Ok, I am stepping out of the bargain bin for the moment.
I bought an ISCO Cinelux-Ultra 65mm f/2 for $80 shipped from the small town of Crockett, Texas, where the lens used to project movies at the Ritz Theater there. For size comparison, I have it here with the ubiquitous Helios-44 58/2 and the miraculous Pentax FA 77/1.8 Limited. You can see it is quite a bit bigger... until you remove the fanciest, sturdiest lens hood I have ever seen. The actual optics are amazingly small.
This lens was Schneider's first use of the Cinelux name they acquired from Kollmorgen in 1973, manufactured by their ISCO division in Göttingen beginning in the late '70's. In tribute to the original brass Cineluxes of the '50's, these new aluminum lenses were made with an anodized gold finish. They were an updated version of ISCO's Super Kiptar, with 6 elements in 6 groups (they did not want to use any cemented doublets because of the extreme heat projector lenses can experience). This optical diagram is from a fascinating article written by one of the designers, Karl Macher, available
here, which describes many of the technical aspects of projection lens design.
This new series of lenses was so much better than what had come before that the designers were presented with an Acadamy Award for Outstanding Technical Achievement. Unfortunately, the rest of Schneider's business was not doing so well, and the company filed for bankruptcy in 1983. They were able to restructure and continue as a business, but ISCO was spun off into its own company, and became a competitor. Schneider retained the "Cinelux" trademark, so the fact that my lens says both "ISCO" and "Cinelux" means it was made before 1983.
Anyway... that's the history. Here and now, I really love this lens! It is incredibly sharp and full of contrast. Subjects seem to jump right out of the frame.
The colors are wonderful, and bokeh is way better than it should be for a lens design which did not consider out-of-focus rendering at all.
The image does smear a bit in the extreme corners. Because of the orientation of the film (vertical for movies, horizontal for stills), 35mm movie frames are about the same size as an APS-C sensor. The fact that this lens covers a full-frame sensor is a happy accident, and I have since learned that I got extra lucky here: the 65mm lens is about the lower limit on full-frame coverage. Black corners start to appear on the 60mm lens (they were offered in 5mm increments to cover different theater sizes). Longer focal lengths have progressively larger image circles. Later in the '80's, other versions were made to cover 70mm film as it briefly came back into vogue, but they are uncommon and expensive now.
The distance between the back of this lens and the sensor is 39mm. I checked and it does not hit anything on a K-5. I don't know if the same is true of a K-1 or other full-frame SLR's. Longer focal lengths get progressively longer back-focus distances. Lenses of this series 70mm and longer should be safe for any DSLR.