see also:

• super telephoto mirror lenses

• this super telephoto lens introduced in ? is a catadioptric mirror lens, and as with all such mirror lenses, share the following characteristics:
  • manual focus
  • fixed aperture (in this case f/4)
  • virtual elimination of chromatic aberration as uses mirror rather than lenses
    • also means focus position for infrared photography is the same as for light photography
  • central mirror:
    • allows much more compact lens length as the optic path is reflected internally twice
    • by necessity, blocks some of the light and thus causes:
      • decrease in image contrast
      • characteristic “doughnut” shaped bokeh imagery in out of focus areas

• 500mm focal length and field of view (5°) at infinity focus
• fixed f/4 aperture
• lens elements, ? groups
• closest focus 15m (3m via an extension tube)
• rear filter thread
• T lens mount thread
• 159mm diameter, 216mm long and 2.7kg (6lb)
• comes with a special lens cap that has a removable inner section. Leaving the lens cap in place, but removing the inner section, cuts the mirror's aperture to f/5.6
• matching 2X teleconverter