Julian Davies wrote:
>The OlyAmerica reply makes no more sense to me now than it did in 2003.
>
First, I have assumed that the Oly letter was in response not to the
question asked, but to the question the answerer imagined to have been
asked and/or had an answer to at hand. Remember, the curtain change was
never announced. Oly had made a big deal of the curtain, with ads
showing it when the OM-2 came out. They could hardly make a big deal of
the change without admitting that there was something wrong with the
design. We really don't know who this guy was, how knowledgeable he was
or hwat agenda he had. I have a lot of experience with corpthink about
communications with customers and the public. Oly could easily have had
a policy of avoiding direct discussion of the change and the reasons for it.
>If the metering were full frame average at ALL speeds it would mean that
>there is no difference between the curtain and the film. Apply that to "for
>all versions" and there is no difference between the two curtain designs,
>since either is thus exactly the same as featureless film.
>
I believe the curtain change was in 1978 and the OM-2n replaced the
plain 2 in 79. Fernando wrote to Oly in 81. It is entirely possible that
the document sent to Fernando referred to OM-2 vs. OM-2n, rather than
early vs. late OM-2 or 2n vs. both versions of 2.
>So why did they change curtain design? Maybe they just fancied a bit of
>double inventory, or perhaps the research budget needed spending.
>
Now we get to forensic reasoning. There had to be a significant problem
that had surfaced with use of the cameras.
Unless we assume Oly is simply lying, we must assume that late 2 bodies
and all 2n bodies have full frame averaging, so any scenario must end up
there.
Possibility 1. Assuming crossed vertical centering from the SBCs and
horizontal centering from the curtain pattern was how it worked, I can
only see one problem. In exposures over about 1/30 second, the
horizontal component of the metering would become less and less with
slower speeds, leading to a vertically center weighted metering.
Vertically weighted metering can be a bad thing in some situations,
particularly in landscapes and especially in landscapes with a bright
sky and dark land below, exactly where longer exposures would often be
needed.
A possible clue is in the Oly pub. quote
"...The metering pattern of the two models are the same. Full frame
averaging at all shutter speeds on automatic and center-weighted on manual.
" perhaps the inclusion of the phrase "Full frame
averaging at all shutter speeds" indicates the metering pattern was
different at different shutter speeds before. If this were the case,
changing to an evenly weighted curtain pattern would just extend the
problem to all shutter speeds. It seems quite an unlikely scenario and
violates the assumption above.
Possibility 1a. Everything the same as 1 except that the response
pattern of the SBCs is changed to overall average when the curtain
pattern is changed.
Possibility 1b. The vertical centering of the SBC coverage is very mild,
wasn't changed, and Oly is fudging when they say is is overall average.
I'd like to think this isn't true. I also think think it would be well
known by now because of the problems people would have noticed.
Possibility 2. If the coverage of the curtain/film by the SBCs is
unweighted, then the original curtain design gives horizontally center
weighted metering. This is a sensible weighting for many photographic
situations, including most landscapes. However, it has the drawback of
giving different readings in horizontal vs. vertical framing. If they
initially thought the advantages outweighed the problem and went with
horizontal center weighting, then found through user feedback that it
wasn't working, changing the curtain pattern is the only solution that
doesn't require serious redesign of the whole system.
>John H has already confirmed no significant change in the cell board.
>
Possibilities 1a and 2 are the only ones I can think of that make any
sense. If there is no change in the circuit board, the only way for 1a
to work is if the actual SBC assemblies were changed through changing
the lenses and/or masking/unmasking or changing the size of the SBCs
under the lenses. I can't see any difference, but my early pattern OM-2
is not well at the moment. It only fires at a high speed, no matter what
is set, Auto, Manual, any speed, so I can't open it with B and look
through the back. Looking at the cells with a mirror, I can't see any
obvious difference from the OM-2n, but it is hard to tell that way.
Moose
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