I had the same thoughts as what Bruce has already written, so, no reason
to repeat. The only difference is that I believe preflash cannot be
disabled in digital-era *-TTL. At least not with PTTL, and I don't think
it was possible with the Nikon D300, D700.
That preflash is the essence of how D*-TTL works: it is used for measuring
the exposure.
So, I'd expect that the only way to disable the preflash on a *-TTL flash
is to switch it to a non-*-TTL mode. That could be the legacy-TTL mode
or a "manual" (i.e. using the specified level of power output, or
just full-power-and-length) flash mode.
I don't know any if any camera has that implemented either of the two for
the pop-up flash. I doubt, but who knows, maybe...
An additional thought of what to consider:
1. You can get a cheap simple non-TTL hot-shoe flash (with a
low trigger voltage!) as a trigger (for each of your students' cameras)
or
2. You can probably get a *-TTL-aware slave-trigger to the lights,
connecting it via a PC-sync cable. (I have not checked if such triggers
exist, but I would expect they should.)
This way you don't need anything added to the students' cameras.
HTH,
Igor
Mark Roberts Mon, 23 Apr 2018 06:47:18 -0700 wrote:
Bruce Walker wrote:
Mark, what you experienced is one of the reasons I don't recommend folks
try that popup flash triggering hack. The other of course is the light
pollution from the popup flash getting into the shot and flattening the
contrast.
Understood. But when you have to have groups of 3-5 students shooting
at once and only one radio trigger, well, optical triggering it is.
But you have at least two possible issues with each student's camera: the
x-TTL pre-flash, and the "red eye reduction" pre-flash. Either or both of
these might be enabled in any given camera.
I did check to make sure red-eye reduction was turned off. I didn't
see any options for turning off X-TTL pre-flash. I may have missed it
(we had a lot of different cameras, obviously) or it may not have been
an option in the very cheap DSLRs the students had.
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