TTL is used to generically refer to automatic Through The Lens flash. iTTL - Beginning in 2003, with D2H and D70 with SB-800, to the newest recent current models (This includes the F6 film camera). The iTTL flashes are SB-400, SB-600, SB-700, SB-800, SB-900, SB-910 and SB-R200 (as of today, 2013). There are also several third party flashes compatible with the Nikon iTTL interface (and a handful compatible with the wireless Commander Remote mode). The iTTL metering is done by the camera system, and the flash simply has to accept the proper power level command. Yongnuo YN-622N supports iTTL.