Arri S16/SR2 Lens

Zeiss Tessar 8cm f2.8 (37mm/O, close focus 3' 6", 270deg helicoid).
c1937 s/n 2104523. (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. The Zeiss 2.8 tessar was the most expensive lens option on medium format cameras in 1940 ($25 more than a Schnider f2.9 or $32 more than a Steinheil Cassar f3.5 -ref Sears catalogue).
Edmund Hillary used a Korelle/Zeiss combination on his Everest expeditions!.

It's very soft at f2.8. Looks sharp across ½frame @ f8.
Highlights have a strong white corona. Originally uncoated, it now has a soft blue oxidation.
Out-of-focus areas are usually very soft, though sometimes a light halo. Always circular as the aperture is a 15 bladed perfect circle at all apertures. Covers full frame without vignetting (originally a medium format lens).

8cm on SR2