I started this thread last week and got some great responses. This is just a quick follow-up to let you know what happened.
Based on the recommendations I got here, I acquired two lenses (and sold some things). From KEH.com, I got a used Pentax M F1.4 50mm prime. And from Sigma4Less, I got a new Sigma 28-70 F2.8 EX zoom.
The Pentax M F1.4 50mm prime may be the best lens in my bag now, although it was the least expensive (not counting the kit lens, of course). I haven't yet done any real shooting with it, but the test shots are pretty impressive. This
shot of my wife on the couch isn't very interesting as a photo, but the sharpness is great. Taken handheld, in very low light. I didn't use this lens for this weekend's basketball game for two reasons. First, no zoom, and I decided that I would like to have that. Second, I find manual focusing difficult. Next week, though, I'm going to give this lens a try anyway.
So yesterday, I used the Sigma 28-70 lens to shoot my daughter's basketball game. This has a max aperture of f/2.8 throughout the range of the lens. The
whole gallery is online here, but I'm attaching one photo that's fairly representative. Had some white balance problems that I was not able to address perfectly in Adobe Lightroom. But I don't blame the WB problems on the lens. On the whole, this lens was a pleasure to shoot with and I'm quite pleased with the dimension of the results that can't be blamed on me or the camera. Definitely a HUGE improvement over
what I used to do with my Canon S3 IS; with the S3, I had to use its highest ISO setting (800, roughly = my K100D's 3200) and the results were very noisy. The shots I took this week were also a clear improvement over
the shots I took last week with the Tamron 18-200 F3.5-5.7 zoom. This week, I didn't have to shoot at ISO 3200 at all. I was able to stick to ISO 800 or 1600 and use shutter speeds around 1/400s much of the time. And as it happened, I seldom actually opened the lens all the way to f/2.8! I think the lighting in the gym was a bit better this time than it was last time, and that helped too.
As I said, I may yet find that the Pentax 50mm prime will work even better - if I can get over shooting everything at 50mm. However, I'm quite happy with the Sigma 28-70 F2.8 and think I can continue to grow with it for a good while. Now that I've sort of solved the technical hardware problem, I can really put my mind to figuring out how to take more interesting photos. Thanks again to everybody for your help.
Will