GB850495A - Improvements relating to photographic methods - Google Patents

Abstract

850,495. Photo-electric exposure control. LOGETRONICS Inc. June 17, 1958 [June 17, 1957], No. 19302/58. Class 40(3). In a photographic method each elemental area of the subject is illuminated by a spot of light from a cathode-ray tube for a dwell period proportional to the light directed from that area to a photo-sensitive printing surface, and at the termination of each dwell period the spot is shifted to illuminate the next area until each elemental area of the subject has been printed. Light is directed from the C.R.T. 20 through an elemental area of the negative 28 to the printing surface 34. Part of this light is directed by a partial mirror 32 to a photo-cell 36. The output current of the cell is applied via an amplifier 38 to an integrator 42 the output of which is compared in comparator 46 with a reference voltage supplied by the unit 44. When the reference voltage is exceeded the generator 48 produces a pulse which momentarily blanks the CRT, discharges the integrator circuit and triggers the horizontal step function generator 52 which steps the spot to the next elemental area, at the end of each scanned row the end exposure blanking circuit 62 blanks the light beam and the vertical step function generator 54 steps the spot one elemental area vertically and the next horizontal scanning cycle commences. The reference voltage determines the exposure which is constant for each area. Specification 790,509 is referred to.