I have a Canon 20D and just inherited two older speedlight units: a Canon Speedlite 199A and a Nikon SB-26. I'm new to photography, so haven't used any sort of external flash before. The Canon is a 1980's era flash for a Canon A-1 film body and has a manual exposure dial on the back. The Nikon is an electronic flash from a 1990's era Nikon film body. I had read that the trigger voltage for older flash units was different and could potentially damage the 20D's electronics, so I haven't tried mounting the Canon yet. I'm also not sure the Nikon's electronics were designed to work with anything manufactured by Canon. So, the bottom line is, are these flash units at all useful for my 20D? Can they be mounted directly on the 20D's hot shoe or perhaps be used as external slave units? Thanks in advance for any input you may have.