US 4,047,190 AGranted

Hybrid exposure control system employing dual maximum blade displacement

AssigneePolaroid Corporation

InventorsBruce K. Johnson, George D. Whiteside

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Abstract

An exposure control system for photographic apparatus having a shutter-diaphragm mechanism for regulating the exposure aperture and the exposure interval under both ambient and flash illumination conditions. The shutter-diaphragm includes a blade arrangement which when driven in an opening direction provides enlarging aperture values in a tracking relation defining both a taking aperture and a photocell aperture until both achieve a maximum at which time further blade displacement provides a reduction in the photocell aperture to accommodate ambient, low scene light conditions. Under flash conditions, the system employs hybrid operation in which the exposure aperture is selected by a follow-focus mechanism in accordance with subject distance while the interval is determined by the scene light transmitted to the photocell. For large subject distances, the range of the follow-focus mechanism is restricted so as to limit the blade displacement to that at which both aperture values substantially achieve their maximum values.

Claims7

Dependent claims

A photographic camera comprising:

means for mounting photographic film material at a given film plane and for defining a given optical path along which image-carrying light rays may be transmitted to said film plane from the scene to be photographed;
means for defining a time interval responsive to the brightness of the scene;
means for unblocking and blocking said given optical path and for controlling said interval defining means, said unblocking and blocking means including means operative in a first range during unblocking of said given optical path for defining an aperture value progressively varying between a minimum and a maximum in operative relation to said given optical path and for controlling said interval defining means to vary the response thereof between minimum and maximum values and operative in a second range during unblocking of said given path for maintaining said aperture value at substantially said maximum value while reducing from its maximum value the response of said interval defining means to the scene brightness so as to accommodate low level scene brightness;
actuatable means for operating said unblocking and blocking means to unblock the given optical path and thereby initiate an exposure interval and, in response to said interval defining means, for subsequently operating said unblocking and blocking means to terminate said exposure interval;
means for selecting either ambient or artificial illumination operation of said camera;
and
means responsive to selection of said artificial illumination operation for precluding operation of said unblocking and blocking means in said second range and thereby preclude said reduction of response of said interval defining means during said artificial illumination operation.

4 more elements

A photographic exposure control system for a camera, said camera having means for mounting photographic film material at a given focal plane so as to receive image-carrying rays transmitted from the photographic scene along a given optical path, and means for selecting either ambient or artificial illumination operation, said system comprising:

means for sensing the brightness of the scene to be photographed;
a blade mechanism operative for unblocking and blocking at least said given optical path and for defining a primary aperture value in operative relation to said given optical path and a secondary aperture value in operative relation to said brightness sensing means, means for mounting said blade mechanism for displacement in a given direction between a first terminal arrangement wherein said blade mechanism is in blocking relation to at least said given optical path and a second terminal arrangement wherein said blade mechanism is in unblocking relation to both said given optical path and said sensing means, said blade mechanism defining primary and secondary aperture values progressively enlarging from a minimum to a maximum as said blade mechanism is displaced from said first terminal arrangement to a given blade arrangement just short of said second terminal arrangement and a reduced secondary aperture value as said blade mechanism is displaced from said given arrangement to said second terminal arrangement, said reduced secondary aperture value providing a reduction in brightness sensed by said sensing means so as to accommodate low light level brightness conditions of the photographic scene;
actuatable means operative in both ambient or artificial illumination operation for displacing said blade mechanism from its said first terminal arrangement toward its said second terminal arrangement to unblock said given optical path and initiate an exposure interval during which scene light is directed to the focal plane and, responsive to said scene brightness sensing means, for subsequently displacing said blade mechanism into a blocking arrangement to terminate the exposure interval;
and
means responsive to selection of said artificial illumination operation for precluding displacement of said blade member beyond said given blade arrangement.

2 more elements

Dependencies are inferred from the claim text.