They are brand specific. Meaning Nikon will let you use Nikon's flashes and allow the two to communicate in other then M mode. I know few photogs who shoot Canon with a Nikon flash. Others use Metz, Nissin units. IF ttl is what you're looking for, then look for a 3rd party flash that is designed for your camera, otherwise go for a brand-name flash and enjoy it.prob anopther stupid question are they camera specific?