Sigma 500mm f8 Mirror Ultra-Telephoto - Lens

T2 is a standard screw thread mount for cameras and other optical instruments f.ex telescopes and microscopes. T2 mount (42 mm diameter, 0.75 mm thread pitch) should not be confused with the M42 mount (42 mm diameter, 1 mm thread pitch). Flange focal distance of the T2 mount is 55mm so it is adaptable to most 35mm systems.