From what I read on the Sigma web site is this. AF
Mount HSM: Sigma, Canon(EF) and Nikon(D).
Mount: Minolta, Pentax. I believe the non HSM is for Minolta and Pentex. The HSM is similar to the Canon USM
. The following is a quote from Sigma's site " And with the HSM autofocus drive (Canon, Nikon and Sigma AF
models only) it is incredibly quiet and quick when autofocusing, and you can focus manually without having to disengage the AF
mode. In addition, this lens can be used with Sigma's two EX teleconverters for additional versatility (manual focus only)."
B&H photo has a good price on this lens. 900+change. I hope this helps...Artie