GD> Seems to me this is the primary theoretical advantage of P-TTL
[...]
There is also a theoretical (and sometimes sadly real) disadvantage to
any pre-flash system, be it P-TTL, i-TTL E-TTL2, Minolta's one,
whatever... that is that it is slower than plain old TTL off-the-film
metering with film SLRs. And some SLRs used several (five) sensors to
measure the flash during the exposure, if I remember correctly. I have
myself seen the slowdown mostly with wireless flash, where it is
really slower (the subjects can even blink during the wireless
synchornisation phase), but others in the wedding biz spoke of it too.
It's not such a big issue, but _sometimes_, it can be a nuisance. Be
glad that Pentax and Fuji (?) still support plain "old" off_the_sensor
TTL, even with the other problems it brings with digital (sensor's
much higher specularity?). Of course the "problem" depends on how fast
the DSLR can swing the mirror (as the flash metering is done before
the mirror rises), so a superfast mirror-swinging machine would be
almost fine probably. But even on this list, I heard issues about
using preexposure flash metering for "candid" portraits.
Good light!
fra
