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/)
  • 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

• 400-600mm focal length and field of view (2.5°) at infinity focus
• fixed f/8-12 aperture (varies with zooming)
• 12 lens elements, 7 groups
• closest focus 3m (0.4x macro)
• 67mm front filter
• 40.5mm rear filter thread
• Pentax K lens mount
• 82mm diameter, 108mm long and 730g