Ok, before I mistakenly posted a pic taken w a Minolta 50 (taken down - thanks Les!), but this time the pic is correct. This was taken w my LX and 40 2.8. I have had nothing but super results with this diminutive lens.
What I was told by the Konica rep in the 60s was Konica 57 1.2 and 1.4 were designed for optimum performance wide open while the 1.7 was best in good lighting stopped down to F8 or 11. If true then I assume the Pentax 1.2 and 1.4 are designed for low light as well. I have the Pentax F2 and 1.7, I have never noticed any difference between the 2 in terms of performance.