>From: "Mr. Bill" <[EMAIL PROTECTED]>
>
>Grega Fenko wrote:
> >
>
> > >3. Is the brightness of the flash constant or does my camera change it
>in
> > >different situations? Does the flash compensation affect this?
> > >
> > Brightness/intensity of flash is calculated (precalculated) for every
> > situation and camera metering system sends it to flash unit. Applying
>flash
> > compensation changes flash output for desired/set amount of
>compensation.
>
>No, no, no, the "brightness" of the flash is the same every time. The
>only way an electronic flash can vary it's output is by varying it's
>intensity.
>
I really wrote that strangelly.
Flash output is regulated by duration of the flash burst. It is 1.4mm or
less for 380EX. For all TTL flashes, as onboard flash on EOS 30 is camera
metering system cuts off flash when desired ilumination is achieved. By
seting exposure compensation you are telling camera how much uder- or over-
it should expose.
>When using a flash, the duration of the flash and the lens aperture
>control how much flash light hits the film and the shutter speed and
>lens aperture control how much ambient light hit the film. It is
>possible that the EOS flash has a fixed duration and basically the
>aperture controls the film exposure and the shutter speed controls ambient.
>
>I doubt that EOS flash is fixed duration as there are tremendous
>battery-saving advantages of using a short little pip (approximately
>1/30,000 sec) when you don't need much light.
>
That's when TTL steps in and cuts of flash.
Good light
Grega _____________
http://fenko.8m.com
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