Flash problems with 20d

I am a very casual photographer and recently purchased the 20D. When I use my old mounted flash I have gotten many way overexposed shots even outside from a distance of 15-20 ft where the subjects' faces were practically white. Do I need a new flash that is dedicated to the 20d(i.e 580ex)? Thanks. :confused:

It sounds like your old flash is firing at full power. What's your old flash?

I've just bought a 20D and am trying to come up to speed myself on flash, having not used it before.

One thing I've already found out is that the digital SLR's need a flash unit compatible with E-TTL or E-TTL II metering. This is because TTL and A-TTL (one of which is probably used by your older flash unit) requires an in-camera sensor which measures the amount of light flashed back of the surface of the film. This is not relevent for Canon DSLR's so they do not have a sensor built in and cannot work with TTL or A-TTL.

My guess would be that your old flash does not support E-TTL or E-TTL II and there is this no auto metering happening. The flash is probably TTL or A-TTL copatible, but the camera is not! In which case you need one of the Canon units which the suffix EX as they support E-TTL.

Wish I'd known this before buying a 540EZ as a backup flash unit - it will have to stay on my EOS 50E because if my 580EX fails in action then the 540EZ will be no use on the 20D!