Abstract: An adjustable sensor for detecting marks or "blips" on a strip of microfilm. The sensor includes a pair of individually adjustable sensing modules separately adjustably mounted on a mounting plate. Preferably the modules are magnetically mounted to the plate. Each sensing module includes magnet means and an electronic circuit encapsulated within a housing and an arm for adjusting the position of the housing on the mounting plate. A detector, preferably a fiber optic wand, is connected to the electronic circuit and partially encapsulated within the housing. The fiber optic wand extends outwardly of the housing to detect the blips on the microfilm.

Abstract: A system for optically detecting the presence of indicating markers on microfilm frames and for ignoring stray marks and smudges. As light shines through the microfilm and is detected by a photo-transistor, the system self regulates to provide an absolute baseline value, called a prescaler, for each frame of microfilm. Then, as each mark appears on the microfilm and interrupts the light path to the photo-transistor, the degree or extent of light blockage is measured as a deviation from the baseline for that frame. If the deviation exceeds a predetermined threshold, the mark is counted as a marker; otherwise the mark is ignored as a stray spot or smudge. The threshold is also self regulated based on a percentage of the amount that the light blockage of the marker in the immediately preceding frame deviated from the baseline for that frame.