SLR camera with TTL exposure - has low loss resistance network for exposure factors

摘要

The SLR camera is fitted with a photocell to measure the exposure through the lens. For normal exposure control the illumination is measured with full aperture, and the output of the photocell, or its logarithmic value, is stored in the circuit memory. Other exposure factors are fed into the memory via a resistance network which is designed to take a minimum of power drain, so that impedance corrections do not have to be made when exposing through the set aperture. If the aperture is reduced to its selected value manual for focussing then the simulated aperture value, used with full aperture by means of a correction resistance, is automatically open circuited.