I have an old camera flash unit, about 15 years old, a real good one, hardly used! will it work on a new digital SLR or do I have to buy one that`s compatible Thanks.
I can't give a definitive answer, but it's probably yes. Why not just try it?
Some digital cameras have settings for 'slow flash' or something like, which I believe is something to do with using 'normal' flash guns with them. (Mine does) It synchronises the camera 'shutter' and flash, somehow.
The connectors are the same, and I can't see that they would have done this if it were not to allow interoperability.
If it has a hot shoe - a connector wire isn't always needed. A hot shoe is a square plate on the bottom of the flash with two or three recessed balls in it that connect with the flash mount at the top of the camera. The flash may have an auto function. Or you can do it manually - but you need to know distance to the subject - information that not all modern cameras show. You can then adjust the Aperture and the shutter speed accordingly. They will "talk" to each other and you should still get good results. However - I'd use the built in flash 99% of the time - it's a perfect combination the old flash unit might be OK for fill-in flash or if the subject is out of the built in flashes range - something you need to check with the instructions of the old flash.