Monday, November 14

Camera Alignment

In the bad old days of tube cameras, line-up was a daily (or more frequent) requirement. The camera tubes were thermionic devices which drifted constantly, as did the analogue circuitry that controlled them. So, we had to look after beam current, beam focus, raster geometry, registration, all before even starting on the camera chain controls. These front end alignments had to be carried out by a highly skilled Engineer. They were not operational tweaks. The same Engineer would then proceed to set up the subsequent chain, adjusting blanking, flares, shading, blacks, gains, gammas, linear matrix, clippers, knees, contours, thresholds, coring and more. When solid state image sensors appeared and matured, the front end alignments no longer applied. There was no scanning beam and the devices, being physical, had fixed geometry. In practice, they were instruments for measuring the aberrations of the lens. Also the digital camera chains were far more stable than their analogue predecessors. The net effect of these improvements was to reduce Engineering intervention. Unfortunately, in some cases intervention has been reduced almost to zero. It is unfortunate because to get good matching pictures from modern cameras there are still a few controls that have to be optimised regularly. Let's see. These include: flares, shading, blacks, gains, gammas, linear matrix, clippers, knees, contours, thresholds, coring and more. Familiar list? Plus ├ža change...