JPH01170922A - Camera - Google Patents

Abstract

PURPOSE:To form an exposure controlling mechanism of inexpensive constitution without making the mechanism complicated or large by using an optical element which has adhered or mixed material that changes transmissivity by reacting to light from an object to be photographed for an optical system as a camera composing element. CONSTITUTION:A photochromic glass which has mixed photochromic material whose transmissivity changes reacting to the brightness of the light from the object to be photographed is used for a photographing lens 2, one or more photographing lenses for a finder 3 and an window glass of a light emitting window for AF or light receiving lens. The transmissivity of the photochromic glass is the same as a normal glass when weak light is applied, however, when strong light is applied, the density increases. The glass density increases almost in proportion to the incident light, and the glass has the characteristic of keeping the strength of the transmitted light almost stable, and the exposure control range of the camera is widened. Thus, the exposure control mechanism is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical system of a camera for taking photographs.

[Conventional technology]

In addition to a photographic optical system, the optical system of a conventional camera includes a finder system or an optical system for automatic focusing (hereinafter referred to as AF).

The above-mentioned photographic optical system has an exposure control mechanism built in, and automation is progressing, but it can be broadly classified as follows.

(1) In general, the appropriate exposure amount is obtained by controlling the combination of the exposure time by the shutter and the F number of the optical system.

(2) In the case of the popular type, a program shutter with a predetermined combination of exposure time and F number is generally used to obtain an appropriate amount of exposure.

FIG. 5 is a diagram showing the exposure control curve of the above-mentioned popular type camera, where the vertical axis is the F number, the horizontal axis is the exposure time (Sec), and the numerical values on the diagonal line indicate the brightness of the subject when the subject is photographed using a photosensitive material with an exposure index of 100. It is a numerical value expressed in exposure value (Ev) that provides an appropriate exposure when photographing (hereinafter referred to as subject brightness expressed in Ev). Exposure time is 1/30s with this camera.
When using ec, F number is 2.8, exposure time is 1/700 sec.
This indicates that it is possible to photograph subject brightnesses from Ev8 to Ev17 using a program shutter with an F number of 13.

(3) In the case of a simple type, the exposure control mechanism is simplified,
A fixed F number and exposure time are used, depending on the latitude of the photosensitive material.

FIG. 6 is a diagram showing an example of the exposure error of the above-mentioned simple type camera, where the vertical axis represents the exposure error (Ev), and the horizontal axis represents the subject brightness as the exposure value (Ev), as in FIG. This figure shows the exposure error for a photosensitive material with an exposure index of 400 when the F number IC exposure time is fixed at 1/125 sec. Photosensitive materials with a wide latitude have a tolerance range of ±3Ev, so the range shown by diagonal lines in the figure (Ev9 to Ev
15) can be used.

In conventional cameras, exposure is controlled by adjusting the F number of the lens and the exposure time of the shutter as described above, and there is no camera that controls exposure by controlling the transmittance of the subject light of the photographic optical system. Ta. In addition, the finder optical system and AF
There is no one that changes the transmittance of the optical system depending on the brightness of the subject.

[Problems to be Solved by the Invention] The exposure control method for a general camera described in (1) above has the problem that the control mechanism is complicated, large-sized, and costly.

Furthermore, in the exposure control methods shown in (1) and (2) above,
There was a problem that it was not possible to deal with a wide subject brightness range.

Furthermore, the mark finder has the problem that the mark becomes harder to see as the subject side becomes brighter, and the output of the light receiving section of the AF optical system saturates as the subject brightness increases, reducing accuracy. There was a problem with that.

The present invention has been made to solve these problems, and an object of the present invention is to provide a camera equipped with an exposure control mechanism that is inexpensive and does not require a complicated or large-sized mechanism.

[Means for solving problems]

The above object is achieved by a camera characterized in that an optical system as a component of the camera uses an optical element to which a substance whose transmittance changes in response to subject light is attached or mixed.

〔Example〕

FIG. 1(a) is a perspective view showing one embodiment of the present invention.

