Hmm,
I am not quite following why the burn duration has to exceed the sync
speed. With the big guys I will be throwing away most of the light and
the duration is plenty long. It will be a bit tighter for the #6's
but still is plenty long even after the 10-15msec delay in FP mode.
The link to the pdf version of the graphs that is much clearer but is
not working.
I dug up John's post and he thought there may be some moderate
variability among cams with that delay.
So if the exposure is proper at say 1/125th, why won't the TTL metering
just close the shutter? I have no specific knowledge if the cam
electronics are such that it detects
something hooked up to the pc socket, but I bet it doesn't know. I
shoot one in manual just in case especially as Dr. Flash has
reservations.
Student of Dr. Flash, Mike
The numbers on the chart are too tiny for me to read them easily but I
do note that the time scale is in milliseconds and stretches over many
of them whatever the actual scale. A small portable electronic flash
may have a flash duration as little as a 1/50 of a millisecond or even
shorter. A big studio electronic flash might have a duration as long as
1 millisecond. All much, much too fast for the camera to handle in its
normal auto mode.
In order for TTL FP mode flash to work in auto exposure mode the flash
duration must be at least as long as the flash sync speed. For an OM
body that's at least 1/60 second or 17 milliseconds. If you look at the
ramp up/ramp down curves on those FP graphs you can see that getting
some stable light will take a while which is why the FP sync starts
ignition of the bulb before the shutter opens. Some additional timing
slop would probably also be desirable so I think I'd like to see a burn
time of 35 milliseconds or more. Even so I'm still not sure it will
work.
Dr. Flash
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