Originally posted by JHD From what I've seen, I'd hardly call the 50-135 "optically superior" but most definitely reliably inferior!
JHD, you've made your position quite clear, you dislike the DA*50-135 and like the Sigma 50-150. We get it.
Honestly, they're both great lenses. I recently had the opportunity to try both (at the same time) and I have to say that I would have been very happy to keep either one. Both are sharp and excellent lenses optically. If I had to give the edge to one optically, I'd probably give it to the DA* as I felt it had slightly more contrast wide open, although it was close. In terms of AF performance, the Sigma was certainly faster (as expected), but the margin wasn't quite as huge as I expected. In terms of build, I would say they are very similar, which is to say both are excellent in this regard.
Which brings us to reliability. Yes, there have been some SDM failures on the DA*50-135, no doubt. What are the chances that a given individual DA*50-135 failures? None of us have any clue that the real numbers are, including JHD. Same goes for the Sigma. I certainly suspect the failure rate for the Sigma is lower than the DA*, but I will not pretend to have any idea by what margain. At the end of the day, everyone has to assess their own ability to tolerate risk and make their decision from there.