ProOptic Maksutov Cassegrain 500mm f/5.6 mirror telescope lens

introduction

this super telephoto lens is a Maksutov Cassegrain catadioptric mirror lens, and as with all such mirror lenses, share the following characteristics:
- manual focus
- fixed aperture (in this case f/5.6)
- 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
this lens is designed as a telescope having a T2 screw mount to attach to cameras, but also a thumb screw to lock in eyepieces.
unlike photographic mirror lenses, it has a manual focus knob rather than the barrel acting as a manual focus control

500mm focal length and field of view (5°) at infinity focus
fixed f/5.6 aperture
closest focus 1.5m although this will require many rotations of the focus knob
filter thread ?95mm
no built-in sun-shade / lens hood
105mm diameter, 220mm long and 1220g
a 105mm solar filter can be slid over the end for photographing the solar eclipse photography