Why “Telecentric Range” is a misleading concept?
Some suppliers talk about a supposed “telecentric range”, that is to say that within a certain depth range (expressed in mm) the maximum error you would get would stay within a certain amount (usually expressed in micron); this parameter is somewhat meaningless from an optical point of view and possibly misleading. Incoming ray cones show a maximum inclination expressed in degree which depends on the lens telecentricity. Since rays “run straight” in space, let’s say that “all the space is telecentric”! We guarantee our lenses to have a maximum telecentric slope of 0.1°, 0,0017 (1.7 mrad) if turned into radians, although the typical departure from perfect telecentricity in tests is usually half of that, about 0,0008 rad (0.8 mrad). This means that the maximum error for a displacement of 1 mm would be less than 1 micron. A crucial difference between us and our competitors is that, while they just state a value for telecentricity, we do measure that parameter with specific test instrument
