Moose did indeed "nail it". I ran a test roll this morning before
work and the relationship of shutter to meter readings for
centerweighted Auto mode seemed consistent.
And I read the 'TTL' vs. 'OTF' as an early morning typo of the sort I
often make myself. ;o)
Cheers!/ScottGee1
On Apr 7, 2005 9:46 AM, Stephen Walker <stephenpwalker@xxxxxxxxx> wrote:
> 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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