Archived posting to the Leica Users Group, 1997/11/08
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]In message <199711050458.XAA23683@s1-bngr.agate.net> Jack Milton writes: > The exotic glasses used in apochromatic telephotos can expand and > contract (at least this is how it was explained to me) causing infinity > focus to vary according to temperature. It is nothing to worry about and > usually in fast telephoto lenses you'll notice that there is some focus > travel past the infinity mark possible to account for such variations. Not just that - all kinds of thermal variations plus the possibility of a minor knock affecting the infinity setting, etc. Most serious professional lenses focus past infinity - but it's usual for this also to be shown on the scales. An indicated 'infinity' _should_ be infinity - but the mount should go just past that point. - -- Phil Payne