JPS6160420B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus display device for a single-lens reflex camera, and more particularly to an improvement in a focusing screen.

Generally, a focusing screen is inserted into the viewfinder system of a camera, and an image of the subject is formed on the matte surface of this screen to perform so-called focusing. Using such a screen allows you to observe the degree of blur, etc. in a state close to that of a real photograph, and it is most commonly used because it does not cause vignetting due to the iris diaphragm of the lens. , there is a drawback that the image becomes dark.

On the other hand, if a focusing screen is not used or a transparent screen is used, a bright and clear aerial image can be observed through the eyepiece of the viewfinder. However, in this case, since the image is not formed on the screen, it is not possible to determine the degree of blur, and it is not possible to perform focusing. Another disadvantage is that vignetting tends to occur due to differences in iris apertures.

The present invention has been proposed based on the above idea, and its purpose is to enable easy focusing by forming an image on a focusing screen, and to make the focusing screen transparent at the same time as the in-focus state is detected. To provide a focus display device for a single-lens reflex camera, which allows a bright and clear image to be observed through a viewfinder.

Hereinafter, details of the present invention will be explained based on embodiments shown in the drawings.

Figure 1 shows the schematic configuration of the finder system, where 1 is a photographing lens, 2 is a mirror, 3 is a focusing screen, 4 is a condenser lens,
5 is a pentaprism, and 6 is an eyepiece. A half mirror 8 is provided at the center of the mirror 2, and a small mirror 9 is attached behind the half mirror 8. Further, a light receiving element 10 for receiving the reflected light from the mirror 9 is disposed below the mirror 2. Furthermore, inside the camera body, there are provided an arithmetic circuit 12 which together with the light receiving element 10 constitutes a focus detection means 11, a voltage application circuit 14 and a battery power supply 15 which constitute a voltage application means 13.

As shown in FIGS. 2 and 3, the focusing screen 3 has a frame 16 sandwiched between a pair of transparent electrodes 17a and 17b, and a liquid crystal 1 between the two electrodes.
8 is inserted, and each transparent electrode 17a, 1
7b is connected to the battery power supply 15 via the voltage application circuit 14. Moreover, each electrode 17a, 1
Transparent plates 19a and 19b are bonded to 7b, and a field mask 20 indicating the photographing range is bonded to the outer surface of one of the transparent plates 19a. Note that each of the transparent plates 19a and 19b is made of a material such as glass or acrylic.

Therefore, the light incident from the photographing lens 1 is reflected by the mirror 2 and directed upward, and part of the light passes through the half mirror 8 and is reflected by the small mirror 9, and directed downward.
The reflected light from the mirror 2 forms an image on the liquid crystal 18 of the focusing screen 3, which can be observed through the eyepiece 6 of the viewfinder.

On the other hand, the reflected light from the small mirror 9 is transmitted to the light receiving element 10.
The light receiving element 10 outputs the light to the arithmetic circuit 12. Then, in the arithmetic circuit 12, the light receiving element 10
When the input from the voltage reaches the set value, a detection signal is output to the voltage application circuit 14,
Drive 4. As a result, a predetermined voltage is applied between the electrodes 17a and 17b of the focusing screen 3, and the liquid crystal interposed between the electrodes 17a and 17b becomes transparent.

Therefore, at the same time that the image on the focusing screen 3 comes into focus, the arithmetic circuit 12
If the camera is configured to output a detection signal, the photographer operates the photographic lens 1 while observing the image on the screen 3 through the eyepiece lens 6 of the viewfinder.
When the focusing screen becomes transparent, it can be detected that a focused state has been reached. After this, a bright and clear aerial image can be observed through the transparent screen 3.

As described above, according to the focus display device of this single-lens reflex camera, by observing the image on the liquid crystal of the focusing screen 3, it is possible to observe the degree of blur, etc. in a state close to that of the actual photograph. Moreover, since vignetting does not occur due to the crimson diaphragm of the lens, focusing can be performed easily. And in the focused state, screen 3
It turns transparent, allowing you to observe a bright and clear aerial image.

Note that the present invention is not limited to the above embodiments,
Can be modified in various ways. For example, in the embodiment described above, the liquid crystal 8 was inserted over the entire surface of the screen 3, but instead of the frame 16, a translucent focusing glass 22 having a small hole 21 and a matte surface as shown in FIG. 4 was used. Alternatively, the liquid crystal 18 may be placed in the small hole 21 and sandwiched between two transparent electrodes 17a and 17b. In this case, when the in-focus state is reached, the small hole 21
Only that part will change to transparent. Further, at this time, the small hole 21 can also be used as an indicator of the focus detection range.

Further, the position of the light receiving element 10 is not limited to the above embodiment, and it is also possible to attach it to the screen 3.

As detailed above, according to the present invention, a focusing screen in which a liquid crystal is interposed between a pair of transparent electrodes is used, and the focus state of an image on the screen surface is detected by a focus detection means, A focus display device for a single-lens reflex camera that has a desired effect by applying a required voltage between the two electrodes by a voltage applying means only when an image is in focus, thereby changing the liquid crystal to transparency. can be provided.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration explanatory diagram showing one embodiment of the present invention, Fig. 2 is a perspective view of the main part of the same embodiment, Fig. 3 is a vertical sectional view of the main part of the same embodiment, and Fig. 4 is a diagram showing another main part of the embodiment. FIG. 2 is a partial perspective view showing an example. 3... Focusing screen, 10... Light receiving element, 11... Focus detection means, 13... Voltage application means, 17a, 17b... Transparent electrode plate, 18... Liquid crystal.

Claims (1)

[Claims] 1. A focusing screen in which a liquid crystal that can change between a diffusion surface and a transparent surface depending on an applied voltage is inserted between a pair of transparent electrodes, and the liquid crystal surface is used as an image forming surface; Voltage application means for applying a required voltage between both electrodes of the focusing screen, focus detection means for outputting a detection signal when detecting the focused state of the subject, and detection of the liquid crystal in the focusing screen. When no signal is output, on the diffusion surface,
A focus display device for a single-lens reflex camera, further comprising control means for controlling the voltage application means so as to change the surface to a transparent surface when a detection signal is output. 2. The voltage applying means comprises a power source and a voltage applying circuit connected to the power source and applying a required voltage between the two electrodes upon receiving a predetermined detection signal. Focus display device for single-lens reflex cameras. 3. A patent claim characterized in that the focus detection means comprises a light receiving element that receives light incident from the photographic lens, and an arithmetic circuit that outputs an output to the voltage applying means when the output of the light receiving element reaches a set value. A focus display device for a single-lens reflex camera according to item 1. 4. The focusing screen is characterized by comprising a translucent focusing glass with a matte surface formed on its surface and a transparent hole in the center, and a liquid crystal disposed corresponding to the transparent hole. A focus display device for a single-lens reflex camera according to claim 1.