Abstract: A heater assembly for microscope objectives is disclosed. The assembly includes a loop-shaped flexible heating element sized and constructed to surround and operatively engage microscope objectives of different sizes. The heating element is fixed to a rigid housing. A thermistor is fixed in one end section of a slidable, tubular member arranged with the housing to translate towards and away and into and out of engagement of the thermistor with microscope objectives. Electrical conducting wiring connects the heating element and thermistor with a controllable heat energy for regulating the heat energy source to the microscope objective. The housing also supports a lock screw for securing the tubular member with the housing.