Perhaps a short technical explanation would help here. Under the top cover
around the meter movement, there are 2 mechanisms, one electrical, one
mechanical. The electrical portion is a circular ceramic circuit with asa
resistors printed on the under side. Brushes rub on this circuit, top & bottom
controlling the actual auto exposure shutter speed.
The reading taken through the cds cells (which controls meter NEEDLE position)
does not go through this ceramic circuit. Auto shutter speed is controlled
completely independent of the needle indication. You could take the meter
movement out of the 2 & 2N and auto shutter speeds would still perform
perfectly, you just wouldn't know WHAT speed.
The mechanical portion of the meter mechanism is a cam that changes the needle
position by 1/3 stop each time you use one click of compensation.
The asa ceramic does get dirty and can affect auto exposure, but it will not
affect needle behaviour by turning the compensation dial (though this can clean
it temporarily).
John
Ken Norton wrote:
> The other Ken wrote:
> >This is an interesting thread. I just got my Sensia and Kodachromes back
> from
> >my trip to Greece and I am disappointed with the results of my OM2n. Too
> many
> >pictures appear very underexposed (dark, muddy). Most of my exposures were
> set
> >on Auto. (pictures from a bus and fast moving items are hard to get in
> Manual
> >mode). Sooo, I am getting an OM4T for its spot metering.
> >It seems that the OM2N either in need of calibration, the full screen auto
> >exposure is confusing me, or I need to set the exposure compensation at an
> ASA
> >other than the films recommended ASA.
>
> This is rather interesting. First of all, I'd say that since the pictures
> were leaning towards the underexposed side, it isn't the metering method,
> but the calibration. The "slightly center-weighted" metering of OTF is more
> than adequate for the 90% rule. I don't use spot metering very much and I'm
> more than happy with the OTF metering that my OM-2S and (recently sold)
> OM-2(md)
>
> What you are describing, I think, is a classic example of ASA Dial Dirt
> (ADD). Look through your viewfinder and wiggle the ASA dial. If the meter
> jumps around a bit, this is the problem. The short term solution is to
> rotate the dial back and forth a few times to "carve" an electrical path
> through the tarnish. Longer term solution is to have the camera maintained
> by a service center.
>
> Oh, great. Now that all of our children are diagnosed with ADD, we have to
> diagnose our cameras with it too.
>
> Ken N.
>
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