I too have the Auto Tak 85/f1.8. Short version of the long story, I also have a Contax Zeiss 85/f2.8, that I modified to a K mount (Leitax.com). They are both incredible lenses. My problem - up until now is that I have not shot with them as much as I really should have. I was initially interested in the 85's for some mild telephoto landscapes and a bit of astro. Now, that I am finally retired - I want to go out and start exercising these lenses with visions of Arizona and the sky we have here.
I really need to just get a second M42 K adapter to put on the AT 85 semi-permanently, so that I don't have to dip into the throat of the camera body with my fingers to extract the adapter - at night when I am changing lenses. Otherwise, the lens shoots extremely nice. For nearly a 60 year old lens, it is impressive.