Originally Posted by
rpcrowe
This incompatibility is the case with some "older" Sigma lenses and some "newer" Canon cameras. Sigma retro or reverse-engineers their products. In other words, when a new copy of a Canon camera comes on the market Sigma will purchase a copy and rework their lenses (if needed) so that the lenses will be compatible with the new model Canon cameras. This can leave an owner of a Sigma lens out in the cold if the owner upgrades his or her Canon camera to a new model. There is a possibility that the lens will not work with the new Canon since it was designed for an older Canon model.
I have an older Sigma 28mm f/1.8 lens which is a very nice low light glass EXCEPT that it cannot work with any Canon camera newer than the 10D. Sigma will rechip some older lenses free of charge to make them compatible with new model Canons. However, if they have replaced the lens in their inventory, they cannot or will not rechip it. This is the case with my Sigma 28mm f/1.8 which is a shame because it is a fine low light glass but, will only work with my 10D which has the worst high ISO capability of my three non IR cameras.
I understand that Sigma has a new system of converting their lenses over to new model cameras and I believe that it may be done without physically sending the lens to Sigma. However, I am not sure of that and I had such a bad Sigma taste in my mouth from the 28mm that I have never bought another Sigma.
BTW: I had an old Tokina 400mm f/5.6 lens which worked on all of my cameras and my 90mm f/2.8 Tamron which is an older version of that lens also works fine with all of my cameras.