Abstract An ellipsometer has been constructed for use in film growth studies which require a resolution of 0.01° and a nulling time on the order of 1 sec. The polarizer and analyzer are driven by stepping motors which may be stepped in either direction by pulses sent from the control system to the motor translator. The operating circuitry consists of a pair of bidirectional counters for recording the positions of the polarizer and analyzer, and a digital control system which sends pulses to the translators in the proper sequence to null the instrument. The data are printed on a digital printer and are plotted on an X- Y plotter during the course of an experiment. Data obtained in a study of the anodic oxidation of iron are presented to illustrate the performance of the instrument. The scatter in the data obtained using the instrument is comparable with its 0.01° resolution.