Summary: I've only taken it out shooting twice since i got it - once to the zoo and once to a community event. I'm very satisfied with the photos right out of the camera with it, especially photos of people. Very little post-production work was required, which saves me hours over a lens with less appealing rendering. Definitely heavy and long enough that it benefits from support.
Summary: Was not happy with this lens. I may have had a bad copy but was disappointed with sharpness. Was big and heavy. Sent it back and got the way less expensive 55-300mm and I like the result better.
Summary: I installed the lens on my K-3 and every shot has created a smile. I have great lenses but none I like better than this one. I's a bit heavy but by turning the tripod mount sideways I can hold it very well. This lens and the K-3 work flawlessly together and I'm getting great results. The lens was expensive but after seeing the pictures I realized that the price I payed was a bargain.
Summary: Excellent image quality. Very sharp , beautiful color. Smaller than a 70-200 (this is 67 filter size and shorter without the hood) but covering a bit more range. F4 work fast enough for outdoors daytime but consider this lens is very well build and weather resistant WR so ypu can shoot in dust and rain without worries with much better image quality than other consumer zoom on this range. No problems with sdm af.
Summary: I have had this lens for about a month now. This is a versatile lens, covering a wide range and well. It is well constructed and rated AW (All Weather as opposed to merely WR). If you are reasonably strong and steady, you can hand hold it with amazing results. You may need to increase the shutter speed to reduce shake. It is heavy(more than a kilo!) however for its range and max aperture it is not imposing (only if you add the lens hood and extend it to 250mm).
Summary: I loved my 50-135 f2.8 Pentax for my K-5 Pentax camera. It really grabs a good image amazingly easily. So I thought I needed a bigger zoom, read the positive reviews and ordered a ("like new") 60-250. For several months I have been disappointed with the results from this lens. Then today I decided to check the auto-focus and found it is not quite accurate. Fortunately there were several on-line articles about calibrating the K-5 for individual lenses.