Originally posted by Kobie
How dirty is the PDAF sensor? (under the mirror).
Have you ever cleaned it?
Try a rocket blower but don't touch anything with the tip of the blower.
PDAF has it's own focus sensor, CDAF is on the sensor which is why there's a difference.
Yes, they have been cleaned, many times.
I have a clear understanding of the differences between CDAF and PDAF, which was really the whole point of my original message...if it's the lens that's at fault how can CDAF not be back focussing as well?
Cheers,
Terry
---------- Post added 12-11-19 at 01:52 AM ----------
Originally posted by pschlute
First and most importantly, to assess and front or back focus you need a rigorous testing regime. So...camera on tripod/natural light/proper test chart/ remote or timer trigger. Equally important is you need to do 10 tests each time making the camera work to focus from close or infinity setting. PDAF is just not accurate enough for you to rely on a single AF test. If you get 8/10 identical and can adjust for that you have done well.
I have a very rigorous testing regime, I do understand the need for that, but of course one can never rule out a testing error, which is why I have repeated the tests over an over again, 10 is a small number!
Quote: Live view focusses on the sensor itself using CDAF. It does not use the PDAF system at all. You cannot , and have have no need to adjust the AF when using LV.
If after a proper testing regime you find that PDAF requires AF/FA in excess of the +10/-10 allowed in the menu , you can send camera and lens back to Pentax for free adjustment back to zero.
Everyone seems to have overlooked the fact that both camera bodies have progressed from moderate back focus to a state which is unable to be corrected, and THAT is what has led me to think it must be the lens at fault...hence if that is so, how can the CDAF be OK and PDAF not?
The corollary of course is that both camera bodies have progressed in back focussing at a similar rate, which may be the case, but a low probability in my view.
Cheers,
Terry
---------- Post added 12-11-19 at 01:56 AM ----------
Originally posted by BigMackCam
If your testing and calibration regime is beyond reproach and consistent, and you've noted equivalent changes in AF fine adjustment for the same lens with more than one body, then theoretically it's possible one or more of the optical elements in the lens has shifted, which might be a result of various scenarios. Definitely something to get checked by your service centre - and be sure to give them the same information you've provided here.
OK, that's an interesting observation.
If that is the case, would CDAF still be able to achieve sharp focus while PDAF can't?
Cheers,
Terry