There could also be a difference in exposure if using an ordinary polariser
instead of a circular one.
Different films also cause different auto vs manual exposures on the slower
speeds since they reflect differently. See
http://www.markcassino.com/essays/ttlflash.htm and
(from http://zuiko.sls.bc.ca/swright/archives/1999/msg17893.html )
Film ASA rating-for-OTF 0iff
Agfachrome RS 100 100 100 0%
Agfachrome RS 1000 1000 1000 0%
Agfachrome RS 200 200 200 0%
Agfachrome RS 50 50 64 28%
Fujichrome RDP 100 100 0%
Fujichrome RFP 50 64 28%
Kodak Ektachrome 100 100 100 0%
Kodak Ektachrome 100+ 100 100 0%
Kodak Ektachrome 200 200 200 0%
Kodak Ektachrome 64 64 64 0%
Kodak Ektachrome 400 400 320 -20%
Kodak Kodachrome 64 64 50 -22%
Agfacolor XRS 400 400 320 -20%
Agfacolor XRS 200 200 160 -20%
Agfacolor XRS 1000 1000 640 -36%
Agfacolor XRS 100 100 100 0%
Agfapan 100 100 80 -20%
Agfapan 25 25 16 -36%
Agfapan 400 400 250 -38%
Fuyicolor 160 NSP 160 125 -22%
Fuyicolor HR 100 100 100 0%
Fuyicolor HR 400 400 320 -20%
Ilford FP-4 125 80 -36%
Ilford HP-5 400 250 -38%
Ilford Pan-F 50 32 -36%
Ilford XP-1 400 250 -38%
Kodak Ektacolor Gold 160 125 -22%
Kodak Kodacolor Gold 200 160 -20%
Kodak Plus-X Pan 125 100 -20%
Kodak TMAX 100 100 64 -36%
Kodak TMAX 400 400 250 -38%
Kodak Technical Pan 25 16 -36%
Kodak Tri-X Pan 400 250 -38%
Kodak Tri-X Prof. 320 200 -38%
Kodak Vericolor Prof. 400 320 -20%
Kodak Vericolor III 160 100 -38%
Kodak Vericolor HC 100 80 -20%
Tom
On Wednesday, June 12, 2002 at 11:22, Winsor Crosby
<olympus@xxxxxxxxxxxxxxx>
wrote re "Re: [OM] OM 4 (Auto) - Shutter speeds" saying:
> Angel,
> >
> > If the row of bars is halfway between 1/125s and 1/250s, can the camera
> >work
> >on 1/180s or 1/215s, for instance ?
>
>
> Yes. There have been previous discussions of this on the list. You
> are right. I could not find where Olympus mentioned it in the small
> collection of printed stuff I have.
> >
> > When I have buy my first OM 4 (1987) I have check this matter and the
> >slides
> >are always sub or over exposed. I work always on Manual mode, so on that
> >time I have forget this matter. Some days ago I have tested my OM 4 camera
> >one more time shooting on Auto mode with the bars halfway between 125 and
> >250 and shooting the same picture on Manual mode with ex. exposure. The
> >slide on Manual mode has perfect exposure and the slide on Auto mode is 1/2
> >stop sub exposed.
>
> There is probably something else going on. The manual setting is
> based on the electronic calculation of the light transmitted through
> the first mirror and reflected by the second mirror onto the meter
> cell on the floor of the mirror compartment. The automatic
> calculation is based mostly on the reflection of light from the
> pattern printed on the1st shutter curtain and from the film base onto
> the same meter cell depending on the shutter speed. Olympus in the
> owner's handbook says the automatic "off the film" metering system
> works expecially well_if the frame is evenly illuminated_.
>
> I suspect the difference is not due to any malfunction but in the
> difference between your careful manual metering that is tailored to
> your subject, and the inflexibility of the automatic system,
> especially since you say that the exposure difference may go in
> either direction. If it was consistently over or under exposed in
> automatic and more than a 1/2 stop, then there might be a malfunction
> that needs repair.
>
> My thoughts, but no expert.
>
> Winsor
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