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Optical automatic devices, using ambient light only, can locate and range objects up to about 100 feet. Shallow real images of the objects are formed by a wide-aperture lens in an image space where a moving vane with minute bars and slots periodically cuts across all light rays in one image plane after another. Whenever the bars coincide with a sharp image they modulate the light received by a photocell. Range information may be read on a meter or control directly a range-following servo mechanism. A small hand-held guidance device for the blind is described. It is used for probing like a flashlight but operates on ambient light when that exceeds one foot-candle. Image space is explored several times per second by a helical vane with bars spaced the closer the nearer the objects whose image they intercept. A photo-multiplier and audio amplifier feed the resulting whistle-modulation to an earphone, 8 frequencies corresponding to 8 ranges from 20 inches to 20 feet. A motor turns the vane, also a chopper to supply via transformer and twentyfold voltage multiplier 1000 volts dc to the electron multiplier; total consumption is 50 ma from one 1.5v cell. , pp. 102-105; April, 1950.