I dont use a flash, I only use available light I have from the grow lights. The Cobs I run are super bright, I shoot at the lowest ISO and adjust from there, typically I shoot manual mode and shoot around 1000th-1200th of a sec in the bright light (basically shooting in full sun) It can depends on what lens you are using also, a faster lens requires that you shoot at a faster shutter speed to let less light in , as not to blow your exposure . To help capture the frost, I play with shooting angles to let the light reflect off the trichs , or use shadows to help achieve depth to help with the affect.
Sounds good and makes sense to me. Newbie here so on the learning curve for growing/environment and also harvesting and checking trichomes and taking pictures too. Just finished my first harvest so just started new runs and don't have any frost yet. But will experiment with some veg plant shots in the tent. I have HPS and autocob lights so need to figure out how to work with them for pics. I do turn off the HPS when taking pics.