Exposure control system stabilized against temperature variation

摘要

An exposure control system for a camera capable of deriving more reliable and accurate exposure values over an extended range of scene luminance despite variation of the ambient temperature of the system than was previously possible. The exposure control system is characterized by the use of a photovoltaic cell and a logarithmic converter connected thereto in combination with a voltage stabilizer for providing output current signals of which the values are independent of temperature to the automatic camera diaphragm aperture regulating mechanism. The logarithmic converter consists of an operational amplifier with a feedback diode connected between the input and the output of the operational amplifier. The voltage stabilizer connected to the operational amplifier comprises a plurality of transistors selected to have such characteristics that the temperature dependance components of the luminance versus output signal response characteristic of the photovoltaic cell and the logarithmic conversion of the converter are cancelled by the temperature dependence component of the voltage supplied from the voltage stabilizer.