Don't know if this is just with canon mount sigmas, I assume that it happens with other mounts, but why do they have to be rechipped every once in a while? I understand that as Canon updates their cameras certain Sigmas will no longer work and need to be rechipped because they become incompatible but this is not the case with Canon lenses. I could mound the oldest EF lenses on the newest bodies without issues. Why isn't this the case with Sigma
Sigma reverse-engineers the electronics in their lenses (why would Canon sell the information to a competitor?), and Canon updates their electronics over time, thus a Sigma lens made for a 620-era camera won't work on a Elan II or a new digital camera.
So this means that in theory Sigma didn't get it right the first time. In other words the electronics are not duplicated. Canon does update their electronics but it does not render their older lenses useless. I was just looking at a Sigma and this little kink ruined it for me. Why would I buy a lens that may be useless 3 years from now?
Actually, Canon DOES sell its technology to other lense companies, but Sigma chooses not to buy. That causes Sigma to have to "reverse engineer", while the others (Canon, Tamron, Tokina, etc.) don't. Whatever technology Canon uses, it incoporates some method that allows older lenses to stay compatible. That technology either can't be duplicated via reverse engineering, or is heavily protected by Canon.
