--- Charles Cabaniss <[EMAIL PROTECTED]> wrote:
> Bob, et al,
>
> How easy is it to knock the mirror out of alignment
> (on any of the EOS
> bodies)? Certainly I would not apply firm pressure
> such as pressing your
> finger behind lens paper (or the like) and rub. But
> how 'bout using a soft
> Q-tip moistened with isopropyl alcohol, applying
> only the slightest
> pressure... would that be enough to cause
> misalignment?
I honestly can't say, as I've never done this. I
would certainly try to be VERY gentle.
>
> Also, forgive my ignorance but I'm new to EOS and AF
> systems, how exactly
> does a misaligned mirror throw off auto-focus? I
> imagine that a misaligned
> mirror renders the image in-focus thru the
> viewfinder (with manual
> adjustment) but out of focus on the film.
I never said it would be out of focus in the
viewfinder, although that's possible, too.
On the back of the main mirror is a small secondary
mirror that reflects a portion of the image down to
the AF sensor(s) in the bottom of the camera. If the
angle of the mirror shifts, the part of the image
reflected to the sensors may not line up with the
marks in the viewfinder. Wouldn't be good if you
thought you were focusing on the eye and were really
focusing on the ear!
As for the viewfinder and manual focus, the same basic
thing occurs. If the mirror position is off, the
length of the light path to the focus screen can
change. But the length of the light path to the film
is unchanged, of course.
=====
Bob Meyer
I wish I knew what I know now, when I was younger...
http://www.meyerweb.net/epson
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