First, make sure you are looking at an object far enough away to
really be at an infinity focus point. With a long lens (>200mm),
this will be .5 to 1 mile. With some of my long lenses, the focus is
before the infinity mark on the lens. This is common on long lenses
so there is focus adjustment to compensate for thermal expansion.
All my shorter lenses focus at the infinity mark. I find the split
screen or matte is equally accurate, but on shorter lenses the split
screen is easier to see the focus. On a matte screen, the varimagni
finder is a help for critical focusing. On some lenses, the addition
of the 2X-A causes the focus to move away from the infinity mark. I
have also noticed that with zooms the infinity focus point will
change a small amount at different focal lenghts. I doubt you have
anything defective - just learn and remember what lenses focus at
what mark on the lens. On a few of my lenses, I have made small tick
marks on my focus scale for infinity focus with white ink so I can
set it quickly for shots I know should be set for infinity. Remember
if you are stopped down all this becomes much less critical.
--- Dean Tyler <dtyler@xxxxxxxxxxxxxx> wrote:
>
> Dear Oly Gurus,
>
> I recently noticed that my lens focus just past infinity on both of
> my OM
> bodies (OM2n,OM2s). I noticed that when the matte screen looks in
> focus I
> am just a little before my lenses stop at infinity. It is more
> pronounced
> on one body that has been used for years. The second body which
> focuses
> closer to infinity was CLAed by John in the Spring. If I look
> through the
> viewfinder at a distant object the split screen doesn't line up.
> If I back
> off the focus a tad, it does. The same goes for the matte.
>
> First question: Is this common?
>
> Second Question: Does this mean that focusing on closer objects
> with the
> split screen it will be a little off also or does the focus
> accuracy get
> worse the further objects are from the lens?
>
> Third question: Assuming the lens are focusing correctly (which
> have been
> checked a local shop) where could the problem be (mount, mirror,
> screen, or
> all three) and is there a way to figure it out.
>
> Fourth question: Should I just matte focus and forget about it?
>
> Dean
=====
Don Shedrick
http://groups.msn.com/firstlightimaging
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