Pentax 50mm f/1.4 Super Takumar (radioactive, screw thread)
Pentax Spotmatic SP 1000 with manual (stopped down) diaphragm and cable release
Vignetting = B- @ f/1.4, B+ @ f/2, A- @ f/2.8, A thereafter
Distortion = pronounced barrel
Aperture Center Corner
f/1.4    C+     C-
f/2      B      C
f/2.8    B+     B+
f/4      A-     B+
f/5.6    B+     A-
f/8      A-     A
f/11     B+     A
f/16     B      B
Notes: Discolored (yellow) glass due to one or more radioactive elements. Moderate contrast at f/1.4 and f/2; moderately high contrast at f/2.8 to f/5.6; high contrast at f/8 to f/16.