Sigma AF 300mm doesn't work on 20D

[Parrot of Doom]

I have an old but quite nice Sigma 300mm lens. The autofocus doesn't work but the lens itself works nicely on my Canon EOS300 (film). However it won't work on the 20D, full stop. The DSLR just goes a bit loony and does nothing at all.

I can get the camera to work with the lens by taping over the contacts on the back of the lens, but that gives me no control of the iris (the camera just displays 00). Any ideas which pins control the iris?

[SamHH]

I don't, but I have read that Sigma can sometimes modify their old lenses to work with digital era cameras. Maybe it's worth contacting them.

[Simpo Two]

I got a Sigma 70-200 f2.8 that needed to a rechip to work properly with a D70. £75 from Sigma, and it's still one of my favourite lenses.

[Parrot of Doom]

Ouch. I think I'll manage without the iris then!

[taxboy]

I had to get my old Sigma 400 rechipped to work on my film EOS 30 - I only discovered the problem when a complete film came back overexposed as the iris doesn't stop down. If it will work on your digital camera you will have to realise that all shots will be taken at max aperture