Originally posted by MPrince No, HSM is Sigma's version of SDM.
I thought it was self-evident, but let me put my statement more precisely:
To the user, there is no difference between SDM and HSM. On AF, the focusing ring doesn't turn and the user can correct the focus manually at any time.
I'm very much aware that the underlying technologies are very different. So there is a difference to the user after all in that they have to expect the "Sudden Death Motor" to fail at some point whereas no such problems are known for HSM. But I was talking about the user experience, not the technology.