Abstract: A scanning electron microscope or other type of scanning electron device incorporating a light pen for automatically changing the field of view of a specimen on a CRT. The output of said light pen controls the center and/or width of the scanning area of the incident electron beam irradiating the specimen when said light pen is directed towards a certain point in the initial specimen field of view on the CRT, thereby displaying said point at the center of the changed field of view on the CRT.

Abstract: A constant temperature heater includes a thermistor having a positive temperature coefficient and a varistor stacked upon one another in an electrically insulating casing in such a manner that the thermistor and varistor are electrically connected in series with each other and the thermistor is in heat exchange relationship with a radiator plate on the casing. A spring in the casing presses the varistor and thermistor into firm engagement with each other and biases the thermistor into good heat conductive relation with the radiator plate. The varistor serves to reduce the transient currents in the thermistor and reduces the heat dissipation power of the thermistor, thereby providing a longer service life.

Abstract: A film handling system to with which a film cartridge is commonly usable in each step of exposure, processing (developing) and projection of the film housed therein, wherein a safety means which advances the above mentioned film cartridge through each step in which it is used in a prescribed sequence is provided. Further an electric circuit which controls the above mentioned handling system in such manner as to activate said system according to the output of the safety means is provided so that such erroneous handling as occurs when processing or projecting unexposed film by mistake or by projecting unprocessed film can be automatically prevented.