Yes the 280 does a series of pulses and all the pulses may NOT be equal so
you may find uneven exposure across some frames.
_________________________________
John Hermanson www.zuiko.com
Camtech, Olympus Sales & Service since 1977
21 South Lane, Huntington NY 11743-4714
631-424-2121 For Free Olympus manuals,
please call 1-800-221-3000
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----- Original Message -----
From: "Tim Chakravorty" <suchismit@xxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Monday, September 09, 2002 4:31 AM
Subject: Re: [OM] F280 Super FP revisited
> >Therefore, for an "FP" flash to work, it must always have
> > the same, long burn duration, regardless of shutter speed.
>
>
> I think you are assuming that the flash remains ON for the entire time it
takes the slit to traverse the focal plane. That
> may not be true. I remember reading somewhere that in super sync mode the
flash output is not continuous but
> a series of pulses. How many pulses would that be.. If we divide the
length of the rectangular focal plane by the
> width of the slit - that gives us the number of slits that can be fitted
all at once on the plane. And since we want
> illumination in 'all of the slits' there will have to be so many flash
pulses. In other words, the flash fires every time
> the window moves a distance equal to its width.
>
>
> Now lets say the length of the focal plane is about 36mm. The max syn
speed with a regular flash is 1/60 sec.
> The window therefore moves at a constant speed of 36x60 ~ 216 cm/s . If
the shutter speed is any higher than
> 1/60s the slit only narrows but still moves with the same speed. IMO a
flash duration of 1/60 s is too long, they
> typically go from 1/500s and up, and is why its pulsed.
>
> -Tim
>
>
>
> ----- Original Message -----
> From: "John A. Lind" <jlind@xxxxxxxxxxxx>
> To: <olympus@xxxxxxxxxxxxxxx>
> Sent: Sunday, September 08, 2002 9:49 PM
> Subject: Re: [OM] F280 Super FP revisited
>
>
> > At 22:48 9/8/02, Pete wrote:
> >
> > >I'm confused again. If Super FP mode allows full synchronization at
all
> > >speeds, then the flash duration should be dependent upon the shutter
speed
> > >and not be a constant of "about 1/25 sec", no? I seem to remember a
post
> > >(by John L.?) explaining that Super FP mode operates as follows: flash
> > >starts, shutter opens, shutter closes, flash stops.
> >
> > Yes, that's the sequence.
> >
> > > If true, and I believe it is, then the flash duration will be the
> > > shutter speed plus the time before and after the shutter operates.
And,
> > > the longer the shutter opening, the less flash power that will be
> > > available, according to the charts.
> >
> > No. With focal plane shutters, total time it takes for a curtain to
travel
> > across the film gate remains constant, regardless of shutter speed. You
> > have two curtains, an opening one (leading) and a closing one
> > (trailing). What varies with shutter speed is the delay between
releasing
> > the opening one and releasing the closing one. In other words, it's the
> > *gap* between them that changes. Shutter speeds faster than the X-sync
> > speed have a gap that is narrower than the film gate. At those speeds,
the
> > closing curtain is released before the opening one has completely
traveled
> > and the result is a slit moving across the film gate. The faster the
> > shutter speed, the narrower the slit, but the slit itself *always* moves
at
> > the same speed. Therefore, for an "FP" flash to work, it must always
have
> > the same, long burn duration, regardless of shutter speed. And . . .
the
> > narrower the slit traveling across the film gate, the less light from
the
> > flash that's allowed to reach the film.
> >
> > >Because of the radically reduced flash power as shutter speed
> > >decreases, it seems that Super FP mode is *only* useful as a fill
> > >flash, and nothing more. No?
> >
> > Super FP imposes noticeable limitations on working distance compared to
> > using the same film speed at X-sync with TTL Auto. The faster the
shutter
> > speed, the greater the limitations.
> >
> > -- John
> >
> >
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> >
> >
>
>
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