I am trying to use the Sigma 70-300 APO Macro lens on my EOS 300D. Firstly I get the Err99 message and the camera won't start.
If I operate the lens on my EOS 500 film camera and then transfer it directly to the EOS 300D it is usually OK. Equally if I try another lens first (not the 18-55 EF S) and then the Sigma, it may work.
Any ideas gratefully received.