Lukas,
Another way to calculate the distance is by measuring the loss of ligth.
IMHO this can be more
accurate, is easier to make and does also take in acount the loss of ligth
by a bouncing surface. So you can use the same basic system in normal- and
bounce-mode. This way you don't need an atomic clock.
Beside that, the flash-power is pre-regulated in steps of 50% of the
previous (1/1 - 1/2 - 1/4 - etc), so not highly accurate. (From 100% to 50%
flash-power the maximum distance changes from 16 to 11 meters, f/5.6, 80mm,
430EZ) but at the actual shot is cut-off at just the right moment by
(A-)TTL. For this system you don't need such an accurate distance-info, and
still use the right amount of flash-power for that situation. Thus the need
for lens-info is not there.
In case of E-TTL this might be different, but I think that also then the
measurement of the amount of reflected light by the object, is more
important than very accurate distance-info.
I many times had great result with this system but must admit I use many
times flash-compensation
by -.5 to -1 stop, and link my focus point.
I hope this answers your question
Drikus
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