It's interesting to find out in the last few posts of this thread that
the automatic exposure metering system of the OM-2 originally used a
pattern different from the usually documented full frame averaging
system (e.g. Shipman, 1981, p58 -- it seems I have the same edition as
Walt!).
But that doesn't actually answer the question originally put by James,
one that I've also been puzzling over for a while and still have
only half an answer, which is basically about how to use centre-weighted
metering as it is in the 2n to help with zone metering:
> At 4:10 PM +0000 2004.02.11, James Royall wrote:
> <SNIP>
> ... Someone here suggested looking over
> www.kenrockwell.com, where I found his version of the zone system. This
> and presumably any other more 'controlled' exposure technique requires
> metering a zone in the scene.
and in particular
> Is this completely impossible with the
> centre weighted meter in the OM2n? What if there is a substantial area
> that can be metered? How big a proportion of what is in the viewfinder
> would it need to be to give an accurate reading? Failing this is it
> possible to meter off a grey card and adjust?
So the real question is about the sensitivity characteristics of the
"centre" of the centre-weighted CdS viewfinder metering system, and what
guidance that can give in making exposures.
*** Basically, is that centre area in any way useful as a "spot" for zone
metering ????
Shipman repeatedly describes the system as centre-weighted, and on p52
defines c/w via a diagram of a circle (in the middle of the frame) of max
sensitivity, and writes "meter sensitivity gradually decreases towards the
edge of the frame." He also writes (p56) that "the sensor measures
brightness of the focusing screen using a center-weighted pattern".
So, it seems that the focussing screen determines the nature of the centre
weighting.
*** Is anyone able to quantify how ????
I have tried by moving the viewfinder around an area with a bright light
source in it, and watching rate of meter movement, but that's not been very
successful because the light isn't close enough to being a point.
Nonetheless, what I see suggests that the centre is quite
diffuse i.e. it occupies quite a bit of the screen and with a slow
roll-off towards the edge.
Would be interested in further comments.
thanks
Andrew
(James, please correct me if I'm off beam in interpreting your question!)
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