this super telephoto lens is a catadioptric mirror lens, and as with all such mirror lenses, share the following characteristics:
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
originally designed by Minolta in 1991 and re-introduced by Sony in 2006
specs
500mm focal length and field of view (5°) at infinity focus (but gradually changes to 320mm when closer focus at 4m - this may be an issue with cameras where you need to set a focal length for the image stabiliser to work optimally)
fixed f/8.0 aperture
5 groups / 7 elements
closest focus 4m which gives 19cm x 28cm (7.5“ x 11.0”) field of image
82mm front filter thread
rear section filter holder, drop-in type (with 42mm filter)
built-in sun-shade / lens hood
89mm diameter, 118mm long and 665g (compare this with 255mm and 1.3kg for a 400mm refractor style lens)