Thanks Winsor for your kind reply.
I did not exchange the focussing screen. The OM4 has the 2-4, the
OM4Ti the 2-13. I was just speculating if that might be the eason
that they behave differently.
Yes, I used a wall as well. Same thing. With the wider lenses the OM4
showed one Stop difference between center-weighted and Spot reading.
Any more suggestions? Maybe a CLA is advisable?
Cheers, Thomas
Date: Thu, 16 Jan 2003 12:39:50 -0800
From: Winsor Crosby <wincros@xxxxxxxxxxxxx>
Subject: Re: [OM] advice needed: SPOT meter reading differs from
AUTO on gray card??
Hello Ladies and Gentlemen,
a Happy not so New anymore Year to all of you.
By chance I noticed something with my OM4 (focussing screen 2-4)
which puzzles me: I took a reading from gray card in AUTO (center
weighted average), then pressed the SPOT button, and the little
diamond jumped one full Stop to the right (double exposure time).
The compensation dial was set to Null.
I did some more testing: This happens mainly/only with the 21f3.5 and
24f2.8, but not with the 28f2 or 50f1.8 (this selection is based on
lens availabilty). I also tried my OM4Ti/2-13 focussing screen with
these lenses and with all of them there was no difference between
center-weighted and spot reading. And with both cameras and with all
the lenses the center-weighted AUTO reading was identical and precise.
Does anyone have an idea what is going on? Does the combination of
2-4 focussing screen and very wide lenses cause this difference? Is
there something wrong with my camera?
I would appreciate your input!!!
Thanks and best wishes,
Thomas
--
The focusing screen does not have anything to do with the metering in
the OM4. The light being measured is passing directly through the
mirror and being reflected down by the secondary mirror toward the
sensor in the bottom of the mirror box.
If you found variations that disappeared by changing screens your
methods are suspect. I think that if you carefully recheck the
variation will have disappeared. Uniform illumination of the field
is necessary to make this kind of comparison which is hard to do with
a gray card. It would have to be very large to fill the field of a
21 mm lens and still be in focus. I would suggest that you use a
uniformly lit wall.
- --
Winsor Crosby
Long Beach, California
------------------------------
--
Dr. Thomas Müller
Max-Delbrück-Center for Molecular Medicine
AG Medical Genetics
Robert-Rössle-Str. 10
13125 Berlin
Germany
phone: 49 30 9406 2842
fax: 49 30 9406 3449
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