 14, passes through the λ plate 15, becomes circularly polarized light, and is transmitted to the transparent plate 16. It is observed through a positive lens 18. Further, the circularly polarized light reflected by the reflection target 17 passes through the %λ plate 15 in the opposite direction again, becomes S-polarized light, and enters the wedge-shaped liquid crystal prism 14. At this time, wedge-shaped liquid crystal prism 1
4 acts as a parallel plate for S-polarized light, so it is not refracted, and the S-polarized light that has passed through is reflected by the half mirror of negative lens 13.
It is reflected by the surface 12, passes through the wedge-shaped liquid crystal prism 14 again without being refracted, and passes through the λ plate 15. Transparent plate 16. It passes through a positive lens 18 and is observed. Therefore, object image 1 at this time
The image (field frame) of the reflective target 17 appears as shown in FIG. 3(C).

The above points will be explained in more detail.

Consider the case where the finder optical system is located above the photographing optical system. For example, in the state shown in Figure 1, when the object is far away, the finder optical system should be adjusted relative to the optical axis of the photographing optical system so that the object and the field of view frame coincide. Tilt the optical axis by an angle α. If the object is close, it will be in the state shown in Figure 4, and if it is even closer, it will be in the state shown in Figure 5.
Set it to the state shown in the figure. By doing so, the field of view frame sequentially moves downward, making it possible to correct vararax.

Conversely, when the object is far away in the state shown in Figure 5, the optical axis of the finder optical system is tilted by an angle β with respect to the optical axis of the photographing optical system, and the wedge-shaped liquid crystal prism is 14 upside down, and as the object approaches, the fourth
Vararax can also be corrected by sequentially switching between the state shown in the figure and the state shown in FIG.

In this way, balarax is well corrected, but according to this embodiment, the refractive power of the wedge-shaped liquid crystal prism 14 is changed by electrical drive to change the viewing direction, so the configuration is simple. Therefore, the entire camera can be made compact. Furthermore, according to this embodiment, the images from FIGS.
When the state changes from Figure 4 to Figure 5, the amount of balax correction for the 2 degrees of refraction is obtained; This is about twice as effective as the amount. Also, Figures 1 to 5
In the state change from FIG. 4 to FIG. 5, a balaxe correction amount that is approximately three times the amount of vararax correction obtained in the state change from FIG. 4 to FIG. 5 is obtained. Therefore, there is no need to particularly increase the apex angle of the liquid crystal cell portion of the wedge-shaped liquid crystal prism 14 to increase the thickness of the liquid crystal cell portion in order to increase the amount of balax correction, so the response speed does not become slow. In addition, in order to prevent a decrease in response speed, the wedge-shaped liquid crystal prism is made into a Fresnel lens shape to prevent the thickness of the liquid crystal cell from increasing, and the image is affected by diffraction and is adversely affected by flare light. will not become unclear.

In this embodiment, the wedge-shaped liquid crystal prism 14 consists of a wedge-shaped prism section and a liquid crystal cell section, but in actual construction, it may also serve as a wedge-shaped prism, as shown in FIG. 6(A), for example. The liquid crystal 23 may be sealed in the case 24, or the liquid crystal 23 may be sealed in the wedge-shaped case 25, and the wedge-shaped prism 20 may be bonded thereto as a liquid crystal cell.

Further, as shown in FIG. 7, the present invention can be satisfied even with a wedge-shaped liquid crystal prism 14 without the wedge-shaped prism 20. In this case, as shown in FIG. 8, the optical axis of the finder optical system 2 may be tilted with respect to the optical axis of the photographic optical system 1 in advance, and the balax can be corrected using that position as a reference. .

Furthermore, instead of rotating the polarizing plate 11, a twisted nematic liquid crystal element may be placed immediately after the polarizing plate 11 and driven to rotate the plane of polarization.

〔Effect of the invention〕

As mentioned above, the finder optical system according to the present invention has a simple configuration, and the entire camera can be made compact.
This has a practically important advantage of being able to satisfactorily correct vararax.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a case where the wedge-shaped liquid crystal prism is turned off in an embodiment of the finder optical system according to the present invention;
Fig. 2 is a diagram showing the specific structure of the wedge-shaped liquid crystal prism of the above embodiment and its operating principle, Fig. 3 is a diagram showing how the object image and field frame appear in the above embodiment, and Fig. 4 is a diagram showing the above embodiment. FIG. 5 is a diagram showing a state in which the wedge-shaped liquid crystal prism is turned ON in the above embodiment, FIG. FIG. 8 is a diagram showing the inclination of the finder optical system when the wedge-shaped liquid crystal prism shown in FIG. 7 is used. FIG. 9 is a diagram showing a conventional example. 11A and 11B are diagrams showing a specific example of the conventional example and the variation at the wide-angle end and the telephoto end in that case. 11...Polarizing plate, 12...Half mirror surface, 1
3... Negative lens, 14... Wedge-shaped liquid crystal prism,
15...Slambda plate, 16...Transparent plate, 17...
・Reflection target, 18...Positive lens, 19...
・Parallel transparent plate, 20... Wedge-shaped prism, 21...
-Transparent electrode, 22...Alignment film, 23...Nematic liquid crystal, 24.25...Case. Figure 1 FF Figure 4 Figure 6 Figure 9 Figure Wide-angle end Telephoto end

Claims (1)

[Claims] In a finder optical system that is independent of the photographic optical system, in order from the object side, a polarizing plate that allows one linearly polarized light to pass through;
an optical element having a half mirror surface; a wedge-shaped liquid crystal prism that is ON-OFF controlled and is oriented such that the polarized light passing through the polarizing plate becomes ordinary light or extraordinary light;
1. A finder optical system comprising a wavelength plate and other optical elements having a reflective target for displaying a field frame and transmitting light in the other parts.