A microdensitometer is described that has the form of an attachment fitting over the ocular tube of a standard microscope. It periodically scans a stationary object which can be viewed at the same time by the eye. The electrical output of the densitometer is displayed on an oscilloscope screen, with linear or logarithmic readout. Maximum resolution is 1 micron using a 20× N.A.0.5 microscope objective. Measurements can be made of photographic films and of electron beam spots on fluorescent screens without modifying the instrument.