I've found the AF on the K-01 to be pretty snappy (at least on par with my old *ist D and K10D cameras) with the DA 40mm and DA* 55mm even if it isn't as fast as the other cameras I use. The FA77 is slower in low light with the K-01 but it's still usable and I personally feel like the image quality from the 77 makes up for some of the AF delay in low light. The following FA77 shot that I took of my son was taken while he was moving ... he turned his head just enough before I pressed the shutter button that his right eye (camera left) just started to move out of focus from the shallow DOF, but I still like the photo: