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Originally Posted by eeyore  the sigma 150-500 is the new one with OS and while it doesnt have the HSM of the 50-500 it is considerably quiter than the little bigma |
Sigma - Lenses This lens incorporates HSM (Hyper Sonic Motor), which ensures a quiet and high-speed AF as well as full-time manual focusing capability
Probably wouldn't be considering it otherwise as I AF to MF most of the time