A simple deposition monitor has been incorporated into a thin‐film evaporator. The compact evaporator uses electron bombardment of the tip of a source wire to create an atomic beam. The current of ions in that portion of the atomic beam which falls on a collimating aperture is used to monitor the film deposition. The ion current is linearly related to the atomic beam flux, therefore allowing more precise control of the deposition rate than is obtained by monitoring the heating power delivered to the source wire. Calibration of the ion monitor within limits of ±6% requires positioning of the tip of the source wire within ±0.3 mm. This is readily accomplished using a plot of the current of bombarding electrons versus wire position. For the evaporation of iron, the calibration constant of this ion monitor is (2.50±0.15)×10−4ions/atom.