This is the Pentax Takumar 50mm f1.4 lens in the 8-element version with an m42 screw mount.
This unusual lens has good center sharpness even at 1.4. Cosmetic and mechanical condition is very good, as is shown. No scratches, no dust, everything works smoothly and as it should.
There is a small amount of "balsam" visible at the far outer edges of one of the interior elements, but I think it may be outside the light path. In extensive use and testing I cannot see any effect of it. I have owned the lens several years and there has been no change in the balsam.
The 8-element version was made for a short while by Asahi before they settled on a less costly 7 element version. It is generally regarded as among the sharpest of the 50mm 1.4 lenses made. It can be identified by the protruding rear glass element and the location of the infrared mark.
I have posted some test photos that highlight center sharpness (I have used it as a portrait lens on APS-C A6000). You can download them from here if you wish https://www.flickr.com/photos/60134436@N03/shares/W5W6YD
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