this super telephoto lens was 1st introduced in 1965 and is a catadioptric mirror lens, and as with all such mirror lenses, share the following characteristics:
manual focus
fixed aperture (in this case f/11)
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
NB. the 1st Nikkor mirror lens was designed for rangefinder cameras in 1959 and was a 100cm (1000mm) f/6.3 which had close focus of 30m and weighed 10kg!
the 1st version of a 1000mm f/11 was in 1965, had 5 elements in 5 groups and close focus to 8m
a new design was introduced in 1974 allowing for screw on rear filters instead of a turret design
the last version was introduced in 1976 and included NIC coating and improved handling
Nikon stopped making mirror lenses in 2005
specs
1000mm focal length and field of view (2.5°) at infinity focus