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Re: [OM] Mirror and Aperture Prefire

Subject: Re: [OM] Mirror and Aperture Prefire
From: "George M. Anderson" <george@xxxxxxxxxxxxxxxxxx>
Date: Sat, 10 Jul 1999 09:49:14 -0700
Thomas;

Glad you found this page, it should help in your search.


Thomas Haegin wrote:
> 
> Looked up at Gary Reese test page: What does that mean, how do you do a
> mirror and aperture prefire???

The, let's call em 'electronic', OMs; ie 2Sp, 4, 4T (and maybe others) 
have a self-timer which moves the mirror up and stops down the aperture
when you **start** the self timer.  This is the prefire he's talking
about. Simply use the self-timer on a tripod.  This is opposed to the
self-timer action on the original 1's (and 2's I think) which flip up
the mirror and stop down the lens **at the time the shutter fires**
causing undamped vibration in the camera system and thus usually poorer
results.  In fact, Gary R also found that even when he used mirror
lockup on an OM-1, the aperture stop down at shutter time was enuf to
reduce image quality.

As for lenses, the 200/4 gives fine results as long as you use and
support it properly.  And, BTW, I think this is all moot if you're
hand-holding.  When the telephoto lens/camera is properly held, your
body will damp out the vibrations.

Another lens to consider is the 65-200/4  I think there's also a Hoya
zoom in that range that's also been rated highly by listmembers,
including Gary S.


George



> 
> << Zuiko lenses in this weight and length class need additional support, as
> well as mirror and aperture prefiring, to attain their best results. >>
> 
> Copied from Gary Reese tests:
> 
> <<
> 200mm f/4 Zuiko (multi-coated)
> Vignetting = A
> Distortion = None
> 
> OM-4 with mirror and auto diaphram prefire, lens supported by a Bogen
> Telephoto Lens Support
> Aperture  Center    Corner
> f/4       B         B-
> f/5.6     A-        B+
> f/8       A-        B+
> f/11      A         A-
> f/16      A         A-
> f/22      B+        B+
> f/32      B         B-
> 
> Notes: Apparently superior results versus using an OM-1 (see below). Zuiko
> lenses in this weight and length class need additional support, as well as
> mirror and aperture prefiring, to attain their best results.
> >>
>

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