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Re: [OM] OM TTL flash behaviour

Subject: Re: [OM] OM TTL flash behaviour
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 19 May 2011 12:21:02 -0500
Martin,

I'll attempt to nutshell this as I'm at a 5mph trot on a 6mph treadmill today.

The PenF, with the ability to sync at any supported speed would be my
first choice for this class. Besides, it will cut your film costs in
half. Manual everything is your first line of defense for learning the
ins and outs of flash.

The OM-3Ti is probably the only OM body that allows independent
exposure-compensation control of the flash. This inability to do flash
exposure compensation has been the weak point of the OM series. If you
adjust the exposure compensation, it will affect the background. If
you aren't trying to balance flash with ambient, then it's a
no-brainer--just crank that dial around to wherever you want.

As to the Vivitar 285HV, I'm a big fan of them and have three of them.
The photoeye in them is pretty good, but almost always underexposes.
Back in the ancient days of film, photographers regularily under-rated
their pro print films not because the engineers at Kodak were idiots
and didn't have a clue what an ISO meant, but because the flashes in
automode generally screwed up by half a stop. Underrating the film was
a way to compensate for that. However, my T45's photoeye is deathly
accurate.

It never stopped us from blaming the Kodak engineers though.

Back to the exposure-compensation on the OM-2n and how to use it to
balance flash with ambient:

You mention my recommendation of allowing the shutter speed to
indicate 1/30. This will place the ambient exactly one stop down from
flash. If you have it at 1/15 then the background will go two stops
down. This, however, isn't always the case because in most room you'll
have enough spillage from your flash to raise the background up a bit.
Of course, if you are outdoors at night at Niagara falls then there is
no way your flash will illuminate the falls. I'm more of a fan of two
stops down (1/15 indicated) because of not only my flash filling some
of the background, but it prevents blurring and keeps your
white-balance in check.

So for this discussion, let's use 1/15 as our baseline ambient exposure.

When you eyeball the scene and have a pretty good idea that your flash
will blow out the subject requiring a -1.0 EV compensation, I would
raise the background from my nominal 1/15 to 1/30 and then dial in the
compensation. This will keep the background the same exposure as 1/15
at 0.0 EV compensation.

When you eyeball the scene and have a pretty good idea that your flash
will underexpose the subject requiring a +1.0 EV compensation, I would
lower the background from my nominal 1/15 to 1/60 and then dial in the
compensation. This will keep the background the same exposure as 1/15
at 0.0 EV compensation. There is a gotcha with this, though. Depending
on the OM model, the flash may not fire if the ambient exposure is at
or greater than 1/60 because the camera already thinks there is enough
light and the flash is not required. We run into this problem with
outdoor fill-flash. Unless you have the OM-3Ti or the original OM-2md,
the flash will not fire.


> As a third question, AG and Dr Flash have talked about underexposing the
> background by 1 or 2 stops. One method mentioned was to set the aperture
> for 1/30 exposure, and letting the OM fire at 1/60.  I understand the
> concept - and here my ignorance is showing - but does this work in
> straight auto or in TTL as well?

Remarkably, I've gotten this method to work almost equally as well
with TTL and with the flash's photoeye. The important thing is that
the camera force-limits to 1/60. With my digital cameras, the E-1 and
A1 free-float the shutter-speed when a non-dedicated flash is
attached, but the L1 will force-limit up to the highest sync-speed
when it detects anything in the hot-shoe.

AG Para(normal)med Flash
-- 
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