Archived posting to the Leica Users Group, 1999/10/03
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]>> The Contax has, as you know, an electronic rather than mechanical >> rangefinder. > >How does an electronic rangefinder work? There's a discussion of electronic AF mechanisms (electronic rangefinders) in Norman Goldberg's book "Camera Technology - The Dark Side of the Lens". He explains it much better than I can. There are a couple of different kinds - moving prisms/mirrors with active IR projection and passive receptors are the two most popularly used types, and they're sometimes combined for even more accuracy in a wider range of illuminations. Both types use a comparator circuit: it essentially turns the received light into a frequency histogram which is used for matching until the best match is achieved. The AF used in SLRs is related to this technology, the sensor technology is different (more compact and designed to operate behind the main lens rather than in independent sensor windows) but the comparator principles are closely related. Godfrey