At 11:06 PM 9/22/99 -0400, Tom wrote:
>Too bad the f280 can't scan the scene in time with the shutter. Then
>we'd get a much better Guide Number.
If you mean adjust the output to a higher level but shorter duration
for higher shutter speeds, remember, the flash output has to remain on
for the length of the curtain travel. With 11-13 miliseconds for
curtain travel plus a bit more for the initial metering and response
time, the minimum time the flash *has* to remain on is about 1/60
second, even though the shutter speed maybe faster than 1/60. (With the
OM-707 it can be shorter due to faster curtains.) Hence, the GN will be
lower at higher speeds because the film sees less light, but the flash
has to remain on to cover the full curtain travel.
If, on the other hand, the flash full output potentially lasts 40ms (a
1/25 shutter speed) then it might be possible to get twice as much
output at 1/60 and above. Anybody know how long it takes an OM-4t to
meter and release the shutter? I assume the extra two contacts on the
top of am OM-4T are to trigger the flash before the 1st curtain in
super FP mode while the other contact indicates super FP mode to the
camera. Normal TTL flash fires after the 1st curtain has fully opened
and before the 2nd curtain is released, hence needs a different sync
time.
Wayne
Hopkinton, MA
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