Originally posted by kmanlaker this is exactly what I probably should have said to begin with --- that is the autofocus is fine with me on my k10d -- I am not a sports shooter and also I do not need 400mm 500mm type lens.
regarding the autofocus on the k10 -- it almost seems to me to be more accurate than my 5d was, it may not be as fast but it sure seems more accurate and that has to count for something.
kman
Quoted from another forum:
"First the boring stuff...
EVERY decent control system has a certain amount of hysteresis. Hysteresis
is created when a *small* distance about "perfect" accuracy is designated as
having sufficient accuracy for acceptable performance (this is often called
"deadband") and wherein active control is suspended. This is done to prevent
chatter or excessive "hunting". Chatter or excessive "hunting" greatly
increases wear, is hard on mechanical equipment and often creates excessive
noise and vibration. The autofocus in your camera is a type of control
system because most folks greatly dislike vibration and noise in their
cameras. Further, they would be greatly dismayed if the life of the bearing
surfaces wore out in months instead of decades; therefore hysteresis is
actually a good thing. You know that your AF system has built in hysteresis
because the lens does not continue to hunt (forever) on a stationary due to
sensor noise and continuous slight overshoots.
What the boring stuff means...
This means that your autofocus system will NEVER focus on EXACTLY the same
spot every time because the AF will stop when it determines that focus error
is within the deadband and therefore "good enough". Now DOF, in distance
units, changes with several parameters. This also means that the deadband,
in distance units, is different for every focal length, every maximum
aperture and every focus distance.
Autofocus is a convenience (and a great one at that), but it will never be a
substitute for critical manual focusing to accurately and critically
position your DOF about the subject. Some AF systems may be better than
others or have different features, but this is true for *all* AF cameras,
regardless of brand or model."
My understanding is that Pentax AF in the K10 and prior models allowed for a lot less
allowable hysteresis than what Canon was allowing. This made Canon AF faster, Pentax AF more accurate. I think they loosened up a little bit with the K20, it certainly locks focus faster than the K10, but I have found wide aperture performance to be a little soft from time to time.