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Re: [OM] OM-40 (OM PC) and the 1000mm lens?

Subject: Re: [OM] OM-40 (OM PC) and the 1000mm lens?
From: Richard Schaetzl <Richard.Schaetzl@xxxxxxxxxxxxxxxxxxxx>
Date: Thu, 01 Apr 1999 12:39:05 +0200
Olaf Greve schrieb:

> Just a quick question out of sheer interest:
> I read in the OM 40 manual that came with my camera that the OM 40 can't be
> used with the Zuiko 1000mm lens. Is this true? If so, why?

That´s only true for Program mode, same with the 250mm/2.0 350mm/2.8 and
other super teles. I guess that´s because of the way the diaphragma is
set to a certain aperture.
The lever used by the Program mode was designed to close the aperture
from full open to the value defined by the aperture ring. Different from
Auto and Manual mode, Program mode requires to set the aperture ring to
the smalles aperture, the camera then don´t simply moves the aperture
lever to his extremes, but moves the lever in discrete steps to close
the diaphragma to the aperture chosen by the Program mode. With longer
lenses the aperture mechanics are not precise enough to guarantee the
desired aperture. Of course this doesn´t affect correct exposure because
the shutter speed will be determined after the aperture is closed, only
the indicated shutter speed in the finder might differ from the actual
used one.
BTW, IMHO: Program mode and super tele lenses are an nonsens combination
anyway.

Auto mode is not affected, because the aperture lever is used the way it
was designed. So OM Program mode is just a clever way to have Program
mode with lenses not designed for such an exposure mode.

Regards

Richard


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