Photometric system

A photometric apparatus for use in an image pick-up device comprising a light receiver arranged at a focal plane of a camera lens optical system for receiving an image focussed by the camera lens optical system;

• a reference light quantity setting and generating circuit connected to the light receiver for generating a reference light quantity by obtaining a mean value between a maximum value and a minimum value of the amplitude of the luminance signals from the light receiver;
• a logarithmic compression circuit connected to the light receiver for logarithmically compressing the luminance signals from the receiver;
• a window comparator circuit connected to the logarithmic compression circuit and the reference light quantity setting and generating circuit for selecting luminance signals of amplitude having a value within a range of predetermined exposure value;
• a signal treating circuit connected to the window comparator circuit and the logarithmic compression circuit for treating the signals from these circuits to obtain an average value of the amplitude of the luminance signals selected by said window comparator circuit in relation to the reference light quantity set in the reference light quantity setting and generating circuit;
• an information circuit for generating signals of exposure factors;
• an arithmetic circuit connected to the signal treating circuit and the information circuit for calculating the mean value output of the signal treating circuit and the exposure factors of the information circuit;
• a control device connected to the arithmetic circuit for controlling the shutter speed and the iris of the image pick-up device;
• and a display device connected to the arithmetic circuit for displaying the shutter speed value and the iris value of the image pick-up device.