Moose wrote:
> A true zoom holds focus from wide to long, but usually gives finest
> focus is at the long end 'cause either eye or focus sensor can see to
> focus more precisely with the enlarged image. The change you see may
> simply be from less than perfect focus at the short end. It is not
> uncommon for people concerned with MF focus to focus at the long end,
> then zoom back to frame the subject.
I used this technique quite often with the 35-70/f4 Zuiko.
> Many complex zooms focus past infinity at normal temperatures so that
> they can focus all the way there at extreme(s). Mirror lenses too.
Didn't know this. Thanks for the education. :)
> It is easier to design and cheaper to make a varifocal lens, one that
> changes focal length, but doesn't maintain perfect focus as it does so.
> A few of these were made in the MF era. It is possible that makers of AF
> zooms cheat a little, as the AF doesn't care. I'm not accusing Oly of
> this, only speculating about all makers. The temptation to make this
> compromise to get smaller, lighter, cheaper lenses with equal optical
> performance must be considerable in a competitive market where almost
> no-one manually focuses AF zooms.
The Zuiko Digital 14-54 behaves in this fashion in that it doesn't
maintain focus as you change zoom settings. I'm one of those "no-ones"
that uses manual focus quite often. I've got the E-1 set so the AEL
button activates auto-focus and thus, is removed from the shutter
button. I set the camera to manual focus, use the AEL button to
initially set focus and then manually focus the lens to fine tune.
Works for landscape images quite nicely. :)
Richard L
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