In the figure, 1 is the camera body, 2 is the photographing lens, 3 is the finder, 4 is the AF light receiving window in which a position detection element such as a PSD is arranged through the light receiving lens at the rear, and 5 is the infrared emitting LED, etc. at the rear. This is a light-emitting window for an AP in which a light-emitting element is arranged through a light-emitting lens.

One or more of the taking lenses of the taking lens 2 and the finder 3, and the window glass or light receiving lens of the AF light emitting window 4 are mixed with a photochromic substance whose transmittance changes in response to the brightness of the subject light. Otokuromitsuku glass is used. The transmittance of this 7 otochromic glass is the same as that of ordinary glass when exposed to weak light, but when exposed to strong light, the transmittance decreases and the density increases), as shown in Figure 2. It shows a spectral transmittance curve like this and is almost neutral. Furthermore, since the density increases almost in proportion to the intensity of incident light and has the property of keeping the intensity of transmitted light almost constant, it becomes possible to expand the exposure control range of the camera. In a general camera, it is possible to photograph a high-brightness subject without using a high-speed shutter or a lens that can narrow down to a large F number.

Figure 3 is a diagram showing the exposure control curve when 7 otochromic glass is used for the photographing lens of the above-mentioned popular type camera, the F number is 2.8 to 8, and the exposure time is 1/30 to 1/30.
Despite the narrow range of 250 sec, it is shown that proper exposure can be obtained over the luminance range of Ev8 to Ev17 as in the conventional case.

The range indicated by P is the range controlled by the 7 otochromic substances. In this case, the element using 7-otochromic glass for the photographic lens was determined as shown in Fig. 1 (b) after various experiments.
), the front first element 21 . It has been found that when the front second element 22 has two elements and the intensity of the incident light exceeds a predetermined level, the average transmittance of the photographic lens is approximately inversely proportional to the intensity of the incident light. In this case, it goes without saying that instead of using photochromic glass, a film containing a substance whose transmittance changes in response to the subject light may be spread on the surfaces of the two front elements. do not have.

Figure 4 shows the exposure error and photographable range when photochromic glass is used in the photographing lens system of the above-mentioned simple camera.The solid line indicates high sensitivity and the average transmittance is approximately 1.
When using 7 otochromic glass saturated at 2%,
The dotted line shows the case using ordinary photochromic glass with low sensitivity.

ing. In this way, we were able to expand the photographic range by 3Ev compared to conventional cameras.

In addition, the element of the mark finder and the light receiving window for AF,
Similarly to the above, when using photochromic glass, it prevents the finder mark from becoming difficult to see when the subject becomes highly bright, and prevents the output of the AP light receiving section from saturating, thereby improving distance measurement accuracy. can be increased.

〔Effect of the invention〕

As explained above, the present invention uses an optical system as a component of the camera to control the electromechanical exposure of the camera by using an optical element to which a substance whose transmittance changes in response to the subject light is attached or mixed. Since it is possible to obtain proper exposure even for high brightness that exceeds the control range of the mechanism, the exposure control mechanism can be simplified and the camera can take pictures over a wide range of subject brightness. could be provided at an extremely low cost.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view showing an embodiment of the present invention, FIG. 1(b) is a diagram showing an example of a photographing optical system according to the present invention, and FIG. 2 shows a spectral transmittance curve of photochromic glass. Figure 3 is a diagram showing the exposure control curve when the present invention is implemented in a popular type camera, Figure 4 is a diagram showing the exposure error and possible shooting range when the present invention is implemented in a simple type camera, FIG. 5 is a diagram showing the exposure control curve of a conventional popular type camera, and FIG. 6 is a diagram showing the exposure error and photographable range of a conventional simple camera. ■...Camera body 2...Photographing lens 3...
・Finder 4...AF light receiving window 5...A
F light emitting window 21...front first element 22...'
Front second element

Claims (2)

[Claims] (1) A camera characterized in that an optical system as a component of the camera uses an optical element to which a substance whose transmittance changes in response to subject light is attached or mixed. (2) The camera according to claim 1, wherein the optical system is a photographing optical system.