this super telephoto lens is a catadioptric mirror lens, and as with all such mirror lenses, share the following characteristics:
manual focus
fixed aperture (in this case f/8.0)
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
original version was produced in 1968 and replaced the large Nikon 500mm f/5.0 mirror lens (only 2,500 made) and dramatically improved close focus from 48' to 13'
revised “C” version with improved lens coating introduced in 1974 and Nikon made ~70,000
a new design “N” version “Reflex-Nikkor” was introduced in 1984, Nikon made ~30,000, and it has an orange line that runs around the focus ring
the older the version of this lens, the softer the image will be
Nikon stopped making mirror lenses in 2005
specs
500mm focal length and field of view (5°) at infinity focus
fixed f/8.0 aperture
6 elements in 6 groups (5 elements in 3 groups for “C” version)
NIC coating
closest focus 1.5m (4m for “C” version)
82mm front filter thread rotates with focus (88mm for “C” version)
rear 39mm screw in filter
screw-in sun-shade / lens hood
89mm diam x 116mm long and 823g (93mm diameter, 142mm long and 1kg for “C” version“)