I do some cave photography as a hobby.
We have a problem where most commercial slave triggers do not work in our environments.
Slaves rarely trigger in dark caves, especially off of secondary reflections, when the slaves are hidden from direct line-of-sight of the main flash. We almost always want to keep the slaves behind rocks, or models, out of direct line-of-sight of the camera.
Most cave slave trigger designs I see have 2 or 3 filtered amplification stages for the trigger. They seem to have tuned R-C coupling between stages designed to trigger on the fast pulses from photostrobes, but not on regular changes of lighting leves or flashlights.
Any recommendations on how to change the sensor part of the circuit to use one of these tuned, multi-stage amplifiers?