D90 TTL question

Greetings, all.

I have a Nikon D90 and recently purchased a Nexus housing and Inon Z240 strobes with fibre optic cables. I'm still a little uncertain about how TTL works with my camera despite a fair bit of online research. I understand that by way of a preflash, the TTL feature will fire my strobe at the appropriate power, but what feedback does this give to my camera? I'm used to doing everything in manual mode with my old camera, so even if just the strobe power is automatic, this would be a bonus. Does the TTL feature allow the camera to chose the most appropriate aperture and/or shutter speed as well, or would that just be done by using Auto, A, or S modes in conjunction with TTL? I hope this question is clear; basically, I'm just not certain how much TTL takes out of my hands, for better or worse.

Thanks,

-David

You want to continue on with using full manual on your camera, set the fstop and shutter speed exactly as you would do if you were shooting with full manual everything. Then, the camera and strobe will talk to each other and shut down the strobe at the appropriate power lever for the proper exposure. The TTL will help you if you are off with your fstop selection but you are much better off to have your fstop set pretty much where you want it to be for the TTL and DOF to work its best.

In the film days, TTL meant the light reflected off the film was measured and the flash was turned off when enough light had hit the film for proper exposure..they Through The Lens (TTL) metering. With the advent of the digital days, things are a bit different. A pre-flash is done so the light can be measured in advance to determine how much flash to provide.

You can set the shutter/f-stop or allow the camera to do it, either way…but you have to realize the camera may not select settings that are best for the photo you want.

TTL results vary based on how much of the viewfinder is getting strobe lighting. If shooting a fish in open water with a wide angle lens, the fish might be over-exposed as the camera tries to light the surrounding water, for example. Whereas a fish next to the reef is more likely be exposed correctly as the whole picture is reflecting light back to the camera detector.

Thus many people use manual flash control for wide angle and TTL for macro work. But your results can vary based on what you do and how you do it.

Hope that helps.