On Tuesday, April 23, 2002 at 16:27, frieder.faig@xxxxxxxxxxxxxxxxxxxxxxxxx
<olympus@xxxxxxxxxxxxxxx>
wrote re "Re: [OM] even more about the F280" saying:
> > 3.The GN must be higher for the OM77 because the sync speed is
> > higher and more of the frame is illuminated at any shutter speed. But
> > why is it higher at 1/100 (15.6) than for the 4T at 1/60 (14.7)?
>
> Is it possible that the flash recognizes the OM77, and then increases
> the frequency of flash emissions? -> different illumination times?
But why? Howcome the cheapo camera gets a little more than the professional
camera?
> Or is the frequency of flash illumination a fixed value for all FP-operation?
> Someone here mentioned, a while ago, it would be about 20kHz?
10Khz to start, growing to 17-20Khz after about 3ms - see figure 3 in
http://www.rit.edu/~andpph/text-streak.html
> > 4.In auto mode, the shutter speed can vary infinitely, during the
> > exposure. Wouldn't this imply that the F280 must preserve enough
> > punch for the maximum exposure length, to keep the illumination even,
> > an amount not needed if the shutter speed turns out to be 1/2000. In
> > manual mode, though, the flash could be concentrated into the minimum
> > time, since it's known in advance. So why isn't the GN a little
> > different for the two modes?
> >
> Is there already enough comunication that the camera tells the
> flash about the selected shutter speed? -This would be necessary.
It's too late. The whole frame has to be exposed by the flash, so for
speeds over 1/60, the FP flash has to start when the first curtain starts.
Also, the flash contributes to the exposure, so it has to start, at a
certain intensity, by the time the first curtain opens.
The camera could tell the flash to quench when the 2nd curtain closes, but
apparently it does so only in manual exposure mode, not auto, probably
because it notifies the flash before the picture is taken and the timing is
handled differently than OTF quenching.
Tom
--------------- http://groups.yahoo.com/group/Olympus-Documentation
tOM Trottier, ICQ:57647974 http://abacurial.com
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awesome, indescribably magnificent world in itself --
Henry Miller, 1891-1980
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