Okay, when I bought my Pentax K20D, I was given an "upgrade" from the kit lens (pentax 18-55mm 3.5-5.6) to a Sigma 18-50mm lens. I was intrigued at the idea of having an "upgrade lens". I only own one lens that didn't come as a kit on one of my pentax cameras. So, my K20 arrives, and I start shooting. I am EXTREMELY dissappointed in this Sigma lens. The crispness in my photos dropped to below what I would pass off to clients. So, I tried opening up my aperture a hair which I've been told that the middle ground on your aperture is the crispest place on your lens (don't know if I worded that correctly) and still saw terrible results. My actual first fear was that it was the blame of the K20D. I had read every review of this camera, and had a hard time believing that it could put out such bad photos. Plus, we all know, that your glass is more to blame for good or bad photos than your camera body. Well, Saturday I shot some senior portraits, and today I did some Maternity shots. This was my chance to test out the lenses, and cameras and decide what the issue is. The decision . . . my kit pentax lens is far superior to the Sigma lens that the camera company "upgraded" me to. Pentax wins out again! Now I'm saving up for my 50mm 1.4! yeah! So, here's the Sigma Lens (these are SOOC straight out of camera, enlarged to see detail) and here's the Pentax lent (also SOOC, enlarged for detail) what's your opinion?