> 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). Fred
