>>
If the F280 is on Manual, isn't it just like any other flash with a GN of
28?
That is, it shouldn't vary with shutter speed.
<<
In manual mode you're right - it has a fixed GN of 28. I was thinking of
Super FP flash, normally used for shutter speeds faster as 1/60, but it can
also be used at longer shutter speeds (the 4tI needs to be set at manual),
in which case you can use flash light to emphasize movements, and allow
available light to be part of the exposure. The only problem with FP mode
and long shutter speeds, and this is true for both the 4Ti and 3Ti, is that
there's no automation and you have to use the GN formula.
The GN in FP mode varies with both shutter speed and film speed (see the
graph at the eSIF- http://www.e-sif.net/om-sif/flashphotogroup/f280.htm ),
but I have to make one correction to my previous mail: the GN stays at a
fixed 14.7 at 1/60 or slower (see the Super FP Flash Guide Numbers (m.)
table at the eSIF)
And of course there's a big difference in how the F280 operates at shorter
shutter speeds on the 4Ti vs. the 3Ti. The latter doesn't use its TTL
capabilities (you still must use the GN formula), the 4Ti does - it measures
the combined available light and F80 output and adjusts shutter speed when
necessary.
hnz
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