Can I use my father's Sunpak auto 120 Flash unit which is about 20 years old with my nikon d40 digital camera? The trigger voltage of this flash could fry your D40. This page only lists a Sunpak Auto 120J, and the results are iffy:
http://www.botzilla.com/photo/strobeVolt...
New flashes, like the Nikon SB600, also have very sophisticated iTTL metering for better exposure results than the old gear. OMG is correct. It's not worth the risk. Buy a new SB-400 or some other smaller (cheaper) Nikon flash. The SB-400 is "only" $110 and it looks like a pretty nice unit. It was made to go with the D40. | 