auto mamiya/sekor 55mm F1.2

   i just got this lens,.

auto mamiya/sekor 55mm F1.2

              This is Auto Mamiya/Sekor 55mm F1.2, has a m42 screw mount, six aperture blade, weighs heavier than my Nikkor-s auto 55/1.2 maybe around 500gr, with 0.5m minimum focus distance and takes 55mm filter size.

auto mamiya/sekor 55mm F1.2

auto mamiya/sekor 55mm F1.2

            The lens slightly has a yellowish tint to the glass, probably due to contain radioactive thorium oxide such as those in mamiya/sekor 55mm F1.4 (pre-SX version). the use of thorium oxide intended to produce glass with high refractivity and low dispersion, this allows lens designers to minimize chromatic aberration and utilize lenses of lower curvature. the radioactivity of the thorium caused the glass turning yellow or brown over time.

           I took some sample pictures with Nikon D60, since I used a regular M42-nikon adapter so infinity focus can't be obtained. all pictures are straight out of camera JPEGs taken on its largest aperture(F/1.2), just resize.

                Im googling to find information about this lens, but I did not find any about this lens on the internet. someone in a manual lens forum said that he has a mamiya/sekor lens chart from the 60s and this lens is not in the list. guess maybe it's a prototype lens? I dont know for sure, but the serial number shows No. 41001. This could be the first of a very few lenses are made for internal evaluation and never in production. 

if that so then I was lucky to get a very rare non-production lens.