rjbenfield

Great. Thanks Tim. Rodd

Adam, Thank you. That was the key thing I didn't realize. Now it all makes sense. Fabian, Thank you as well. I agree, I think I'll preferentially use manual mostly, but nice to understand how TTL works for the times I may want to use it. Thanks all for your help. Rodd

I have an Olympus OM-D E-M5 in an Olympus housing with Sea and Sea YS-D1 strobes and optical synch cables. I've had issues with getting the TTL to work consistently. Sometimes it seems like its working and other times the exposure is completely off. The more I look into the problem, the more confused I get regarding how TTL works. It is my understanding that TTL works by sending out a pre-flash that the camera then analyzes to calculate the flash output for the on camera flash which then fires and that "flash" is transmitted via the optical synch cable causing the strobes to fire and also giving them information on how to fire to get a "correct" exposure. My questions are: Since the on camera flash is in the housing and not transmitted out of the housing other than via the optical synch cables, how does the camera calculate the TTL setting based on the pre-flash? Could this explain why the TTL exposures are so inconsistent? Or am I missing something very basic about how TTL works in this system? I don't have a problem shooting in manual but am frustrated in not being able to figure the issue out. Thanks for any information and suggestions you may have. Rodd

Hello. I'm a technical diver and UW photographer based in Guam.