The F280 has a GN less than the T-32 and it plummets in Super FP mode. The
faster the shutter speed, the more it plummets . . . dramatically. This
greatly reduces the working distance of the flash.
Not unique to the F280, the plummeting GN issue dates to the days of long
duration FP flash bulbs (e.g., 26 and 26B, the long duration version of the
Press 25). When you set the shutter speed above the X-Sync, you get a slit
moving across the film plane. The shutter curtains *always* travel at the
same speed, regardless of shutter speed. Thus, shutter speed is controlled
by the delay between releasing the first and second shutter curtains, not
their speed of travel. As shutter speed increases, the delay decreases and
the slit narrows. Each time the shutter speed doubles (e.g. from 1/125th
to 1/250th) the width of the slit is cut in half, and this cuts in half the
light reaching the film from a flash in FP mode, or long duration flash
bulb for that matter.
Look at the table for the flash on the eSIF site. With the OM-3ti or OM-4T
in FP mode, the flash GN drops from 28m/92ft (ISO 100, meters/feet) to:
ISO 100
Shutter GN(m) GN(ft)
1/60th 14.7 48.2
1/125th 10.4 34.1
1/250th 7.3 23.9
1/500th 5.2 17.1
1/1000th 3.7 12.1
1/2000th 2.6 8.5
Even at f/4 to maintain a decent depth of field with human subjects, at
1/125th second shutter speed in Super FP mode, the maximum working distance
is very short:
GN for 1/125th @ f/4
ISO 100: 2.6m / 8.5 ft
ISO 200: 3.7m / 12 ft
ISO 400: 5.2m / 17 ft
Consider the severe maximum working distance limitation amd compare it to
the working distance and film speed you normally use with fill flash before
buying the F280.
-- John
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