Photographic system with slow burn flash bulb

• US 4,444,479 A
• Filed: 01/27/1982
• Issued: 04/24/1984
• Est. Priority Date: 01/05/1981
• Status: Expired due to Fees

• Current Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Original Assignee: Polaroid Corporation (PLR IP Holdings LLC)
• Inventors: Johnson, Bruce K., Whiteside, George D.
• Primary Examiner(s): ADAMS JR, RUSSELL E
• Application Number:
  US06/343,160
• Time in Patent Office: 818 Days
• Field of Search: 354/27, 354/33, 354/137, 354/138, 354/173
• US Class Current: 396/168
• CPC Class Codes: G03B 15/04 Combinations of cameras with non-electronic flash apparatus; Non-electronic flash units

Abstract

A photographic system for minimizing exposure tracking error under flash illumination using a low-cost camera in which an automatic shutter system constitutes the sole control of exposure illumination passed to the film. The source of flash illumination is a low-cost filament vaporizable flash bulb in which the effective burn time is increased without change in total illumination energy to the maximum interval of exposure time compatible with hand-held camera operation. The reduced maximum intensity and lengthened burn time reduces the proportionate amount of exposure illumination during shutter closing movement and, consequently, the deleterious effect of variation in shutter closing movement so that exposure with varying camera/subject distances and flash illumination is relatively unaffected.

Claims

1. A photographic system for exposure of film having a fast film speed, said system comprising:

a camera having an objective lens adequate to yield a range of camera/subject distances extending from a minimum focus distance and within such range the image of a subject is focused at a film plane defined by the camera;

a shutter operable between an open condition defining a fixed exposure aperture to pass light from said lens to said film plane and a closed condition to block such passage of light, said shutter constituting the sole means for determining light to which the film is exposed;

means responsive to initiation of a camera cycle for actuating said shutter to its said open condition;

means for generating a shutter closing signal in response to scene light including an anticipation circuit to advance the time of said shutter closing signal in accordance with increased scene illumination;

means responsive to said shutter closing signal for moving said shutter from said open condition to said closed condition during a definite interval of shutter closing time;

a vaporizable filament flashbulb mounted on said camera,

said flash bulb producing illumination of a fixed amount limited to provide proper exposure of light sensitive film at said film plane for a predetermined maximum camera/subject flash distance and having an intensity of illumination variable with time between minimum and maximum values, said flash bulb having an extended burn time, measured between the rise and fall of the intensity to approximately one-half said maximum value, substantially equal to the longest interval of time compatible with hand-held camera operation; and

means for energizing said flash bulb in fixed relation to opening said shutter to said fixed aperture and so that said interval of shutter closing time occurs exclusively during said extended burn time for camera/subject distances between said minimum focus distance and said predetermined maximum camera/subject flash distance, to thereby maximize the exposure time for said given aperture for each subject distance and reduce the proportionate amount of flash illumination passed to the film plane during the closing interval while maintaining flash bulb efficiency.

2. The system of claim 1 in which said burn time of said source of flash illumination is approximately 20 milliseconds.

3. A photographic system for exposure of film having a fast film speed, said system comprising:

a camera having an objective lens adequate to yield a range of camera/subject distances extending from a minimum focus distance and within such range the image of a subject is focused at a film plane defined by the camera;

means for defining a given aperture including a shutter operable between a full-open condition at said given aperture to pass light from said lens to said film plane and a closed condition to block such passage of light;

means responsive to initiation of an exposure cycle for actuating said shutter to its open condition;

a vaporizable filament flash bulb mounted on said camera, said flash bulb having a fixed energy of illumination limited to provide proper exposure of the film at said given aperture for a predetermined maximum camera/subject flash distance and having an intensity of illumination variable with time between minimum and maximum values, said flash bulb having an extended burn time, measured between the rise and fall of the intensity to approximately one-half said maximum value, substantially equal to the longest interval of time compatible with handheld camera operation;

means for generating a shutter closing signal in response to scene light, including light reflected to the camera from the subject to be photographed, said signal generating means including an anticipation circuit to advance the time of said shutter closing signal in accordance with increased scene illumination;

means responsive to said signal for moving said shutter from said full-open condition to said closed condition during a definite interval of shutter closing time; and

means for energizing said flash bulb solely at said given aperture upon movement of said shutter to said full-open condition and so that said interval of shutter closing time occurs exclusively during said extended burn time for camera/subject distances between said minimum focus distance and said predetermined maximum camera/subject flash distance, to thereby maximize the exposure time for said given aperture for each subject distance and reduce the proportionate amount of flash illumination passed to the film plane during the closing interval while flash efficiency is maintained.

4. The apparatus of claim 3 wherein said maximum aperture is in the range of from f/19 to f/27.

5. The apparatus of claim 3 wherein said fixed energy of illumination is on the order of 325 zonal lumen seconds.

6. The apparatus of claim 3 wherein said burn time is substantially 20 milliseconds.