> 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
>
John,
My calculations for fill flash are as follows, and are presented for
corrections or scrutiny; all comments welcomed.
I like to start with my most likely situations. If the fill flash is for
portraits outdoors on a sunny day, then I may as well start with what are
the "invariables", that is, I will want to use a suitable film, most likely
Kodak Porta 160. Also, it is likely going to be sunny, or at least slightly
overcast. And I will want to use a 50mm lens, and as well will probably want
to use a lens around 80 to 100mm for proper perspective on the faces.
If I use any of the OM's with 1/60 sync, even at f16, the film is
overexposed about 2 stops, which is about what Kodak Portra will tolerate,
and the shutter speed is a bit slow for hand held shots with the longer lens
length. Also, f16 is a difficult aperture to work with with a flash.
By going to the OM2000 with 1/125 sync speed, the shutter speed becomes more
workable for the longer length of lens, and I can open the lens up to f11,
or maybe even f8 if it slightly less than full sun. The f4 example that you
give above is not something that I could often use in real life.
Okay, if I use a T32 in manual mode, my GN becomes about 40 with the Portra
160. If GN/aperture = distance, then 40/11 = 3.6 meters, or about 10 feet.
Since I'm happy with a bit less than full flash, then I could back off to
about 12 feet. At f8, which might be a little washed background for full
sun, but okay if slightly overcast, the distance increases to about 5
meters, or about 15 feet, maybe pushed to 17 or 18 feet.
If I combined a T32 and T20 with a flash bracket, in manual mode, then the
GN becomes about 48 with Portra 160, so the distance at f11 could be 4.3
meters, or about 13 feet, maybe up to 15 feet. At f/8 I could back of to 18
or 20 feet.
To me this is more workable in an actual situation, and is one reason for
owning an OM2000. I can't really afford the OM4t/280 combo anyways, but your
figures make it look less desirable even if I could.
Now if I could just trust the Cosina made camera to actually work :-)
Wayne
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|