Today's state-of-the-art flash exposure system basically combines
the matrix metering with pondering the flash output according to focus
distance info. The pre-flash - required to compute main flash output -
is very short (likely less than 1/100 of the total power) and very
close to the main burst (possibly less 1/1000 sec). As it doesn't
significantly affect the guide number, even a small integrated flash
can employ this technology.
Anyway, all of the above may be crucial for photo journalism or
sports photography. To me it doesn't matter much as long as I still
have to compensate to avoid getting 16% grays out of deep blacks
tuxedos or pure white petals. And, as long as I have to think about
colour reflectivity, why not take the time and do the compensation
trick for too eccentric or too small subjects, or too prominent
foregrounds.
Servus, Alin
Boz wrote:
BD> I guess that what you really trying to describe is a TTL flash with a
BD> matrix meter controlling the flash burst. Of course, for such a thing one
BD> needs to compose the photo, then fire the flash once without opening the
BD> shutter, determine the matrix of constants to use for each metering
BD> segment, and then change the shot (flash once again and shutter also).
BD> There are two problems that I see with this, and both are bad but not
BD> enough to spoil the idea completely. First, your subject needs to sit
BD> still between the pre-flash and the actual flash. Second, you need a very
BD> powerful flash in order to be able to fire it twice within a very short
BD> time.
BD> One simplification can be done, however: use a TTL-flash matrix meter and
BD> couple it to the active AF point. Then you will at least have the subject
BD> that is in focus exposed the same as 18% gray. In this case there will be
BD> no need for a pre-flash.
BD> Just my "random" thoughts... Cheers,
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