US 4,303,318 AGranted

Camera exposure time control device

AssigneeMinolta Camera Kabushiki Kaisha

InventorsMashio Kitaura, Koji Yamamoto

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Abstract

An exposure time control device for a camera which measures the light reflected from a surface of a leading shutter curtain and/or a surface of a film can determine exact exposure time even if difference exists between reflection factors of the surfaces, by means of a simple construction including no special light measuring circuit other than a light measuring circuit originally provided for the exposure time control purpose. A first memory or storage capacitor memorizes logarithmically compressed output of the light measuring circuit fed through a first switch when the first switch is opened in conjunction with start of the leading shutter curtain travel while a second storage or memory capacitor memorizes the output fed through a second switch when the second switch is opened in conjunction with completion of the leading shutter curtain travel. An operational circuit combines the output of the light measuring circuit at a time of full shutter opening with the output in the second memory capacitor subtracted by the output in the first memory capacitor, producing a corrected output. A time count circuit controls timing of trailing shutter curtain release in accordance with the corrected signal.

In a camera which includes a focal plane shutter having leading and trailing shutter curtains for controlling the light reaching a film located at the focal plane of said camera, an exposure time control device comprising:

a light measuring circuit including light receiving means located to receive the light reflected from a surface of said leading shutter curtain before start of the travel of said leading shutter curtain, the light reflected from the surface of said leading shutter curtain and a surface of said film during the travel of said leading shutter curtain and the light reflected from the surface of said film after completion of the travel of said leading shutter curtain, said light measuring circuit generating a light measurement signal which is proportional to the logarithm of the intensity of said light received by said light receiving means;
first and second storing means for storing the light measurement signal from said light measuring circuit;
a first switch means arranged between said light measuring circuit and said first storing means for disconnecting said first storing means from said light measuring circuit in conjunction with the start of the travel of said leading shutter curtain;
a second switch means arranged between said light measuring circuit and said second storing means for disconnecting said second storing means from said light measuring circuit in conjunction with the completion of the travel of said leading shutter curtain;
an operational circuit having a first input terminal connected to said first storing means, a second input terminal connected to said second storing means and a third input terminal connected to said light measuring circuit, and generating a corrected signal by combining the light measurement signal to said third input terminal with the light measurement signal to said second input terminal subtracted by the light measurement signal to said first input terminal;
means for generating a shutter closing signal for actuating said shutter closing means when a period of time dependent on the corrected signal has lapsed from the start of the travel of said leading shutter curtain;
and electromagnetic means for starting the travel of said trailing shutter member in response to said shutter closing signal.

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Abstract

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