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.