The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Dec. 01, 1987
Filed:
Dec. 09, 1986
Takanori Kohno, Tokyo, JP;
Copal Company Limited, Tokyo, JP;
Abstract
A control circuit for a programming shutter includes a light receiving element which is always exposed to light from a subject to be photographed and a logarithmic compression device which logarithmically compresses a photocurrent flowing through the light receiving element in accordance with the brightness of the subject. An output voltage of the logarithmic compression device is logarithmically expanded by a logarithmic expansion device and a logarithmically expanded current from the expansion device controls currents flowing through a plurality of weighted current sources. The currents flowing through the plurality of weighted current sources are added to or subtracted from a charged current to a condenser for integrating the brightness of the subject through a plurality of current switches corresponding to the current sources. On the other hand, shutter blades having the function of the diaphragm are opened in accordance with a predetermined opening characteristic in interlocked relationship with the shutter release operation and a counter is operated in interlocked relationship with the opening operation of the shutter blades. A count of the counter controls operation pattern of the current switches so that the charged current to the integrating condenser is conformed to the opening characteristic of the shutter blades. Further, a bias voltage for the logarithmic compression device is proportionated to an absolute temperature and is established to correspond to the film speed so that the parameter proportional to the absolute temperature is eliminated from the output current of the logarithmic expansion device.