Moose,
I think you nailed it. But, just to clarify, you seem
to be mixing up the term "TTL" (Through The Lens)
metering with "OTF" (Off The Film) metering. Of
course, as with most SLRs, ALL metering on the OM-4 is
"TTL", Including spot metering. But as you point out,
in auto mode the "OTF" meter deterimines when to close
the shutter during the exposure and may sometimes be
different than the pre-exposure reading (especially if
there is no film in the camera).
-Steve
--- Moose <olymoose@xxxxxxxxxxxxxxx> wrote:
>> You are dealing with 2 completely different
exposure
> systems here. In
> Auto Mode, the camera reads the light falling on the
> first curtain and
> the film until enough light has accumulated to
> complete the exposure
> (slightly simplified). In Spot Mode, there is no way
> to do TTL, even
> with only one spot, because the camera has no way to
> know if the spot
> metered is still in the same place in the frame. In
> Multi-Spot, it is
> even clearer that exposure cannot be done TTL. So in
> Spot, the exposure
> set in the viewfinder is set and used as a fixed
> speed when the shutter
> is released.
>
> So what is happening is that the two systems
> disagree about the correct
> exposure.
>
> >Am I doing something wrong?
> >
> Very likely, and if so, that's the good news. If you
> don't have film in
> the camera while you are playing around, you will
> get this effect. The
> TTL meter is calibrated to read based on the average
> reflectance of film
> and the pattern on the first curtain; at the speeds
> you are testing,
> mostly the film. When you use the camera witout
> film, the system reads
> the reflected light off the all black pressure
> plate, thus giving longer
> exposures. To play around with any of the OM bodies
> with TTL exposure,
> you must put a roll of junk film in to get correct
> results. The cameras
> all came new with a little piece of gray cardboard
> in the film plane,
> but they are long gone for most bodies.
>
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