1978-05-30
1979-06-19
Gellner, Michael L.
354 32, 354 51, 354 60F, 354139, G03B 708, G03B 1505
Patent
active
041584929
ABSTRACT:
A light responsive circuit adapted to measure natural or ambient light and artificial light such as from an electronic flash device, includes a photocell, a logarithmic compression circuit for generating a first output proportional to the logarithm of the light intensity incident on the photocell, a calculation circuit for adding to or subtracting from the first output an electric quantity, such as voltage, which is determined in accordance with a light unrelated input, for example, a film sensitivity setting, thereby generating a second output as a result of the addition or subtraction, a logarithmic expansion circuit for generating a third output proportional to the anti-logarithm of the second output, and an operating circuit responsive to the third output for controlling or indicating at least one camera exposure factor. The light responsive circuit according to the present invention is characterized in that a first control circuit controls or shifts the level of the second output for the same input, in accordance with the light to be measured; and a second control circuit controls the operation of the operating circuit in accordance with the light to be measured, whereby linearity of the logarithmic expansion characteristic is ensured due to the shift of the range of the second output to accommodate the extremely high intensity of the flash light.
REFERENCES:
patent: 4016575 (1977-04-01), Uchiyama et al.
patent: 4078242 (1978-03-01), Uchiyama et al.
Kitaura Mashio
Taniguchi Nobuyuki
Gellner Michael L.
Minolta Camera Kabushiki Kaisha
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