#7. "RE: Off camera wireless trigger with TTL-BL functioning?" In response to In response to 0
Richmond Hill, GA (Savannah), US
>Is there a wireless off camera trigger (non-cable) that gives >TTL-BL for the Nikon D600, D4 ?
No, there is no way to use the TTL-BL mode with the flash controlled wirelessly.
The reason for this can only be understood once you understand the way TTL-BL works. TTL-BL uses the internal camera light meter to measure the brightness of entire frame (or most of the frame when using Center Weighted metering), and sets the flash power based on the distance to the subject as reported by the lens, to make the subject brightness equal to the overall frame brightness.
If the flash is off-camera, there is no way for the system to know how far it is positioned from the subject. Also, the system has no way to know which way the flash is pointed. Therefore, the system has no way to determine how much flash power is needed to balance the subject to the background.
Consequently, only regular TTL is available when using speedlights off-camera - except - when using a flash cable. TTL-BL is available when using a flash cable, because the flash thinks it is still mounted in the hot shoe. However, to get proper exposures you have to be very careful to keep the flash at the same distance to the subject as the camera, and keep the flash pointed generally in the same direction as the camera. If either of these two things is neglected, the flash power is usually set too high, overexposing the subject.
This also explains why TTL-BL doesn't work well when bouncing the flash or using a bounce card. When the flash is not pointed directly at the subject, the distance to the subject is not used. Instead, the monitor preflash is used, and that is very unreliable in bright ambient conditions.