Exposure control circuit for camera of TTL reflective photometry type

Claim 1

An exposure control circuit for a camera of TTL reflective photometry type comprising a photoelectric transducer element for photometry, the transducer element receiving light from an object being photographed which passes through a taking lens and which is reflected by the surface of a first shutter blind and a film as the latter becomes exposed during running of the first blind to thereby produce a photocurrent in accordance with the brightness of the light; an amplifier having its inverting and non-inverting input terminals connected across the transducer element; an integrating capacitor to the non-inverting input terminal of the operational amplifier for integrating the photocurrent from the transducer element; a logarithmic compression semiconductor element connected across the inverting input terminal and the output terminal of the operational amplifier for converting the photocurrent from the transducer element into a logarithmically compressed voltage value; a correction semiconductor element connected across the non-inverting input terminal and the output terminal of the operational amplifier and adapted to conduct as the logarithmic compression element conducts to produce a correction current corresponding to the photocurrent from the transducer element; a control switch connected between the correction semiconductor element and the logarithmic compression semiconductor element and adapted to be opened in interlocked relationship with running of the first shutter blind to render the correction semiconductor element non-conductive; and a comparator for comparing a terminal voltage across the integrating capacitor against a given voltage level to produce an exposure terminal signal which allows a second shutter blind to run.