> William Sommerwerck wrote:
>
> > The guide number listing for Super FP mode shows that the square of the
> > guide number divided by the shutter speed is a constant at all shutter
> > speeds. This means that, even if the duration of the Super FP flash varies,
> > it has _no_ effect on the flash's output.
>
> Right.
>
> > So the question of _why_ there is a difference in duration remains.
>
> To save battery power.
Non-sequitur. How can you have constant flash output AND save power [sic -- you
mean energy]? The energy has to come from somewhere. Equal exposure requires
equal energy taken from the battery.
> > If you don't mind my getting a bit off-topic, the same issue could be
> > raised about non-flash OTF exposures. At auto shutter speeds above 1/60,
> > the exposure is actually determined by the light striking the right side of
> > the film plane (as seen from the back of the camera)! At
> 1/1000, less than 3mm's width of the film-plane area determines the exposure.
>
> No, with speed higher than 1/60s it is off the curtain, not off the film.
> Exposure is determined at the start of exposure by light
> reflecting off the curtain not off the film.
Whoops! Duh... MAJOR MISTAKE! 50,000 lashes with a wet noodle. I completely
forgot that the first curtain is patterned. Sorry about that...
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