Vitaly, I have seen you are using this lens and I wonder how is the focusing ecxperience with this camera. Can you share your experience? Thanks in advance.
Manual focusing experience for me is just fine -- no worries.
Optical viewfinder seems exceptionally bright and clear. Even without "focusing aids" -- such as split image or microprism -- subject focus is generally readily apparent.
As a matter of personal preference, I've been using older manual focus lenses more than half the time. Recently I obtained an m42 adapter to enjoy some vintage screw-mount lenses as well. As the m42 lenses don't provide any stop-down automation on the camera, it means setting the aperture before metering and exposure. When stopped down beyond f/5.6, the viewfinder image does start to get pretty dim and focusing can be more of a challenge.
Recently I was using a 50mm/1.4 Super Takumar, a 7-element version with thorium elements. This lens has become quite yellow-tinted over the years. In the field I did find it noticeably more difficult to focus than the clear-lensed 8-element version, despite the bright f/1.4 maximum aperture. Like the yellow tint was getting in the way of determining sharpness in the viewfinder somehow.
In the end, though, all the images came out fine, very sharp at that thin plane of focus at f/1.4. So it's learnable, or just getting used to it. Though I may yet give this lens a good UV bath if we ever see the sunshine again ;>
Take these comments with a grain of salt. My frame of reference is a bit out of the norm. My basis of comparison includes squinting through Kalart viewfinders on Graflex cameras, and dim fresnel screens on old TLRs. Compared to these experiences, the optical viewfinder on the Pentax is brilliant indeed.