Summary: I used this lens for the last year or so and have taken approx. 15k images with it. Mostly portraits, but some action shots. I've noticed at first when you turn the camera on it's side to get a vertical picture, the image would "shake" in the viewfinder.
Summary: This is an older lens and doesn't always work well with my Nikon D5100. The autofocus often gets 'confused' and goes more out of focus than in, forcing the use of manual focus. Does not fire nearly as fast as my Nikon lenses when shooting sporting events.
Summary: I am somewhat pleased... Lens kinda slips down when focusing in and out. Like its dropping. I ordered 2 filters which were suppose to fit it and one if them was too big. Thought I was getting a 62 but sent a 72. Other than that I feel the lens is pretty good.
Summary: The picture it took is sharp and the focus is good. But it needs some efforts to zoom the lens. It feels like something stuck (I released the lock switch) inside. I can not do a continues zoom smoothly.
Excerpt: The HSM is quiet. The optics of this lens is OK. I compared the bokeh of this lens with my Pentax DA* 50-135mm at f=2.8, the Pentax one's bokeh is significantly smoother than this Sigma. The biggest problem I had with this lens is the slow focus at 50mm when aperture is opened to 2.8.
Pros: Easily Interchangeable, Strong Construction
Cons: Blurry Focus, Heavy, Poor in Low Light, Slow Focus
Summary: really looked forward to getting this lens but after having it for a little while I'm not so excited about it anymore. I have an older nikon d40 camera and was hoping getting a nicer lens would help with the pictures and give them a fresher look, until I get my upgrade camera.