In an electronic still camera adapted for professional or amateur photography, a solid state thermo-electric cooler rapidly cools a solid state image sensor (imager) in accordance with the ambient illumination or subject brightness, so as to rapidly increase the sensitivity of the imager to the required level. Thus, the device may be used in place of a flash attachment for still photography under low-light conditions. A microprocessor controls the cooler and determines optimum imager temperature for a given set of subject brightness, shutter speed and aperture size values. These values are correlated to corresponding optimum imager temperatures by a set of polynomials--or by a set of look-up tables--stored in a read only memory accessed by the microprocessor.