Nikon’s new D4 and D4s DSLRs are unique in that they are the first Nikon DSLR to separate flash exposure compensation from the camera’s exposure compensation when using the camera with compatible Nikon Speedlights in i-TTL.
Previously, when in i-TTL and shooting in an automated mode like aperture priority, and you decided to use exposure compensation on the camera (which affects the ambient light), the change you made using the camera’s exposure compensation feature would also change the flash exposure on the Speedlight.
In effect, the two would be coupled together, if you wanted a different amount of flash compensation from that of the camera’s exposure compensation setting you would have had to calculate the two together and than change the Speedlight’s flash compensation accordingly.
For example, say you wanted to drop the exposure in the camera by one f/stop using the exposure compensation dial. The Speedlight would automatically drop the flash exposure by one f/stop too. You’d have to then add back +1 f/stop to the flash compensation to keep the flash exposure the same as before, but now your background exposure is lower by one f/stop relative to the flash exposure.
Yes it is an extra step, but if you shoot all the time in i-TTL, you would have gotten into the habit of making the necessary changes—and then you had to remember to reset both the camera and Speedlight once you were done shooting.
Confusing! Nikon thought so too.
The D4/D4s are the first Nikon DSLRs to separate or uncouple the exposure compensation from the flash compensation when using i-TTL in Aperture Priority, Shutter Priority or Program modes with a Speedlight (wired, using a Nikon SC-29 cord, wirelessly using the SU-800 Wireless Commander or another Speedlight in the Commander role, or on the camera’s hot shoe. It will not work when using a generic PC cord). With the D4/D4s, after making an adjustment through the custom settings, you set the camera’s exposure compensation for the camera exposure and it won’t affect the Speedlight’s flash exposure. Should you also need to alter the flash exposure, you can do so separately. We think this should make the whole process that much easier to remember and result in some amazing images where the flash and background exposures can be quickly and easily set.