Hi Ken, C.H. and all,
C.H. Ling wrote:
> No, the point is to have manual shutter control + TTL, say use 1/8s with
> > TTL.
<snip>
> >On the other hand, TTL flash in OM system only provide average metering,
> it
> > seldom provide accurate exposure as the object are usually too small or
> > background is too far away to provide enough/proper reflection.
I agree. Please excuse my ignorance, but I don't see the point of TTL flash
with slow-sync... at least from the point of view of the OM-2/OM-2n
behaviour.
Let's check if I understand it: when shooting with an OTF OM with a ready
flash connected, the first curtain (the one with the dotted pattern) starts
moving and uncovering the film beneath it. At the same time, the OTF sensors
start integrating ("accumulating") the light measured over the film (or
curtain) plane.
The curtain will take almost 1/60 sec. to fully uncover the film. If ambient
light was strong enough, the integrated value will reach the proper level
before that, and then the second curtain will start its travel in order to
cover the film and finish the exposure. Since the whole frame was never
uncovered, flash won't trigger -- it wasn't necessary.
But if the ambient light is low (typical need for flash) the integrated
value after the trip of the first curtain won't reach the desired level, so
with both curtains fully open, flash will trigger. Then things happens much
faster: the much brighter light from the flash will increase quickly the
integrated exposure value. If the proper value is reached then, the camera
sends a signal to the dedicated flash in order to quench the dump -- just
releasing the second curtaing would be way too slow for this. Since correct
exposure is achieved, 2nd curtain closes (with flash already off).
However, if after a full flash dump the proper exposure isn't achieved
(subject too far?), the difference between the plain OM-2 and the OM-2n
arises: the older model, since the integrated value is still below the
expected one, will continue the exposure with both curtains open -- now
integrating at a much slower rate, because the ambient light is so low. Only
after proper exposure is achieved, the second curtain will close, as always.
This "correct exposure guarantee", however, can be quite disturbing, becuase
the camera will do a long exposure (with probably blurred picture) when it
wasn't expected to do so -- that's what the flash was used for.
Since the newer OM-2n "knows" when a ready flash is connected, it handles
this case in a different way: after a flash dump, no matter if quenched or
not, shutter will close, effectively ending the exposure after 1/60 s. If
the flash power was not enough, LED won't blink in the viewfinder and you
get an underexposed picture -- you may try again with different settings.
It's possible to mimic the behaviour of the older OM-2 with a OM-2n -- just
insulating the "flash ready" contact. Not knowing there's a flash, the 2n
will behave as with ambient light exposure, keeping the shutter open until
proper value is achieved. The flash quench signal will be sent anyway.
I believe the opposite is also true, more or less: if you shoot with flash
with a plain OM-2 in the "OFF" position, you get all the benefits of OTF
exposure _but_ the shutter won't stay open longer than 1/30 or so, even in
case of underexposure.
So, my question is: if the TTL quench signal is sent when correct exposure
is achieved, what's the point of keeping the shutter open? If the OTF flash
metering was some kind of spot, it could make sense -- the centered/closer
subject is already well exposed, but the outside/farther background isn't.
However, as C.H. mentioned the metering is averaged, so if there's too much
background, the subject will be overexposed anyway :-(
AG wrote:
This is one reason I still love using the IS-3/G40 combo. The flash power is
> set by distance as determined by the autofocus.
Sure. It's like a manual, continuosly variable flash, without the hassle --
almost foolproof. The system works very well on compacts, like the mju-2 /
Epic.
BTW, I had a compact (Ric*h GR-1) whose flash behaved very strangely...
seems like it tried to balance the ambient light with the flash dump, with a
rather slow sync speed (1/30, a real shame with leaf shutter). It usually
rendered blurred backgrounds and, when shooting at totally dark locations,
ALWAYS underexposed the subject, no matter how close.
C.H. Ling wrote:
> > My most wanted feature on the OM System is high sync speed
That's great for fill-flash (which in the oldest leaflets for the OM-TTL
flash system was marked as 'possible' but not 'recommended') but, if you
just want to be able to use a large aperture (in order to reduce the DoF) a
ND filter and/or slow speed film and/or a powerful flash may suffice.
However, freezing the motion as in your fashion pic definitely needs high
sync speed.
I rarely use fill flash... however, I had to take recently some pics with
kind of "extreme tonal range" so I popped up the tiny flash on the, ahem,
EOS-300D and let it do all the magic. Fortunately it does 1/200 flash sync.
See a sample at <http://cjss.sytes.net/post/CarmEnrique/IMG_0560.jpg>
Cheers,
--
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
--
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