It's really good. In my experience Pentax AF has lagged behind Nikon and Canon in terms of performance, but the AF in the K5 is far superior than any Pentax I have ever used and on par with other brands. It's very good in low light with no hunting. It's also really good in terms of noise reduction at higher ISO settings. The interface is really well designed giving access to most features via a single button rather than having to dig through page after page of menu screens. This camera is light years better than the K10D; I should buy Katerina a gift for breaking it.