>>> I have read many times that the point of ininity changes with >>> temperature (and possibly other) variations, so all lenses focus >>> past infinity to allow for some movement in this point.
>> I'm not so sure about that. From my experience, generally only >> the longer telephotos (300mm and longer, usually) focus past >> infinity to allow for thermal changes. I believe that, for >> shorter lenses, the effects of heating and cooling are so small, >> and the DOF ample enough, that there is no need for focusing past >> infinity (and such a provision seems to be lacking in such >> lenses). > Fair enough, I cant say one way or the other knowledgably. > However, you talk about Dof being ample enough in WA lenses to > cover the innacurracy, so there must be some, and critical > focusssing using the scales has to be a gamble, even if only to a > small degree. I guess I'd have to agree with you there, Rob, to some extent. At least, I myself hardly ever use the distance scales for anything requiring any sort of reasonably critical focusing. However, this is partly (or maybe mostly) due to my usual lack of knowledge of the exact distance involved. (On the other hand, I do use the hyperfocal distance mark on the distance scale of a wide angle lens sometimes, when I'm shooting a scene at f/8 or f/11, but that is hardly a critical focus situation - <g>.) Fred
