Real quick - the AF module is in the bottom of the camera; light passes thru a half-silvered part of the main mirror to a sub-mirror behind it and is reflected down into the AF module's optical system which splits the light into sets of 2 images and projects them into different AF detection areas. I.E. the images appear on pairs of line sensor arrays on the AF CCD. These are recently arranged in a 1-3x3-1 grid (the 3x3 are cross-type sensors, the 2 end ones are vertical line-type).
The position of the images along the array(s) are compared to come up with a defocus amount(s). This amount is used to know how much to spin the AF motor, which returns encoder pulses back to the CPU. Various algorithms and monitoring devices are used to determine which sensor area(s) to use, which line sensor in that area, whether there is enough light/contrast, whether the defocus amount will be enough to get lock, etc.
The multizone photo metereing IC is indeed above with the pentaprism, near the eyepiece.
Start with the lumo link as mentioned. Then go to Google Patents. Look up "Pentax AF".
I recommend US Patent 7496290 B2
& US 2006/0104621 A1.
Last edited by jmg257; 03-08-2012 at 07:03 AM.