Originally posted by aleonx3 Shims are the metal 'spacers' that usually comes with third party focusing screens; it is to be used to correct the distance from the mirror. Before you do anything else, you want to make sure that it is not focusing screen problem. When you say the focus seems to lock on when you look through the viewfinder, but the actually picture turns out to be blurry. When you say lock-on, do you see the green hexagon comes up in the viewfinder? The green hexagon comes up means the camera's PDAF system is seeing the focus to be correct. If the green hexagon does not come up, it does not mean it is in focus by the camera system. I just want to make sure that you don't get mixed up with the diopter on the camera.
I am pretty sure it is not the camera, I have 3 ways to check it, one is that when I place my old focusing screen back and attempt to focus, I manage to get in focus shots, even with the dirty, spotty and scratched focusing screen.
Then I checked it with focus peaking via live view and the picture is razor sharp. Except that the new focusing screen shows the picture completely out of focus while live view and focus peaking shows perfect focus of the object.
then there are the red squares that indicates focus point. it is centered and I believe with manual lenses only centered focus works to indicate whether it is in focus. again, if I trust my eyes and new focusing screen, picture is out of focus when it shows perfect focus, then if I play around and hit the spot when the red square lights up and take a shot, it is in perfect focus, but what i see via view finder is not in focus at all.
The focusing screen I bought is Pentax manufactured. Apart few Sigma lenses, there are no other third party products for pentax in my country, we have only few specialized shops that sell anything Pentax. ( I dind;t take into count filters for lenses)
I guess there is no other DSLR brand with which the one could get such rich learning experience about DSLRs in general.