Diaphragm control device for cameras
AssigneeMinolta Camera Kabushiki Kaisha
InventorTokuji Ishida
Life of this patent
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Abstract
A diaphragm control device of the type which performs TTL light measurement while stopping-down a diaphragm is constructed to automatically determine the diaphragm aperture by comparing an approximate signal with a reference signal to minimize the diaphragm aperture determination error caused when timewise variations are involved in the scene brightness. The approximate signal is generated by various circuits on the basis of a light measurement signal obtained by the TTL light measurement. The approximate signal varies approximately with the change in the diaphragm aperture due to the stopping-down operation of the diaphragm and coincides with the light measurement signal when no timewise variations are involved in the scene brightness.
Claims12
A diaphragm control device for a camera which includes a diaphragm forming a diaphragm aperture and which is capable of a stopping-down operation and a means for initiating the stopping-down operation of said diaphragm, said control device comprising:
- a light measuring circuit for generating a light measurement signal commensurate with the scene brightness measured through said diaphragm aperture, said light measurement signal including fluctuation components when timewise variations are involved in the scene brightness and which varies with the change in said diaphragm aperture due to the stopping-down operation of said diaphragm;
- an approximate signal-generating circuit for generating, on the basis of said light measurement signal, an approximate signal which varies approximately with the change in said diaphragm aperture due to the stopping-down operation of said diaphragm and which coincides with said light measurement signal when no fluctuation components are included in said light measurement signal;
- means for generating a reference signal;
- and
- stopping-down operation stopping means for stopping the stopping-down operation of said diaphragm when said approximate signal represents a given relationship with respect to said reference signal.
A camera comprising:
- a diaphragm forming a diaphragm aperture and capable of stopping-down operation:
- means for initiating the stopping-down operation of said diaphragm;
- a light measuring circuit for generating a light measurement signal commensurate with the scene brightness measured through said diaphragm aperture, said light measurement signal including fluctuation components when timewise variations are involved in the scene brightness and varying with the change in said diaphragm aperture due to the stopping-down operation of said diaphragm;
- an approximate signal generating circuit for generating, on the basis of said light measurement signal, an approximate signal which varies approximately with the change in said diaphragm aperture due to the stopping-down operation of said diaphragm and which coincides with said light measurement signal when no fluctuation components are involved in said light measurement signal;
- means for generating a reference signal;
- stopping-down operation stopping means for stopping the stopping-down operation of said diaphragm when said approximate signal represents a given relationship with respect to said reference signal;
- means for latching said approximate signal in response to the actuation of said stopping-down operation stopping means;
- and
- means for controlling an exposure time in accordance with said approximate signal latched by said latching means.
Dependencies are inferred from the claim text.