I love to shoot with manual lenses and noticed that my K-5 was a bit off in that department, which led me to read up on the subject. First of all, many thanks to all the previous posters and especially those,
that have provided pertinent information on acquiring the little bits and pieces from Pentax.
Once again, the link for the parts:
https://www.pentaxforums.com/forums/pentax-k-5-forum/131473-k-5-manual-focus.html#post1367571
Anyway, once the washers arrived, I decided to first test seven different manual lenses (all wide open) with the factory installed "focus adjustment washer",
just to rule out sample variation of my SMC-M 50mm/1.7 & SMC-M 100mm/2.8, with which I had initially tested manual focus accuracy. I did this on a tripod with shake reduction off and the 2 second timer on.
Diopter adjustment was the same for all shots. All lenses exhibited about the same amount of front focus.
In a previous test I had tested the 50mm and 100mm lenses with the factory installed washer removed, resulting in back focus of about the same margin as front focus.
I had ordered 0.1, 0.15, 0.2, .25 and .3 washers and decided to install the .2 washer, which more or less hit the sweet spot. I may yet try the .15 washer at some later date, to bias the focus a little further to the back.
Here are some images that may help explain it all:
I created the pattern with Excel and turned the LCD display by ~45 degrees.
Through the viewfinder, the green square was in focus to my eyes.
After changing the washer. This shot is not entirely representative of all results; there is a small margin of focusing error in this one, but it's good enough to convey my point.
Some tools I used and a loose washers..., shot after adjustment.
And hopefully a clear shot of the retaining latches and the position of the "focus adjustment washer". The focusing screen has already dropped and is out of view. This is the mirror box from my K-7, which is more or less identical to the K-5.
I spent the rest of the available daylight taking some "wide open" shots in the real world. But even with accurate/improved focus it can still be a challenge to get it right, but for now I'm satisfied.
I rarely shoot wide open. Lets say I'm more inclined to do it more often. Practice, practice and practice...
K-5, SMC-M 100mm/F2.8, 1/800sec @F2.8, ISO 100