Ann, You ask whether you can use a Nikon SB-22 with a Leica M6 TTL. I am using a Nikon SB-24 with a Leica M6. I use a wide piece of auto striping tape to cover all but the center contact on the hot shoe of the M6. I have checked the triggering voltage of the SB-24 and it is 9 volts, which I have found safe. Other older flashes may have trigger voltages of 250 volts+ (Vivitar 283). I set the SB-24 on auto. Of course, any and all mfrs, in this case Nikon and Leica would not own up to any responsibility if something goes wrong.