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. Give it a second or two and it will settle down. This started only on the vertical pictures, but it has now spread to the horizontal pictures too.
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. If I had it to do over again, I'd put the money towards a lens designed for a DSLR, the electronics in this lens don't seem to be able to keep up, whether it's due to age or design I don't know.
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. I wanted a lens that served the purpose of not having to change lens as much this solved the problem but feel a Canon would have been a better choice but money wise this was a good investment for right now
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. Since it works well with this little defects, and my hands are strong, I will keep the lens instead of going through the replacement.
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. I really liked the lens at first but I've been noticing the more I use it that when I zoom in I get these dark shawdows in the top corners and it drives me nuts.
Summary: Having needed a lens with wide to narrow settings to save lens changes while on the move I decided after an article in photo plus magazine that this sigma lens was the way to go with limited cash to spend.I expected with the 18-200 there would be compromises but overall it was not nearly as good as expected.