Since before World War II, optical comparators have been a staple in large factories and small shops, and in industries as diverse as automotive and health care. Their basic uses have re-mained the same, even as the machines have evolved to include digital readouts, mechanized travel, sophisticated software, quick change bayonet lenses or lens turets, edge detection capabilities and improved optics and lighting. Whether the operator measures small, lightweight, flat parts with a vertical projector, or heavier, round parts on a horizontal machine, the comparator still projects a magnified shadow of a part's contour onto a precision-ground glass screen for comparison.
"The optical comparator is still a workhorse in the industry," said Mike Metzgar, department manager of measuring systems at Nikon (Melville, NY). "They are so easy to use that anybody with some real basic training can walk up to a comparator and measure a part or a feature."