I've been trying to get this full synchro flash stuff (and OTF flash in
general) straight in my head (trying to convince myself to trade in an OM-4
for a -4Ti, I guess!). Someone correct me if I'm wrong here:
OTF Flash (OM-2n, OM-3Ti, OM-4, OM-4Ti):
1. First curtain begins to open, meter starts accumulating exposure off of the
film and curtain
2. First curtain fully open - Flash fires
3. Meter quenches flash and starts closing the second curtain when sufficient
exposure is measured (or flash fully discharges)
4. Second curtain closed - effective shutter speed 1/60
I think step 4 is different for the OM-2 (not the -2n) in that the shutter
will stay open as long as necessary to achieve sufficient exposure, even if
the flash power was insufficient.
Full Synchro Flash (OM-4Ti):
1. First curtain opens, flash begins discharging, meter starts accumulating
exposure off of the film and curtain
2. When sufficient exposure is achieved, meter triggers the second curtain to
begin closing, flash continues to fire
3. Flash stops when the second curtain is closed
I assume the OM-77 handled full synchro flash the same way
Full Synchro Flash (OM-3Ti)
1. First curtain opens, flash begins discharging
2. Second curtain begins closing to achieve shutter speed selected on ring
3 Flash stops when the second curtain is closed
Notice that since the OM-3Ti's meter can't control the shutter, the F280 is
acting essentially like a manual flash, therefore the need to do the GN
calculations. In fact I don't think the OM-3Ti's meter is used at all during
full synchro flash.
I don't think it's possible for the camera to control the intensity of the
flash based on an OTF reading, because it would have to adjust the intensity
*during* exposure, resulting in different exposure on different parts of the
frame as the shutter "slit" passes over the film.
Since the output from the flash is constant, the only way to control the
amount of fill flash is to vary the flash to subject distance (I think). I
recall it was said here once that changing the exposure compensation dial on
the OM-3Ti will provide varying fill rations. The way I see it, since the
camera has no control over the flash other than to start it when the first
curtain starts moving and stop it when the second curtain closes, changing the
exposure compensation dial will only vary the total exposure, not the
flash/ambient mix.
Do I have this right?
Paul Schings
Coventry, RI
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