What you report can be considered a classic case study
with regards to flash sync operation !
Normal sequence of events in Auto mode:
1. Camera automatically sets shutter speed to 1/60s.
(This is the max speed possible (OM)where the shutter
curtains would be fully open when the flash fires)
When the shutter is tripped, right curtain moves
from the left end to the right end,shutter is wide
open,
flash fires, after adequate exposure camera turns
the flash off and the left curtain starts to move to
the right, bringing the show to an end. Total
exposure duration at
any point on the frame = 1/60s, regardless of flash
duration.
What happened in your case :
At any speeds higher than 1/60s (OM), the left shutter
curtain will start to close (ie move to the right)
*before* the right shutter curtain has completely opened,
(ie before it has reached the right end of the frame).
How soon that happens depends on the shutter speed. At
1/125th it will be like a slit moving to the right, with
a width roughly equal to half the frame width. In other
words when the right curtain has completely opened the
left curtain has already half closed. At 1/250th, the
slit width would be about 1/4 that of the frame.
I believe the flash fires when the right curtain has
completely opened,regardless of the left curtain's
position. So in your case the left curtain must have
been 3/4 closed already leaving only the right 1/4 of
the frame to see the flash go off. Of course it fired
at full power, and as a result of the flash/subject
distance and aperture setting, the frame got overexposed.
Can you be more specific as to what fraction of the
right side of the frame got overexposed ?
-Tim
> Halfway through shooting a roll of film with flash, I noticed that I'd set
> it to 'manual', and thus all the shots I'd taken were at 1/250th, that being
> the default setting I use.
>
> Unsurprisingly, all I have on that half of the roll of shots is the
> right-hand side of the image exposed, and the left 3/4 is completely blank.
>
> What's weird is that the right-hand side is blown out all to heck -- the
> T32 was obviously firing at full power all the time, and when shooting, I
> certainly noticed it was firing, which was why I didn't think anything was
> amiss.
>
> A couple of questions:
>
> 1. Is this documented behaviour? I had the T32 set to the "TTL auto
> control" side of the panel, and looking in the PDF file from e-sif, I can't
> see any explanation of what it'll do if the flash is set to expect control
> from the camera, but the camera doesn't control it. Presumably the camera
> never says 'okay, that's enough light', so the flash keeps firing, I guess.
>
> 2. Is this _sensible_ behavior? If it were me, I'd rather have the flash
> not fire at all in this situation, because that would be a warning that
> something was wrong -- as it was, I happily shot off a dozen shots thinking
> everything was okay. I'm not quite sure how it would work electrically, I'll
> admit; perhaps have the 'stop firing' pin on the flash shoe start high if
> it's in TTL control mode and get pulled low, that way the flash would know
> that the camera isn't going to tell it to stop so presumably the camera's
> confused..
>
> -- dan
>
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