Flash Delay Issues

For the bee-tracking system, we use a global shutter camera which means we can take extremely brief exposures, just capturing the time the flash is on.

Because there’s a delay between the trigger and the bulb actually firing (roughly 80\mu s) I use the PreDelay option to trigger the flash slightly earlier.

So to get an idea of the best combination of predelay and exposure time, I ran a grid search and found the mean of 3 photos at each combination.

Using just one Neewer TT560 flash (1/32 power).

It was quite noisy.

The average image value for different combinations of PreDelay (x-axis) and exposure (y-axis). On the far right the flash has been & gone before the shutter opens. On the left the flash hasn’t yet started when the shutter opens, but for the longer exposures they still capture the flash. An ideal spot will be towards the top (to minimise the ambient light from the sun): So maybe an exposure of 90us and a predelay of 65us.

The scattering of dots on the right are, I think, due to delayed firing of the flash (by a few hundred microseconds). Similarly the dark dots are either when it didn’t fire, or these delayed events.

Given there are 4 flashes firing at once, I guess occasional failures like this don’t matter too much, but it would be nice to resolve.