This discussion got me thinking...
Seems to me there are probably three methods of achieving in focusing manual lenses...
1. Sharpness of the subject in the viewfinder.
2. AF adjustments made to the Pentax AF system
3. As determined by high contrast in the Live view system.
In 1, exact focus will be dependent on placing the camera's focus screen in the correct position. There are various thickness of shims to set this value correctly.
In 2., the camera can be calibrated by setting offsets in the K5 AF Adjustment settings. This will determine when to turn on the green hexagon indicating the lens is focused. In my experience there seems to be quite a bit of hysteresis in rocking the lens barrel for exact focus...
In 3. Focus accuracy as determined by highest contrast on the sensor appears to be the highest probability of getting a sharp image. This method does not depend on a calibrated AF system or focus screen position. The final result should match the exact focus precisely. But this method is slower, and not feasible for fast moving subjects.
After installing a Katz Eye focus screen on my K20d, I found a discrepancy between focus methods 1 and 2. The split image of the Katz Eye clearly shows incorrect focus. The adjusted AF focus point did not match the visible focus point in the viewfinder. I then discovered that the Katz Eye screen was a tiny amount thicker than the Pentax screen, and I had to change the shim in the viewfinder to match. After that proper focus in both methods were identical.
After reading the thread on capture in focus:
https://www.pentaxforums.com/forums/pentax-k-5-forum/170765-catch-focus-accuracy-solved.html
I was also surprised to learn that the AF adjustments that would trigger the shutter when doing capture in focus did not seem to change the focus point. I only tried +/- 5 settings from both directions, but the focus point on my focus chart did not seem to move. I suspect that is probably attributable to the hysteresis I referred to above.
I love my manual focus lenses, and they provide an affordable way to hand held low light photography. I look forward to reading more about the experience of others in achieving sharp focus.
Dick