Abstract: An object carrier has a transparent plate with an opaque backing and carries a thin liquid crystal layer which, in turn, is covered with a 2 .mu.m glass plate carrying an object (microorganism, etc.). This carrier is placed in a microscope for photographic observation of the temperature-dependent reflectivity of the crystal layer as heat conductively coupled to the object. The average reflection of light by the crystal layer is used as a representation of its average temperature, to control backlighting of the opaque layer to, thereby, stabilize the average object temperature to at least 10.sup.-3 degrees centigrade.