Excerpt: Since I've owned it for a couple of weeks only, can't really comment on the SDM durability, but for now it works fine. I haven't used other cameras with speedy lenses to compare, but for me, the AF speed is OK. Tracking AF feels kinda sluggish, though. AF works surprisingly well in poorly lit indoor conditions, though. But all that is irrelevant. Colors! Sharpness! Contrast! This lens well deserves the Pentax name and * rating, because it is excellent.
Pros: Accurate AF, Consistent Output, Durable, Nice Bokeh, Rugged, Strong Construction, Weather resistant
Excerpt: Bought this used. My K-5 Pentax is not noted for autofocus, so I was surprised as to how much better it focused with this lens. I really love a fast lens. Worked great shooting a christening in the a dim light of a church. Great for low light candid shots. Used lens was better than rated. Lens hood was not included, but Adorama sent one later after I called Customer Service. A true measure of a company is not just price, but service == Adorama can through for me.
Pros: Fast / accurate auto-focus, Nice Bokeh, Rugged, Strong Construction
Excerpt: This lens does everything I ask of it. It is heavy, but that helps me steady the shot. It is somewhat slow to autofocus, but I manually focus most of the time, and like to set exposure as well. Don't use it in auto mode very often. Would probably go with a faster lens for sports/action shots. I own many fine SMCP lenses from my k-1000 and Super Program film camers. Use this lens omn my K-20 with good results.
Pros: Consistent Output, Durable, Rugged, Strong Construction
Summary: Bought this lens with some trepidation because of concern over SDM failures. I "needed" a lens in this range and 3rd party lens makers really didn't have what I wanted. There were reports that the SDM was remodeled in 2012 (hope that was true and not industry talk) because of the failures in both the 16-50 and 50-135 models (shared the same SDM design). It was well into 2013 when I bought this lens.
If you are considering buying this lens dont hesitate, highly recommended.
9 June 2013
Summary: Purchased this lens to replace a 70-200 f2.8 which I found to be heavy and difficult to handle. I use a K5 camera with grip, this lens is just perfect, balances beautifully with this camera and the 50-135 focal length is so much more useful than the previous lens. The IQ is simply fantastic and has that certain quality that make images really pop. Autofocus on the K5 is fast, virtually silent and very accurate.