Originally posted by deuces Have both. They're both stunning! The decision here is not price or IQ, but really speed and focal length.
Both very sharp, and with great colors.
Having both as well I would agree with deuces' comment. As said they are different lenses only because of the focal length ranges. Some practical examples, if I could only take one lens with me on a hike I'd take the Pentax 16-45mm. Usually I carry the Tamron as well as a closeup lens. On the other hand if I was indoors and taking more portrait range shots I'd go with the Tamron 28-75mm. Most of the shots (
here were taken with the Tamron 28-75mm/2.8 any at 77mm shot with the FA 77mm Limited. The shots in
this gallery are mixed. Any close up shot or with a wide aperture were taken with the Tamron (if memory serves that's the first 2 and the last picture). All of the wide shots are certainly from the Pentax.
Some slight differences I have seen between the lens that might sway your decision. The Pentax is not as good at close up shots as the Tamron. Although the Tamron is not a true macro lens, you can get very good results at close range (say < 1 foot). I think the bokeh of the Tamron is smoother than the Pentax, but this could just be a function of a wide aperture. On the shorter focal length side of each lens (wide), under extreme contract conditions, I find the Pentax displays more purple fringing than the Tamron. That said it's rarely an issue in my hands. For my self I view these lenses the same quality with complementary uses.
In short you can't go wrong with either lens and, as with any lens choice, it really depends on what kind of photography you can use. For the money I think they are some of the best K-mount zoom lenses you can get.