This is a boresite for focusing fastair cameras. It is a standin for the camera wherever the camera may be positioned and need to be focuses.
The front bit of the black optical tube has a lens with a crosshair etched in the flat surface there. The opposite end is an eyepiece thru which you can focus and view the eyepiece. There is a two piece draw tube focuser which is secured by the two set thumb screws on the right side.
It is all in a a nice Wollensak wood case for storage.