An Electronically Controlled Additive Lamp House for Optical Printers

Abstract

The J-K Camera Engineering LH-3 additive lamp house employs closed-loop electronic control circuitry to regulate color balance and overall exposure for optical printers. The closed-loop control system automatically compensates for errors due to aging, dust accumulation, and manufacturing variations. Additive lamp house opto-mechanical design is simplified, resulting in lower costs. The electronic circuits have interfaces to allow control by an exernal computer. A dichroic mirror assembly is used to separate and recombine the three primary colors from three projection lamps. Neutral density wedges positioned by a motor are used to regulate overall exposure. Color is adjusted by varying voltage applied to the lamps by circuits which compare the light output intensity, measured with photosensors, to the desired intensity values, entered on switches or directly as input from a computer. Overall light is controlled in a similar manner, the light intensity being varied by the motorized wedges. The LH-3 utilizes linear scales for color and exposure values. Logarithmic scales may be converted to linear by straightforward calculations. When controlled by a computer, these conversions are made automatically, and the unit may be made to emulate any color and exposure system.