Application of digital light processor systems in monochromator, spectrophotometer or the like systems to mediate selection of individual wavelengths, andor to image elected regions of a sample in an imaging ellipsometer, imaging polarimeter, imaging reflectometer, imaging spectrophotometer, andor to provide chopped beams. The cross-section profile of the shaft of the gun is rhomboid, tapered from the centre towards the two ends. The lower portion may have a skirt portion which has a non-linear upper peripheral edge. A generating unit generates a probability distribution function of the characteristic parameter for each of the possible binary values for the memory cell collection. Finally, a retainer device is positioned for removably securing the pressure responsive element and bias force exerting mechanism within the passageway.