I read an article sometime ago comparing a one pass AF used by N/C and two pass AF by Pentax. While 2 pass is slower, it's more accurate. Something similar like the manual focus era, you will focus back and fore to get the sharpest focus in the viewfinder... I can't find the full article but saw this post and I cut/paste here.
"The second interesting suggestion comes out of a post where it was explained that shooting can get tripped up by the autofocus because unlike Nikon or Canon, the Pentax system seems to do a double-check of the focus after a first guess. The camera won't fire until this is finished. Nikon and Canon just do the one pass, and this leads to quicker, yet sometimes innacurate focusing.
The poster went on to say that this can be circumvented by putting the camera in AF C, and taking the picture between the first focus, and the double check as you can trip the shutter at any time in AF C. He found that the Pentax system was correct the first time as much or more than the Canon/Nikon cameras he compared it to.
A setting in the Custom menu for the AF C or AF S to do only one pass, and calling it "AF Hi-Speed" would open that choice. People would realize it could be less accurate, but a welcome choice to some complaining about AF speed."
"The second interesting suggestion comes out of a post where it was explained that shooting can get tripped up by the autofocus because unlike Nikon or Canon, the Pentax system seems to do a double-check of the focus after a first guess. The camera won't fire until this is finished. Nikon and Canon just do the one pass, and this leads to quicker, yet sometimes innacurate focusing.
The poster went on to say that this can be circumvented by putting the camera in AF C, and taking the picture between the first focus, and the double check as you can trip the shutter at any time in AF C. He found that the Pentax system was correct the first time as much or more than the Canon/Nikon cameras he compared it to.
A setting in the Custom menu for the AF C or AF S to do only one pass, and calling it "AF Hi-Speed" would open that choice. People would realize it could be less accurate, but a welcome choice to some complaining about AF speed."
