Graywolf wrote: > The stop may not be infinity but the mark should be. My Graphic focuses past > infinity, that does not mean i can not set it there. Also anything between > infinity and the hyperfocal distance should be sharp so you probably only have > to be within a quarter turn of the focus ring. > > I notice in other comments to this thread that people seem to be blaming all > kinds of other problems on focus. Out of focus is out of focus. Soft do to mist > on the lens is soft. Vibration do to inadequate tripods and heads are motion. > Only poor focus is a focus problem and there is no, none whatsoever, excuse for > that when the subject is at infinity (600+ X the focal length).
Lens manufacturers don't allow the focus ring to go beyond infinity mark to fool photographers. It's because with long lenses even normal temperature changes can shift the actual infinity position enough for getting out of focus pictures. Hence true infinity focusing can be everywhere "around" infinity mark, not necessarily on it. For this reason, when focusing at infinity with long telephoto, telescopes and so on, you have to carefully check infinity focus just like you do with any other focusing distance: by looking at image in the viewfinder! BTW, this is why the SLR is the best camera for astrophotography (and not only for that). With other cameras, the only way to get proper focus is to check at film plane. Dario (who shot astrophotography for years, long time ago...)
