Originally posted by bobbotron Using multi flash, with a relatively high hertz of 100
How you gonna do that?
I doubt your flashes can cycle that fast at anywhere near adequate power.
If you want to do multiple flashes at small intervals, you probably need some kind of sequencer.
That could actually be very simple and straightforward, though. Is your engineer friend good with simple digital circuits? It would be trivial with a couple of IC chips (and maybe a couple of transistors to actually fire the flashes) to create delays of a few milliseconds (and shorter or longer) between several trigger pulses.
I don’t know what the capabilities of your Cactus units are, but here are some relevant data from my Pentax AF540-FGZ (original version).
First, here’s the light intensity as a function of time for the flash set to 1/32 power. The total flash duration is about 100 microseconds. For more discussion of effective flash duration at various power levels, see my measurements of the AF540 from a while ago (
Flash Duration Measurements - AF-540FGZ - PentaxForums.com). From what I have learned from the Web, virtually all modern electronic flashes have nearly identical time-versus-intensity profiles. It is just the maximum amplitude that differs as a function of specific flash model.
I have not tried to measure the recovery time after such brief flashes - it seems pretty fast, but I rather doubt it is fast enough for 100 Hz flashing.
The AF540 does have a modeling pulsing flash mode, though. Here’s what the first few pulses of that look like - short, low power flashes every 20 milliseconds (50 hz flash rate) for a second. Note that the sensitivity level for these pulses is 1/10 that of the 1/32 power flash shown above - so not a lot of light output.
And here’s a close-up of the time profile of one of those pulses - quite short (even shorter than the 1/32 power level).
Maybe if you crank your sensitivity up, you can take advantage of a similar mode if your Cactus has that. Otherwise, as noted above, I think you will need a sequencer to get multiple images of your arrows at small time intervals by firing separate flashes.
Good luck! Sounds like fun (and have some sponges handy!)