Originally posted by Marc Sabatella You want better performance in low light, that all about one thing and one thing only: a larger maximum aperture.
Well, that and improved high ISO ability.
Assuming the K-x has even only one stop better high ISO performance than the K10D, the 18-55mm F3.5 - 5.6 can perform like a F2.5 - 4 (other than DOF). Some might say that the K-x has a
two stop like-for-like ISO advantage over the K10D. It might well be that the K-r and K-5 have a
three stop advantage.
It's not a coincidence that Nikon are putting energy in creating new F4 zooms... sensors have improved so much that other than for DOF requirements, large, expensive F2.8 zooms are often no longer required.