Thank, Paul. What can I say? Bummer. I understand the concepts but don't
understand why this should be. So I can't use the flash in Auto mode with
the 4T?
-----Original Message-----
From: owner-olympus@xxxxxxxxxxxxxxx
[mailto:owner-olympus@xxxxxxxxxxxxxxx]On Behalf Of Paul Farrar
Sent: Thursday, August 01, 2002 11:33 AM
To: olympus@xxxxxxxxxxxxxxx
Subject: Re: [OM] Back Home to Flash Trouble
>
> Just got back from my trip to Atlanta (I missed you all), and went to a
> friends house for a party. Using my OM-4T, BG2, and T-32 flash I took a
> number of pictures inside using ASA 160 film. A number of times the
> viewfinder display showed "Under" (indicating underexposed), the flash
> indicator on the flash and in the viewfinder both seemed to indicate that
> the photo was exposed properly. I got the shots back and of course most
> were underexposed.
>
> I was using the T-32 on Auto, the camera on Auto, and didn't use an f-stop
> more that f5.6 for the shots (mostly using a 28-48mm zoom). Am I
suffering
> from a case of stupidity an missing something or is there a problem? I
also
> tried later without the BG2, and also tried using an F280 flash, all with
> the same result.
>
> Any help is appreciated.
I've seen this. It appears to be a quirk of the OM-4T (and
probably similar cameras like the 3 s), not a defect in your own
camera. I experienced it once in similar circumstances, indoor
pictures of a family gathering. Seeing something weird was going
on, I immediately switched to manual and used GN methods. When I
got the negatives back, the ones for which I got "UNDER", and a
flash OK, were severely underexposed. All had another thing in
common: there was a very bright lamp in the picture.
Apparently the sensing for flash and ambient light have different
properties. The "UNDER" and "OVER" lights are lit according to the
total flash+ambient during the whole exposure. The flash OK
signals that the flash was turned off before the capacitor charge
was completely exhausted. So if the flash is turned off too early,
the flash OK will pulse (because the capacitor was not fully
discharged), and the "UNDER" light will come on (due to percieved
underexposure). It's not clear to me why flash sensing and total
exposure sensing should have such different properties (in rare
cases like this), especially since they use the same sensing cell.
I think it's due to the different reflective properties of the
film and the shutter curtain. The flash takes place only while the
film is completely uncovered, but the combined flash+ambient
sensing, which controls the "UNDER" light, is a mix of curtain and
film metering. The more mirrorlike film surface may have been
reflecting the bright lamp into the cell, and shutting off the
flash early.
So I don't think there's anything wrong with your equipment. Mine
has worked flawlessly for several years since. Just recognize the
situation early and switch methods. A bigger problem I run into
nowadays is all the reflective fabrics that it's stylish to put on
everything under the sun. These confuse the heck out of flash
sensors, and cause severe glows from unexpected places like shoes,
coats, and bags.
Paul
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