I've been very impressed with the AF speed and accuracy of the K-7.
In bright light, focus hunting has never been an issue with previous Pentax bodies, but the focus travel speed was e.g. going from close focus to infinity for screw-drive lenses was a problem.
The K-7 does that travel noticeably faster.
The big difference in AF speed and accuracy has been in available light - all the typical indoor situations under artificial lighting, just bright enough to shoot handheld at high ISO. A lot of my photography is taken under such conditions. Interiors of homes and public buildings e.g. churches, halls, indoor events, night time functions on stage.
The K-7 will lock AF focus where the K10D and K20D will focus hunt for several seconds or just give up.
I previously considered the slow zoom lens nearly useless indoors for that reason, but with the K-7, I'm finding it very much usable indoors, combined with its pretty good high ISO performance.
With a large-aperture lens like the FA50 or DA70, available-light AF is a breeze.
The green AF-assist light only lights up in very dim light, or a dark/dimly lit object in an otherwise well-lit room. It has limited range - OK for portrait work, but not much of use in a big room. I've really only used it in conjuction with the on-board flash, which is rare.
With an AF540, the camera will trigger the Flash's Red Spot Beam. That bit is still slow and clunky, I wish Pentax could improve it..
Last edited by kittykat46; 07-22-2009 at 07:14 PM.