Abstract: A method and apparatus for normalizing the output of multiple light sources used to expose a photosensitive material to print high quality continuous tone and/or color images. Each of the multiple light sources is driven by a different signal weighted to cause all of the light sources to output light of intensity appropriate to produce a uniform image density over a wide range of image densities. In a preferred embodiment, each light source is driven by a different digital-to-analog converter (DAC) and/or timer circuit. A control processor supplies a multibit correction value tog each DAC and/or timer circuit to supply a drive signal to its associated light source weighted to cause all of the light sources to output light of substantially uniform intensity at a certain intensity level.

Abstract: A method and apparatus for measuring the linear movement between first and second substantially planar surfaces and is useful, for example, in an automatic focusing system of a photographic enlarging or printing machine. The linear movement between a first plane, e.g., a lens plane and a second plane, e.g., a film or print plane, at a single point, e.g., the lens optical center, is determined by measuring the linear movement of two diametrically opposed points proximate to the lens plane equidistant from the lens optical center. The two measured distances are then averaged to yield a distance measurement at the lens optical center corrected for any deflection of the lens plane.