Canon FD 35mm f/2 breech mount, concave front element version, pre-S.S.C. with chrome snout
Canon EF with mirror and diaphragm prefire

Vignetting = C @ f/2, B @ f/2.8, A- @ f/4, A thereafter
Distortion = barrel

Aperture Center Corner
f/2      A-     B
f/2.8    A      B+
f/4      A      A
f/5.6    A+     A+
f/8      A      A+
f/11     A      A+
f/16     A      A

Note:
Incorporates radioactive, thorium floride ("rare earth") glass
which imparts a warm green tinge to the pictures.
Best use as an exceptional quality lens for black and white photography,since it doesn't match the color of other Canon FD lenses and will color cast color slides.
Very high contrast at all but f/5.6 and f/8 where it is extremely high.
Optimum aperture f/5.6.