I have been using these Pentax 67 lenses for a little while now.
The 55mm F4 is OK but needs to be stopped down a bit and run at 2x2 binning to get rid of aberrations but is nicely very widefield. The 165mm F2.8 though runs fully open with little to no aberrations except a bit of chromatic aberration.
It lacks the resolution of a telescope but still fun. Bright stars come out a bit magenta and that needs to be processed out but otherwise it shows up a nice area reasonably well.
I took this one a while ago. I don't think I've nailed the processing yet but it didn't turn out too bad.
3 hours 15 minutes. 5 minute subexposures, F2.8, 2x2 binned, LRGB:
http://www.pbase.com/gregbradley/image/138661800/large
Greg.