I thought I'd post a follow-up here and let y'all know how I'm doing.
To recap: I'm photographing my fifth-grade (eleven-year old) daughter playing volleyball and basketball. One of the reasons (well, rationalizations would be a better term) I used to justify the purchase of a digital SLR was the availability of higher ISO and the prospect of doing a better job at these sports photos. I'm pleased to say that the Pentax K100D is indeed taking better photos at basketball games than my otherwise wonderful old Canon Powershot S3 IS was taking. Here's
a link to an example of where I started - lots of noise and even then I was unable to freeze the action. The absence of shutter lag is a big help. And the K100D's camera's higher ISO capability is a help, too.
But now I have what I think is a good lens for the job: the
Sigma 28-70 f/2.8 DG EX. Well, two lenses, really. I also recently acquired a Pentax M 50mm f/1.4. This is a nice little lens. I'm enclosing one shot taken with each lens. The more dramatic shot with the clear V arrangement and the girls running right towards me was taken with the Pentax M 50mm. The other shot, with the girls running from left to right, was taken with the Sigma. Although I did get lucky a couple times with the Pentax manual-focus lens, I have decided that it does not really take significantly better pictures than the Sigma and is not going to work for me in the gymnasium as well. I find the 28-70 zoom range to be useful. And I just can't seem to do as well manually focusing any lens as I can with auto-focus, unless I have lots of time. Anyway, I'm happy enough with my gear right now and I'm grateful to those of you who offered your suggestions weeks ago when I started this thread.
Now I'm trying to learn to USE this equipment to take better, more interesting photos. I've discovered that most of the photos I take at these games look like most of the others - cliche and boring. I've attached a third shot, of some girls down on the court struggling for the ball. It was taken with the Sigma: 28mm, f/2.8 @ 1/200s, ISO 1600. It's not a gem but it has a bit of drama to it and it's a break from the routine. I may yet crop it a little tighter. This sports photography stuff is a challenge!
By the way, a number of you suggested lenses with longer focal lengths. I think I'm doing okay with the 28-70. I tend to park myself right on the sideline at the corner of the court near the basket our team is trying to score in. I miss a few shots at the far end of the court when we're playing defense. Maybe a 28-110 would be better, if it still had f/2.8 throughout the range. But it's nice to be able to go wide when the players come back down where I'm waiting. More than once I've had to think quick to avoid getting hit by a ball or a player (or a referee who's backing up). But it seems to be good to be close to the action.
Will