Hi! I just picked up a yellow brick from Adorama, and decided to do some tests with old school filters.
I started with the K-01 on a tripod and an old PENTAX-A 50mm F1.7 lens. I set the camera to manual, to ISO 100, and to F7.1 for a little sharpness.
Then I put an old school linear polarizing filter on it. Here are two shots at different filter rotations:
The one on the left was at 1/10 and the one on the right at 1/8, very close in exposure. You can see through the dirty glass better, and some of the leaves have more color due to no sunlight reflection. I hope this means that it is ok to use this filter on this camera.
Then I went crazy and tried an R72 Infrared filter:
The one on the left is at ISO 100 and a 30 second exposure, the one on the right at ISO 3200, f1.7 and 1/20. Lots more noise on the right but almost handholdable. Having live view made the focus shift trivial.
I used
Raw Therapee Portable for processing, and copied the processing settings to ensure similar croping and such. I fiddled with channels to get the IR shots from bright red to this, and didnt work very hard on the second one.
Overall I'm very pleased with the camera, I'm able to use my old lenses and filters and get very nice results.