The edges of a portrait or scene become gradually darkened or washed-out, enhancing the composition with a tunnel-vision effect. The adapter body is machined from black Delrin; the narrow barrel is machined from aluminum with flat black paint inside. This is my adapter for a Global (brand) operating (surgical or dental) microscope, with attaches a LoupeCam miniature HD camera to the microscope beamsplitter.
The term kinematic in this context means that the mechanism provides minimal mechanical constraints to locate the components relative to each other. The threaded end on the left attaches to the digital camera. You can also read the original Topcon TRC-NW3 instruction manual [6 MB PDF file, 31 pages]. Topcon TRC-50VT Retinal Camera This adapter kit converts a Topcon TRC-50VT retinal camera (also known as a fundus camera) from the original film camera back to use a Canon EOS digital SLR camera. Here is the adapter and beamsplitter assembled with a Canon 40D digital SLR camera. A screw-and-lockring feature on the adapter allows for parfocal calibration of the camera to the binocular eyepiece view of the Zeiss instrument. The film camera also provided a reflex viewfinder. To adapt this instrument for digital photography, we first remove the film camera and replace it with a custom-machined threaded bushing that fits around the exit lens and is attached with screws in place of those that held the rails. However, see my custom adaptation of the SD750 and SD790 above.
More photos for this Zeiss project are here. Here are some more digital camera microscope adapters I made for a customer. The endoscope provides a standard mushroom-shaped end («B-cup») to the eyepiece. The original compact camera body used 35mm film in direct projection and was attached with a locking rail mechanism.