#1. "RE: Slave with SB800" In response to In response to 0 Mon 31-Mar-08 11:39 PM by Wayne
iTTL is Nikons name for their digital DSLR flash mode that is metered for correct flash exposure through the lens (TTL) by the DSLR camera. TTL is Nikon-speak now for the older Nikon film camera version of this (which is very different). eTTL is Canons version (also different).
The SB-800 is quite a fancy flash, either on the hot shoe or as a camera control wireless remote. iTTL provides automated metering of the flash, which makes flash be a point&shoot system. But this makes mixing systems impossible. The Nikon DSLR auto iTTL flash system only works with the current new iTTL Nikon flashes.
Unfortunately, the cheaper third party flashes are incompatible with Nikons fancy system (actually, they are incompatible with any digital cameras automatic flash). Also older Nikon flashes are now incompatible with the iTTL on the new DSLR cameras. That means you have to put the fancy Nikon system into manual mode (or put the other digital cameras into manual mode), to work with the other flash that cannot do more. This means you (the photographer) are responsible for creating the correct exposure - it is no longer automatic, not point&shoot in manual mode. Which means then that both flashes might as well be this other cheaper system that cannot do iTTL.
Budget is one thing, but being usable is another. This is not to say the inexpensive non-brand flashes may not be good at what they do. But they do manual flash... they do not mix with Nikons iTTL modes with the Nikon flashes.