Summary: I have been shooting flowers and small animals for many years. I have used non-Pentax but high quality macro lenses, and extension tubes with good results. Last year I bought this Pentax 100mm 2.8 Macro, the Pentax ring flash, and the new K-7 body. I started photography for fun in 1973 with a Konica; I then switched to a Minolta in College. I worked part-time as a photo stringer for the local paper and Associated Press.
Summary: For the most part I'm very happy with this lens. It's pretty sharp wide open and produces tack sharp images up to f11. f16 is good but by f22 there's noticeable softness. Diffraction kills this lens at what is a very useful aperture for depth of field. Forget sharpness at f32. The lens is very compact and light for a macro. That's good. It lives in my bag and I use it often. Color is neutral if a bit low in saturation.
Summary: This lens is hard to review since it does have some significant weaknessnes so let me get those issues out of the way: 1) Not a good low light performer. Don't think you are going to set this up in a low lit room and a tripod and get the AF to cooperate unless you provide additional light. You will have to manual focus. 2) No AF limiter, which wouldn't be a problem if 1) wasn't a problem.
Summary: My first impression of this lens was that it was much smaller than the pictures make it out to be. Only about 3 inches long by 2 inches in diameter. But boy does it make your photos pop. I've been reading a lot of reviews about the new Pentax K7, considering upgrading from my K10D. But one review I read, criticized consumers for wasting time always upgrading their camera body, when what really matters is the glass. Well, I can say, that guy was right.
Summary: I really love this lens, The closeups are great. Iv been into photography for years and always wanted a macro lens, and I don't regret getting this one. The sharpness blows me away. I do recommend this lens.
Summary: I have made close-up photos with Nikon 60mm f/2.8 and Pentax 100 f/2.8. In comparison, the Nikon 60mm has better resolution. However, I much prefer the 100mm in real life. The Pentax 100mm and other 90mm and 105mm macro lenses allow me to be much further away from the insect so that it doesn't get frightened and move away. The Pentax 100mm is small and light for a macro lens.