Archived posting to the Leica Users Group, 2003/03/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I'm no optical expert, but AFAIK, the "focus beyond infinity" has to do with heat expansion in telephoto lenses. If I recall correctly, heat causes the lens elements to shift ever so slightly (because of the metal in the barrel?) increasing the distance between the film plane and lens elemenst (same as focussing closer than infinity does). In normal lenses and short telephotos, this is not an issue, but in longer (and wider) teles, it means that "infinity" focus can be difficult to obtain (after all, "infinity" in lens design is only something like 1000x the focal length), so high quality, long telephoto SLR lenses can be focussed "beyond" infinity to allow for this. Since this is an SLR, you focus by sight (as opposed to a rangefinder), which means that if things look right in the viewfinder, they'll be fine on film. More knowledgable people will hopefully fill in the details/add corrections. A suitable net search will probably also help. M. - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html