Well, what I wrote is my understanding having read as much stuff
as I can find. If it's incorrect, I would be delighted to know.
Seems to me this is the primary theoretical advantage of P-TTL
... the ability to integrate a preflash plus ambient exposure
with all the information provided by the lens (aperture, focus
point, etc) and body (multipoint metering pattern) to evaluate
more precisely the correct exposure.
Most of my flash work so far has happened with a non-dedicated,
Sunpak 383 flash unit relying either upon its built in
auto-sensor or a hand-held flash meter so I haven't had direct,
first hand opportunity to evaluate how much much of a benefit
P-TTL vs TTL vs any other stuff might be. :-)
Godfrey
--- Thibouille <[EMAIL PROTECTED]> wrote:
> I thought the were no matrix when using flash?
>
> > My understanding is that in TTL mode, the Matrix mode
exposure
> > evalution is working for the *ambient* portion of the light
> > metering, not for the flash metering. P-TTL allows an
integrated
> > preflash/ambient exposure evalution based on both metering
> > capabilities.
> >
> > I could be wrong, I'm certainly no expert on this stuff, but
> > that's my understanding. It makes sense as the Matrix
metering
> > evaluation is completed before the mirror swings up, since
the
> > meter sensors' light is piped through semisilvered bits of
the
> > mirror into the sensors at the bottom of the mirror box.
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