Love this lens. I purchased this lens as a compliment to my 2 Pentax kit lenses (DA L 18-55mm f3.5-5.8 and DA L 55-300mm f4-5.8 zooms) that came with my k-x camera. With this lens, 55mm is right in the middle. I also wanted a lens that would would work well with my old Pentax ME-Super film SLR. The filter size is 58mm (same as my 55-300mm).
This lens is silver & comes with an aperture ring (needed by the ME-Super) and the ring has an "A" setting (needed by the k-x). I believe, but am not absolutely 100% sure that the lens is designed to accommodate the full 35mm frame of the film camera (I have not yet gotten film picsdeveloped yet, though some other reading led me to believe that it is), but I have been very impressed with the digital pictures I've gotten with the k-x and this lens has replaced my 18-55mm kit as my "default", "walk-around" lens! It works well for portraits, closeups, & sunsets. The pictures are every bit as good as the kit lenses, though it's sharper at low F-stops that the kits, IMO).
It takes good pictures even wide open. So far the only thing I've noticed is a very slight chromatic aberration if I blow up the image to full size on my 21 inch monitor (edges being slightly reddish on on side of very bright contrasting objects), but otherwise unnoticeable (unlike the newer kit lenses, the digital camera is not able to do chromatic or distortion correction for this lens - they are forced off in the settings) !
The lens focuses very fast. The focus ring is nice & smooth. Manual focus is easy and autofocus works well. The zoom ring is a bit firm, but it will stay where you set it and definitely not "walk" while the camera is pointing down! The only stupid thing is the front of the lens rotates with the focus ring, so when using a polarizer, one must focus first, then rotate the polarizer. So far, this hasn't been a pbm for me when using a polarizer. The lens is light weight (mostly plastic, hence the 4-stars), but feels snug and well-built. It's not a "pro's" lens, but for me, it's more than worth the $29 I paid for it! There is one thing terribly wrong though (lol) - mine came with a "Canon" lens cover?! Oh well, fits perfectly though! For photo samples, visit my flickr site at [...]. Many recent pictures were taken with it and it shows up in the Exif data.