So you're getting a bit of noise at ISO levels that, with film, would be nothing BUT noise? Tsk. Noise can be dealt with in PP. My dad shot his very active kids (my sisters and I) using a TLR with (at best) a 75/3.5 lens. That was from my later childhood. Earlier, his TLR had a 75/4.5 lens. And he shot ASA 100 film. How? Shooting in adequate light, and social engineering. H'e softly call HEY, we'd stop momentarily, he'd shoot, and all would proceed. And that's how I shoot my grandkids (among other tricks).
Oh, these youngsters today, no patience! So you want to stop your kids movement, and ISO 3200 ain't enough, and Pentax glass is expensive? So don't just bid on A/M/K 50s. The Chinon-made Sears 50s are good at a fraction of the price. If you're not afraid to do a little Dremel cutting, you can easily mod Yashica C/Y and Olympus OM lenses to fit PK mount. Good Yashinon and Zuiko 50s are available, cheap. If you're not afraid of adapters, many great M42 Fifties can be found. The Yashinon DX 50/1.7; Meyer Oreston / Pentacon Electric 50/1.8; Super Takumar 55/1.8; Helios-44 58/2; many other good candidates labeled Ricoh, Mamiya, Petri, Porst, Vivitar. They ain't rare.
Other good fast focal lengths needn't be expensive either. I have cheap Vivitar 24/2 and 28/2 glass; and pretty inexpensive Nikkor 35/2 and 85/2 lenses that I easily modded for PK. I could probably save myself some trouble by just getting a Tamron 17-50/2.8 but I like fast primes.
You've had good advice on sniping. I'm a photo-gear-trader on eBay. I currently have ~225 lenses and ~45 cameras, and I've sold another ~110 lenses and ~30 cameras (to help pay for the keepers). Here are my rules of buying:
1) If it costs less than a sandwich or burger, buy it. If it costs more than a deluxe pizza, think hard about it. If it costs more than a good dinner out with your partner, ask here!
2) Bid low. Bid often. Lose 99% of auctions. Don't worry; another will be along momentarily.
3) Decide what any lens is worth to you. Bid no more than US$5 over that amount. Unless you go mad, of course.
Originally posted by Khoff2 F2.8 sounds about right. My understanding of lenses is that they produce the sharpest results at about 2 stops down from wide open. This is why I have been looking for a 1.4 or 1.7. Am I wrong in thinking this way or should I just look for a 2.0-2.8?
The sweet spot for almost all lenses on APS-C camras is around f/8. This assumes that you want edge-to-edge sharpness. We don't normally use fast lenses wide-open for such sharpness -- we want to grab images that are otherwise impossible. Most lenses sharpen-up considerable just 1 stop down, even less. An f/1.7 lens looks sharper than an f/1.4 because it IS sharper wide-open, with thicker DOF, but they'll probably be equivalent from f/2 onwards. Most f/1.4 lenses are very sharp, but only within a very thin DOF range.
So the basic trick for action shooting is to use a fast-enough shutter, nail the focus, and fix everything else in PP. Noise can be fixed, contrast and saturation can be fixed, sharpness can be fixed -- motion blur can't.
Have fun!