> Could someone give me a one paragraph tutorial on the difference between
> e-ttl and a-ttl?
Disclaimer: Hope I'm right......
A-TTL uses a pre-flash from a separate near infra-red strobe on the front of
the flash unit to test out the subject illumination, this in my opinion
"can" sometimes be flawed in a situation where the flash head is tilted for
bounce lighting, (I think) the pre-flash goes off after the shutter is half
pressed. E-TTL fires a low energy pre-flash directly from the actual flash
tube itself to measure the subject illumination, this happens after the
shutter is fully depressed but milliseconds before the main flash is fired,
it's better than the A-TTL in theory because the effect of bounce tilting is
all accounted for. In an EOS-3 or 1V, 21 metering zones are also used in
E-TTL to better determine the "right" exposure.
I have personally had good and not so good results from both systems (3
years with A2E & 540EZ, 1 year with EOS-3 & 550EX), but I think the not so
good results are more from me not taking full advantage of the equipment
rather than the A vs E-TTL.
Lastly, the BETTL effect seems to be (far) more prevalent with the E-TTL,
again from personal experience.
Regards,
Ken
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