Archived posting to the Leica Users Group, 2002/01/13
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At 1:13 PM +0000 1/13/02, Leica User wrote:
>I thought I'd mention the newer Canon EOS range of cameras which have what
>they call FP flash which allows the flash to synchronise at all shutter
>speeds (up to 1/4000th second on my EOS 50E - probably higher on the EOS
>1V).
>
>It just so happens that in the current edition of EOS Magazine, dated
>December 2001, there is an article which describes FP flash. Basically, the
>flash duration is extended to the length of the exposure, e.g. 0.25
>milliseconds at 1/4000th second shutter speed. This means, though, that the
>intensity of the flash is reduced so it's most beneficial for fill-in flash
>where the subject is not too far from the camera.
>
>Perhaps this could be how the M7 would work?
>
>Joe Chan
>Surrey, England
Sorry, but this doesn't work. 0.25 milliseconds of flash duration
would only give you _one_ very narrow strip of exposed film. If the
flash sync speed in the standard sense, ie, the fastest speed which
has the shutter completely open is 1/125 sec, then the total flash
duration even for the fastest speeds has to be 8 milliseconds, and
the pulsing of the flash gun has to evenly cover that length of time.
That's how the FP flash systems work, whether by Nikon, Olympus,
Canon and now, presumably, Leica. In the M7 case, with 1/50 as the
sync speed, the flash has to be on for 20 milliseconds. As even flash
is not instant on/off, but ramps up and down (and this can be
smoothed and controlled through both electronics and physical tube
design), the pulsing can be done in such a way that the flashes
produce a light that is even enough for these longer times. OTF flash
automation doesn't work, of course, but the preflash technique used
by some manufacturers can provide automation.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com
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