In another topic Rodd wrote "I've had issues with getting the TTL to work consistently. ..." Well, I had the same problems and changed to manual. However sometimes it would be just convenient to have a reliable TTL, for example if you play around with f/stops. Or if a shy creature retreats if you fumble with strobe settings.
Today I did a series of test shots with TTL. Before I started I used the small camera strobe alone (no housing) and an Olympus FL300R; with both strobes exposure was 100%perfect.
My test setup for the u/w strobes: Camera was set to "Fill" flash, no flash output compensation. I used spot, center weighted and ESP metering, I used low ISO and ISO 400. All pics taken with an Oly 60mm macro lens. I shot with an Inon Z240 Type 4 and with a YS110a, both triple-checked for the correct settings. And single strobe only to keep things simple. I used two different fiber optic cables, both 3rd party products.
My results: No reliable TTL results. Sometimes the pics with f/stops 2.8 were okay, sometimes completely overexposed, f/3.5 to f/7.1 were mostly okay, sometimes overexpossed; f/8 to f/13 sometimes okay, sometimes overexposed. In the range from f/14 to f/18 results were mostly okay, f/20 and f/22 were underexposed. (I checked- wIth manual output at f/22 the pics were completely overexposed, so the strobes had enough power.)
I changed the in-camera strobe compensation to plus and minus - this had little to no effect.
Then I remembered that I have an old Heinrichs-Weikamp TTL-Converter. So I used an electrical sync cord at the strobe and hand-held the converter in front of the housing strobe holes. Guess what - TTL was okay! In camera strobe compensation worked flawlessly. I could even get an old YS120 to work with perfect results.
But using this converter in the field is not a real option too bulky, and ofor one strobe only. What could I do to get TTL working with fiber optic cables? I am a bit reluctant to buy an expensive genuine Inon or Sea&Sea cable only to find out that this does not help... Any idea? Does it make sense to buy a THICKER TOS link cable (2mm) and use this with the connectors (should work if I strip off the coating)? Any other idea?