Heya. I have inherited a venerable YS01 strobe which has just two power options - ON or TTL. It is being triggered by a simple fibre-optic cable attached by Velcro sticky pads to the Ikelite Compact housing and in front of the strobe trigger sensor. I'm getting decent enough results with ON (i.e. manual, full power) and playing with distance, strobe positioning, ISO, E/V, f/number and shutter speed, but don't notice any difference when I put the strobe in TTL.
My understanding from the strobe manual is that in TTL the strobe assesses the scene and adjusts the flash light output accordingly, and if it cannot decide, it just punts out of full power. Question is, if it does decide to vary the power from full, what aperture and shutter speed settings is it assuming the camera is using? There is a guide number chart in the manual - is that what I need to refer to in order to set the camera up? Clearly the strobe is not getting this information down the fibre-optic cable.....all that is doing is telling it to fire.
It's a question I get asked often by diving guests where I work, so it would be good to know what TTL does in this set-up.
I assume also that using a bulkhead connector between the camera's hotshoe and the strobe allows exposure information to be shared with the strobe? (my camera does not have a hotshoe, but I'd like to know anyway for future purchases). Thanks