Comment Re:Why are they using a Nikon lens on a canon? (Score 1) 171
I don't know what you mean by "old", but my father's old Canon (film) SLR's EF-mount lenses pop right onto my relatively new Canon EOS Rebel T2i (EOS 550D for you non-Americans) which takes EF-S-mount lenses.
EF-S is a subset of the redesigned-from-scratch EF lens mount from 1987 - still considered terribly modern 'cause it's fully electronic with no mechanical linkages between the camera and lens. New EF lenses are definitely still being designed, but yes - EF-S lenses won't fit on an EF-only camera, be it film or full-frame digital.
Canon's 'old' system is the FD lens mount, from 1971. The newer EF mount is almost completely incompatible - you'd need that overly-complicated-adaptor-with-included-optical-elements to get an FD lens to mount on an EF camera.
Compare Nikon's F-mount - lenses from 1959 are potentially mechanically compatible with the latest Nikon dSLRs, but there are huge compatibility charts describing which features may or may not work from any particular lens on any particular camera.