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[OM] Re:: DOF button.

Subject: [OM] Re:: DOF button.
From: "Brian Swale" <bj@xxxxxxxxxxxxxxx>
Date: Wed, 26 Dec 2001 21:06:01 +1300
Hi Roger and other fellow Zuiks.
> 
> Date: Tue, 25 Dec 2001 12:43:02 -0500
> From: "roger skully" <robinsnes@xxxxxxxx>
> Subject: Re: [OM] (Fwd) DOF button.
> 
> Why disable it or hinder your focusing abilities? I cannot think of any
> reason (not that there may not be one) for doing this.
> Roger Skully
> robinsnestphotography.com

Well, the logic behind it goes like this, as I understand it.

The 35mm system has a small negative. So for best results a bit more care 
is needed to eliminate anything that might contribute to unsharpness.

There are at least three 'in camera' sources of vibration that actually do 
result 
i lowered contrast and definition (see Gary Reese's lens tests - he 
comments on this frequently).  They are:-

Mirror operation
Diaphragm operation
Focal-plane shutter operation.

Mirror vibration is dealt with by raising the mirror (OM1) and pre-fire in self-
timer operation (OM4), and the delay that allows the vibration to die away.

Diaphragm vibration is dealt with in the OM4 by pre-fire, and not at all in any 
other OM body. Hence the wish to close down the OM1 diaphragm once the 
picture is composed and when the mirror is up. Then all that is necessary is 
for the subject to quit moving.

Shutter vibration is dealt with by attaching as much mass as possible to the 
camera. Clamp it to a mountain if possible. Otherwise, use a heavy tripod, 
something heavy at the tripod head or attached to the camera,  push down 
on it to anchor it to mother earth, and maybe hand-hold it as well to dampen 
the residual vibrations.

And as I said previously, the OM1 has it all over the OM4 in this regard since 
it is possible to get everything all set, and as soon as the wind stops - or 
whatever - trip the shutter. There is no way to do the equivalent with an OM4. 
With the OM4 you have to let the self-timer do its thing which takes 10+ 
seconds. OK for a subject that doesn't move, such as a mountain, but for 
flowers, insects etc  in macro mode etc - no way.

Does that cover it?

I agree that for wedding photography, things may be a little different. But the 
principles remain the same, in my view. And you will be very concerned with 
fine details of lighting, group composition, interactions and facial 
expressions 
that don't really come into it to the same degree with flowers. Well, lighting 
and composition do. But you have to use your imagination to see a smile.

Cheers, Brian
...................................................
Zuikoholics, enablers, one and all.
Feeding fantasies, emptying pockets!
---------------------------------------------------
      Brian Swale, 140 Panorama Road,
      Christchurch 8008, N.Z.
      Tel +64 3 326 7447
      http://homepages.caverock.net.nz/~bj/photography/

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