I have just acquired an excellent condition Sigma APO 70-300 for Canon. I think this must be their EF mount? Sigma says this lens won't work on a 7D because parts are no longer available. The EF-S mount pictured on Wikipedia, which is claimed to function on the 7D, looks identical to my Sigma's mount. Same number, arrangement, and shape of chips on both mounts. Has anyone tried the original EF mount on an EF-S mount Canon? I don't have a Canon camera on hand. If it will not function as-is on a 7D, is there an adapter for "old Canon to new Canon" that would let it function like the M42-to-Canon adapters do? Thanks for your help!