Testing for sharpness and that sort of thing

A while ago my K20D had a mishap and off it went for repair. Took two attempts, but repaired it was. Since then, I've never been that happy with it. For example, the katzeye split screen which used to work ever so well no longer agrees with the green hexagon, and neither seem to give the sharpest image. With AF lenses, they never seem to be as crisp as they used to be. For example, my 12-24mm is a super sharp lens but now there is an indefinable something not quite right.

Any ideas as to the best way of checking what is happening? Assume tripod, mirror-up, and cable release as given. Perhaps all my AF lenses need adjustment? The repair reset everything to factory defaults. Use the DA43 as the test lens? What about manual focus? Perhaps the screen needs re-shimming but how does one test an MF lens? And which one? The M85/2 is pretty sharp, or perhaps the K50/1.2 or M50/1.7?

Any ideas welcome. At the moment I am spending a fortune on film partly because I am getting sharper, better images than the K20D is giving me (but also because I love using my film cameras ).

Thanks, Kris.

K20 has a live view. use that

Excuse my ignorance, but what actually focusses on what and how?
I mean, if the focal length was nudged from a fall or other mishap the AF would still focus the optics, otherwise AF would never lock on, right?.
I'm good and ready to be proven completely wrong, but optically, as I see it - focus is focus regardless of something is a bit 'out', after all - if you manually focus, and it's sharp then this is the light which is hitting the sensor isn't it?

Womble:

1] on your tripod, use live view magnified to accurately manual focus ( Live view magnified on the K20D is pixellated but you can still focus accurately in msot conditions )

2] with moving anything exit Live View use the view finder to see if your split screen and/or focus confirmation agrees with this. if not then you'll have to either re-shim your screen and/or AF fine tune for your lenses.

Sledger: Sorry mate I couldn't understand a word of that

Never mind.

OK

I think that maybe you are overlooking that when focussing by any method the focus is (I believe) taken off the focussing screen while the mirror is down. Therefore if the screen has moved slightly during the repair what is sharp on the screen may not be sharp on the sensor as they no longer 'match'. I don't know if that helps (or is indeed correct).

Mike

Thank you,
That would makes sense if as you say it is correct - though it sounds quite plausible.
I'm not familiar with the way the camera works 'internally' - only the basics of picture taking from an operators perspective.
Helpful responses such as yours, Mike are always welcome - thanks.

Pentax ( and most other DSLRs I believe ) cameras have the AF sensor in the bottom of the camera. The centre of the mirror is half silvered and there's a secondary mirror behind the main mirror which directs some of the light down to the AF sensor. For this it doesn't matter where the focus screen is positioned.

this shows how it works

http://graphics.stanford.edu/courses/cs178/applets/autofocusPD.html



Manually focussing through the viewfinder and indeed the position of the focus screen is to be accurate.

The most accurate method of focussing ( Manual or AF ) is through the main sensor in live view as that's pure WYSIWYG

this shows how it works

http://graphics.stanford.edu/courses/cs178/applets/autofocusCD.html

Thanks..