I have a (cheap) friend at work who has a Canon Rebel something DSLR and a 15-year old Metz flash. It won't work on his Rebel, so he wants me to bring in my Nikon flash so he can see if there is something wrong with his camera. I'm reluctant to do this, as I have no idea about the compatibility between Nikon flash and Canon DSLR's. Is there any risk in this? I have a SB 800 and SB 600.