The continuous AF of any Pentax DSLR is pathetic, and so does the tracking ability over frames. If you have handled a Nikon or Canon upper level DSLR side by side, the huge difference can be seen.
What make things worse is the unable-to-keep-up C-AF will slow down the continuous shooting frame rate significantly when the camera is waiting for the AF.
Besides the slow and non-intelligent C-AF, the Pentax AF system is particularly insensitive and sluggish at lower light conditions, which makes even AF Single mode less useful and reliable under such condition. The worst thing is that for all Pentax DSLRs I have used, including the K10D, will never give accurate focus but Front Focusing under tungsten light, which is ususally the light source at low light.
As for your question on which focus point the camera will choose, the user can choose whether the central single focus point is used or let the camera to choose amongst the eleven points, no difference from Single AF mode. This design is very different from what Canon do, though. In continuous AF mode of Canon DSLRs and if multi AF points are activated, tracking shall always be started from the central point and the camera will track the moving subjects when they are moving out of the central frame.
In fact, if you activate all the 11 focus points and put the camera in AF-C mode, it is actually rather sluggish to be usable, for the K10D. If you compare with the Canon design in making the central point as the first tracking point in the beginning, you can see why Pentax's design can be even much more sluggish when all AF points are activated - it is actually impossible to have all the 11 points activated and doing the measurements at the *same* time at the beginning of the measurement.
Anyway, in short, even only the central single AF sensor is selected and only one frame is taken, the AF-C function of the K10D is still sub-par, as you mentioned. It will never fast and accurate enough to track fast moving subjects, especially for those randomly moving ones and/or towards or away from the camera.
Originally posted by Workingdog Hi everyone,
I've been following the forum for some time and have gained a lot of knowledge, so first off thanks for a great forum. I've done my research and plan on purchasing K10d paired with either the Tamron 18-250 or Tamron 17-50 for starters. My one reservation is Pentax's supposed below par performance with autofocus tracking of moving subjects. A lot of my photos will be taken outdoors in relatively good light with moving subjects. Should this be a concern for me? A deal breaker? I'm interested in hearing from folks who have hands-on experience with the camera under these conditions. Are there certain camera settings that can be made to optimize the camera's focus tracking performance; AFs vs. AFc, center focus vs letting the camera choose, etc.?
Workingdog