So I got the focusing screen in yesterday. Here's my limited review and some tips for anyone else who wants to switch out the stock screen with one from focusingscreen.com:
First off, the focusing screen works great! This is the most important thing to come away with. I'm able to nail focus with the Pentax-A f/1.2 pretty easily, even in very low light (EV=8 here):
https://i.imgur.com/GQIXG23.jpg
I have not had issues with blackout on the split-prism, though the narrowest aperture lens I've used with it so far is f/4. Still, the split prism is more than usable at this aperture.
The downsides:
I had a heck of a time getting the thing installed. I'd put aside a few hours uninterrupted for getting the new screen installed and the focus set correctly. The new screen came with three plastic shims for getting the focus dialed in, one thick shim and two thin shims. Initially when I installed the screen I was getting front focusing from the lens. In order to resolve that, I had to remove the factory-installed metal shim from my KP, and replace it with the two thin shims from focusingscreen.com. It took a while playing around with a tripod and a focus chart (I used the chart from here:
Squit Photo) to get the shim combination correct so it wasn't front or back focusing. Use a sturdy tripod and don't put it on carpet. I kept the old shim in case I ever decide to reinstall the factory focus screen. Here's the final result with the two thin shims stacked on top of each other:
https://i.imgur.com/EUDitLh.jpg
---------- Post added 11-25-20 at 09:42 AM ----------
Oops, I forgot to include pictures of the actual screen from the viewfinder. Here's a white, diffuse background so you can see what it looks like:
https://i.imgur.com/8Cw8SIS.jpg
Here's an in focus picture of my desk-toy:
https://i.imgur.com/szrkdke.jpg
Here's an out of focus picture of the same desk-toy:
https://i.imgur.com/mwGnKgu.jpg
I'm going to go in later and clean up the dust I accidentally got in there. Now that I know what I'm doing I think it'll just be a few minutes and the rocket air blower to get it nice and clean!