This is an optical mount which allows the coupling of a Nikon F-mount lens to a C-mount lens. The spacing between the mounts matches the combined flange length of the F and C mount lenses, so that the focal point of each lens is in the same plane. As a result, with both lenses focused on infinity, connecting two lenses with different focal lengths with this coupler is a simple way to create a telescope or laser beam expander.

The model includes multiple holes suitable for attaching M6 threaded screws, and 4 foles on the F-mount side allow the insertion of alignment rods (e.g. Thorlabs cage rods) to simplify alignment of multiple telescopes. The F mount side includes a notch for the aperture lever for Nikon lenses without an aperture ring. 

The attached photographs show the coupler with a 12mm Edmund Otpics lens attached to a 50mm Nikon AF-S 1.8G lens.