Exposure control system having dual mode photodetector

• US 4,632,542 A
• Filed: 05/02/1985
• Issued: 12/30/1986
• Est. Priority Date: 05/02/1985
• Status: Expired due to Term

• Current Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Original Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Inventors: Whiteside, George D.
• Primary Examiner(s): ADAMS JR, RUSSELL E
• Application Number:
  US06/729,989
• Time in Patent Office: 607 Days
• Field of Search: 354/419, 354/481
• US Class Current: 396/65
• CPC Class Codes: G03B 7/09979 Multi-zone light measuring

Abstract

An exposure control system for a photographic camera of the type employing a scanning type shutter, a controllable source of artificial illumination and a photodetector for sensing scene brightness levels both prior to and during film exposure preferably includes a light diffuser that is automatically movable, in response to a selected camera function, between a first position where it can collect scene radiation from a field of view substantially greater than that of the photodetector and then direct the collected radiation along an optical path onto the light sensitive surface of the photodetector, and a second position displaced from the photodetector where the diffuser has no effect on the amount of scene light measured by the photodetector. Scene brightness level is normally measured before actual film exposure in order to determine the amount of artificial illumination that must subsequently be added to the scene during film exposure and is measured during film exposure to control the extent of shutter blade opening for proper film exposure. By increasing the effective size of the viewing angle over which scene brightness level is measured prior to exposure, the photodetector is precluded from classifying an otherwise low light level scene as a high light level scene if a relatively bright, but localized light source should be present in the scene to be photographed, thereby avoiding the possibility of an underexposed photographic image being caused by such a localized light source.

Claims

1. In an exposure control system for a camera having an adjustable focus objective lens and adapted to control the amount of light from a scene incident upon photosensitive film during exposure sequences, the improvement comprising:

means for evaluating scene light including a photodetector system having an acceptance angle, a photosensitive surface for providing an electrical output signal that varies in accordance with the amount of radiant energy incident on said photosensitive surface and an optical system for collecting scene light within a particular acceptance angle and for directing said collected light onto said photosensitive surface;

means for adjusting said photodetector system between a first arrangement and a second arrangement wherein its said acceptance angle differs from that in its said first arrangement including a diffuser movably mounted between a first position where it increases the size of said acceptance angle and a second position where it does not change the size of said acceptance angle and means coupling said objective lens to said diffuser for moving said diffuser between its said first and second positions in response to objective lens focusing movement to thereby change the acceptance angle of said photodetector system;

means for making a pre-exposure evaluation of scene light utilizing said diffuser in its said first position and for then subsequently making an evaluation of scene light while the photosensitive film is being exposed to scene light utilizing said diffuser in its said second position and producing a control signal responsive thereto; and

means responsive to said pre-exposure evaluation of scene light for providing either for selecting one of a plurality of alternately available operational exposure parameters during an exposure sequence of said camera and further responsive to said control signal for terminating the exposure of the photosensitive film to scene light.

2. In an exposure control system for a camera having an adjustable focus objective lens and adapted to control the amount of light from a scene incident upon photosensitive film during exposure sequences in both high ambient and low ambient scene light conditions, the improvement comprising:

means for evaluating scene light including a photodetector system having an acceptance angle, a photosensitive surface for providing an electrical output signal that varies in accordance with the amount of radiant energy incident on said photosensitive surface and an optical system for collecting scene light within a particular acceptance angle and for directing said collected light onto said photosensitive surface, said optical system including a lens movably mounted between a first position where it establishes a first photodetector acceptance angle and a second position where it establishes a second photodetector acceptance angle;

means for adjusting said photodetector system between a first arrangement wherein its said acceptance angle is substantially less than that of the camera'"'"'s objective lens and a second arrangement wherein its said acceptance angle is significantly larger than that in its said first arrangement including means coupling said objective lens to said photodetector lens for moving said photodetector lens between its said first and second positions in response to objective lens focusing movement to thereby change the acceptance angle of said photodetector system;

means for making a pre-exposure evaluation of scene light utilizing said photodetector system in its said second arrangement, said second arrangement of said photodetector system serving to reduce the contribution of light from a small bright source during said pre-exposure evaluation, and producing a first output signal in response to a low level of scene light and a second output signal in response to a high level of scene light, and for then subsequently making an evaluation of scene light while the photosensitive film is being exposed to scene light utilizing said photodetector system in its said first arrangement and producing a control signal responsive thereto; and

means responsive to the presence of either said first or second output signals during said pre-exposure evaluation of scene light for respectively providing either a first or second selection of operational exposure parameters during an exposure sequence of said camera and further responsive to said control signal for terminating the exposure of the photosensitive film to scene light.

3. In an exposure control system for a camera having an adjustable focus objective lens and adapted to control the amount of light from a scene incident upon photosensitive film during exposure sequences in both high ambient and low ambient scene light conditions, the improvement comprising:

means for evaluating scene light including a photodetector system having an acceptance angle, a photosensitive surface for providing an electrical output signal that varies in accordance with the amount of radiant energy incident on said photosensitive surface and an optical system for collecting scene light within a particular acceptance angle and for directing said collected light onto said photosensitive surface;

means for adjusting said photodetector system between a first arrangement wherein its said acceptance angle is substantially less than that of the camera'"'"'s objective lens and a second arrangement wherein its said acceptance angle is significantly larger than that in its said first arrangement including a diffuser movably mounted between a first position where it increases the size of said acceptance angle and a second position where it does not change the size of said acceptance angle and means coupling said objective lens to said diffuser for moving said diffuser between its said first and second positions in response to objective lens focusing movement to thereby change the acceptance angle of said photodetector system;

means for making a pre-exposure evaluation of scene light utilizing said photodetector system in its said second arrangement, said second arrangement of said photodetector system serving to reduce the contribution of light from a small bright source during said pre-exposure evaluation, and producing a first output signal in response to a low level of scene light and a second output signal in response to a high level of scene light, and for then subsequently making an evaluation of scene light while the photosensitive film is being exposed to scene light utilizing said photodetector system in its said first arrangement and producing a control signal responsive thereto; and

means responsive to the presence of either said first or second output signals during said pre-exposure evaluation of scene light for respectively providing either a first or second selection of operational exposure parameters during an exposure sequence of said camera and further responsive to said control signal for terminating the exposure of the photosensitive film to scene light.

4. In an exposure control system for a camera having and adjustable focus objective lens and adapted to control the amount of light from a scene incident upon photosensitive film during exposure sequences, the improvement comprising:

means for evaluating scene light including a photodetector system having an acceptance angle, a photosensitive surface for providing an electrical output signal that varies in accordance with the amount of radiant energy incident on said photosensitive surface and an optical system for collecting scene light within a particular acceptance angle and for directing said collected light onto said photosensitive surface, said optical system including a lens movably mounted between a first position where it establishes a first photodetector acceptance angle and a second position where it establishes a second photodetector acceptance angle;

means for making a pre-exposure evaluation of scene light utilizing said photodetector system in its said first position and for then subsequently making an evaluation of scene light while the photosensitive film is being exposed to scene light utilizing said photodetector system in its said second position and producing a control signal responsive thereto;

means responsive to said pre-exposure evaluation of scene light for providing either for selecting one of a plurality of alternately available operational exposure parameters during an exposure sequence of said camera and further responsive to said control signal for terminating the exposure of the photosensitive film to scene light; and

means coupling said objective lens to said photodetector lens for moving said photodetector lens between its said first and second positions in response to objective lens focusing movement to thereby change the acceptance angle of said photodetector system.