My dad's old SMC Takumar 50mm f1.4, late model with rubber ring, getting some new life with my new K-01. I had to de-yellow this lens a few months ago. I let it sit up against a black-light, the fluorescent type, for about 8 days. That cleared it up all the way.
I own the Pentax-M 50mm f1.4, the M f1.7, and the Pentax-A f1.7. There is clearly something to the aura or quality of the images with the Tak. Maybe it's the radioactive glass, I don't know, but the bokeh is magical, and the 3D factor is immense. It's a special 50 for sure...
Here are a few shots with the SMC Tak 50...
The close-up of the green door is a crop of the bigger view to show the killer detail this lens has.