Why do you need a TTL trigger?
I found out soon what was the problem: it wasn't a strobe with Digital TTL capabilities. So it simply wasn't able to work with digital e-TTL protocol. I started to think about a solution, but it took 10 years until I thoroughly examined the i-TTL communication of Nikon DSLR cameras.
Why did I need TTL? The reason is simple. When I took macro shots or especially when there was some kind of action it's quite difficult to take a photo with a manual strobe setting. For example, when I saw an exciting macro subject and it moved just an inch away, I often needed to change the settings. Or when I wanted to try different apertures to change the depth of field and I used F2.8 instead of F16. So I had to change the power level manually for both strobes while I was calculating: different ISO settings, different subject distance, different aperture. Maybe I was lucky and the subject would stay in the same perfect position for a few minutes until I could make the perfect shot. But usually, the tiny animals weren't that helpful models.
The TTL (Through-the-lens metering) in itself is similar in the different cameras. But every given camera model has a specific protocol. There can be one or more pre-flash of the same level for metering.
When you push the shutter button the camera sends a signal to the TURTLE to make a pre-flash. The trigger will send a signal to the external strobe by the LED via fiber optic cable connection or by the sync cords' pins (GND, QUENCH, TRIGGER). The pre-flash illuminates the subject and the camera do the metering through the lens. Then the camera sends a signal to the TURTLE so the trigger can control the main flash to make a perfectly exposed photo without any manual strobe adjustment. It can handle both first or second curtain setting.
As an underwater photographer, we have many things to pay attention to. The diving conditions, the air in the tanks, our buddy, the dive guide, the currents, we have to find the exciting subjects, we need to find a good angle, we have to think about the camera settings, move the strobes, etc. Anything which can make taking photographs easier helps us. That is the reason why we think you would love a reliable TTL trigger.
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