Thanks for the info straight from the 'horse's mouth'. There just have
been a change in the coverage/sensitivity of the photocell(s) when they
changed the curtain pattern to maintain the same averaging reading. The
curtain patterns are quite different as you can see here
<http://brashear.phys.appstate.edu/lhawkins/photo/om2-curtains.shtml>.
The old pattern was certainly not center weighted in the radially
symetric way one would expect, being equally bright all the way to the
edges horizontally, so it probably compensated for a nonlinear
sensitivity in the sensor module. Since the change was likely made to
solve a problem with exposure at speeds where part of the exposure was
off the non random curtain pattern and partly off the evenly reflective
film, they clearly didn't have a way to make OTF center-weighted at the
time. According to Shipman, they solved that problem in 2S, 3, 4 series
and OMPC bodies by creating the center weighting in the configuration of
the secondary mirror.
Moose
Fernando Gonzalez Gentile wrote:
on 9/06/2003 11:09, Pschings@xxxxxxx at Pschings@xxxxxxx wrote:
In a message dated 6/9/2003 8:45:30 AM Eastern Standard Time,
fgnzalez@xxxxxxxxxxxxxxx writes:
It is useful to know that in Manual mode the OM2(n) reads
center weighted, but in Auto reads average.
I'm not so sure this is true. I distinctly remember reading somewhere
(Shipman, maybe? - I'll have to check my copy when I get home)
My Shipman is a later one that doesn't cover the OM-2(n), so it doesn't
address the issue. The OM-2 instruction manual doesn't focus on the
issue, but the specifications state that it is center meighted in Manual
Mode and do not do so in the section on Auto Mode. Since it is really a
non-useful inconsistency that could cause unexpected exposure results in
certain situations, I suppose it is natural that they wouldn't directly
lie about it, but wouldn't call attention to it either.
So as not to suffer from nightmares any more, I asked Olympus America and
their reply, on my left knee righ now -beautiful almost translucent paper- ,
says:
"Dear Dr. Gonzalez-Gentile:
This is in reply to your recent inquiry concerning OM-2 and OM-2N metering
patterns.
The curtain design was changed in 1978 to the present form, as outlined in
the Xerox copy from an Olympus publication. Unfortunately, extra copies are
not available, therefore, this copy.*
Your continued interest in Olumpus products is deeply appreciated. Should
further information be requires, please do not hesitate to contact me.
Sincerely,
[authentic blue Parker ink hand signature]
Ralph Lepore
Service Representative
April 3, 1981"
And the Xerox copy:
"...The metering pattern of the two models are the same. Full frame
averaging at all shutter speeds on automatic and center-weighted on manual.
The viewfinder display is center-weighted at all times, even when the
camerea is set for automatic operation."
Add this to the reasons for differences in shutter speed between
viewfinder display and actual auto exposure in my reply to ajai krishnan.
From my experience with my 532784, it does average on Auto. I fooled too
much to forget.
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