Arri S16/SR2 Lens

Zeiss Tessar 12cm f2.7 VI2 (48mm/O, close focus abt 4ft, 630deg helicoid).
c1924 s/n 600379. (with T2 to Nikon or PL adapter).
A Jena Zeiss, prewar... brass and chrome barrel design untypical of 1940/50s M42 Jena lenses.
Tessars are reasonably sharp, but not fast lenses. An early design, and this one of peculiar provenance and medium format may not be typical anyway.
Edmund Hillary used a Korelle/Zeiss combination on his Everest expeditions!.

It's a little soft at f2.7. Looks sharp across ½frame @ f4.

Out-of-focus areas are usually very soft, though sometimes a light halo. Always circular as the aperture is a 16 bladed perfect circle at all apertures. Covers full frame without vignetting (originally a medium format lens).

12cm on 50D

f2.7