The development of a high-quality 35-mm film scanner

A review of the known methods of scanning film leads to the choice of a cathode-ray-tube flying-spot method, with continuously moving film and twin optical systems selected alternately by a mechanical shutter. This system is examined to assess the magnitude of factors likely to influence the performance, with particular reference to accuracy of scanning and registration of alternate frames, mechanical steadiness, definition, contrast characteristics and signal/noise ratio. A detailed description is given of the more important features of the design. Optical and mechanical features include the folded double optical system, the shutter, the automatic correction for film shrinkage, the mechanical filter for stabilization of film velocity, the servo control of the phase of the non-synchronous driving motor and the use of separately driven take-up spools. The main vision chain is described with particular reference to after-glow effects and corrections, low-noise first amplifier, correction of phase distortion, gamma correction and stabilization of black level.