Optical System of a Sensitometer with a High Range of Non-selective Light Modulation

Reasons for non-selective light modulation in a sensitometer for fundamental research in sensitometry are discussed, particularly with respect to high-range modulation. The underlying optical system described in this paper essentially involves multi-element flat mechanical modulators placed in between light channels of rectangular cross section. A modulator may, with advantage, be constructed in such a way that the outgoing flux changes exponentially with some linear movement, full-scale translation corresponding to exactly one order of magnitude. The number of modulators and light channels used defines the total range of modulation. Using a 650 watt halogen lamp in the illuminating system it is possible to obtain, within the range 1 : 6, 50 000 Lx of light output level with a uniformity better than 2 per cent. Finally, some results measured with the prototype of the instrument are given.