Optar, a Method of Optical Automatic Ranging, as Applied to a Guidance Device for the Blind

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.