SINGLE LENS REFLEX CAMERA WITH CORRECTION FOR EFFECT OF STRAY LIGHT

• US 3,792,485 A
• Filed: 03/21/1973
• Issued: 02/12/1974
• Est. Priority Date: 03/21/1973
• Status: Expired due to Term

• Current Assignee: Karl-Peter Strauss
• Original Assignee: Karl-Peter Strauss
• Inventors: Strauss, Karl-Peter
• Primary Examiner(s): Peters, Jr., Joseph F.
• Application Number:
  US05/343,257
• Time in Patent Office: 328 Days
• Field of Search: 95/1C,1CE,1CT,1CD,42 352/141
• US Class Current: 396/245
• CPC Class Codes: G03B 7/085 for control of aperture

Abstract

A single lens reflex camera in which one of the exposure factors (diaphragm aperture or shutter speed) is automatically set by means responsive to the light from the scene to be photographed. The photoelectric converter which receives light from the scene, is subject also to the influence of possible stray light. A circuit arrangement is provided for storing the voltage produced by the stray light falling on the photoelectric converter. Then when the light from the scene to be photographed falls on the photoelectric converter, only the excess of the voltage then produced by stray light plus scene light, over the previously stored voltage produced by the stray light alone, is used in setting the automatically settable exposure factor, thereby compensating for the effect of stray light.

Claims

1. A single lens reflex camera with an objective shutter, a photoelectric converter receiving light from a scene to be photographed, through said shutter when the shutter is open, and receiving stray light both when the shutter is open and when it is closed and having an output depending upon the light received, exposure factor regulating means having an input derived in part from an output of said converter, a storage element, switch means open when said shutter is open and closed when said shutter is closed, and circuit means including said converter, said storage element, and said switch means for impressing on said storage element a threshold value dependent on the output of said converter when subjected to the effect of only stray light on said converter while said shutter is closed, said circuit means simultaneously providing zero input to said regulating means, said circuit means also serving, when said shutter is open and said converter receives both stray light and scene light, to provide to said regulating means an input dependent on the amount by which the then output of said converter exceeds said threshold value previously impressed on said storage element, so that the input then supplied to said exposure factor regulating means is substantially independent of the effect of stray light on said photoelectric converter.

2. A photographic camera comprising shutter means, diaphragm aperture setting means, light sensitive means subject to stray light when the shutter means is closed and subject when the shutter means is open to stray light plus scene light from a scene to be photographed, said light sensitive means having an output varying according to the amount of light falling upon it, and operating means responsive to the difference in output of said light sensitive means when the shutter means is closed and when the shutter means is open for operating said aperture setting means in accordance with such difference.

3. A construction as defined in claim 2, wherein said camera is a single lens reflex camera, said light sensitive means includes a photoelectric converter, and said operating means includes a capacitor for storing a charge proportional to the stray light output of said converter when said shutter means is closed and a switch closed when said shutter means is closed and open when said shutter means is open, said switch when closed serving to prevent any output of said converter and any charge on said capacitor from influencing said aperture setting means and serving when open to connect said converter and said capacitor operatively to said aperture setting means.

4. A construction as defined in claim 2, wherein said light sensitive means includes a photoelectric converter, and said operating means includes a capacitor charged by the output of said converter, and wherein said shutter means has an operating cycle during which, prior to making an exposure, the shutter means is momentarily closed so that said capacitor will be charged to a threshold value by the output of said converter when subjected only to stray light, and the shutter means will then be opened so that said converter will have an output responsive to scene light plus stray light, said operating means being responsive only to the amount by which the output of said converter exceeds the previously measured threshold value.

5. A construction as defined in claim 1, wherein said circuit means includes a film speed potentiometer and a shutter speed setting potentiometer.

6. A construction as defined in claim 1, wherein the exposure factor regulating means regulates the factor of diaphragm aperture.

7. A construction as defined in claim 1, wherein the exposure factor regulating means regulates the factor of shutter speed.