After all these years, I just now noticed that the finder is one of those ubiquitous elbow scopes that were used in military equipment. But, how the heck do you use it?!
My 1967 home-made 8-inch f/4.8 reflector still has that old war surplus M17 elbow telescope. That elbow scope had previously been used as a finder on my home-made 6-inch f/7 Newtonian. I believe these were used as gun sights for a tank cannon. And that stands to reason since they are MIL-spec - "built like a tank". Edmund used to sell these with either coated or uncoated optics. Mine was uncoated, due to the challenged finances of a teenage student.
As for how to use them, the technique was to sight along the inside right-angle edge, below the filter carousel. With some care and practice it was possible to point the telescope close enough for the intended target to be within the FOV of that 8X50 scope. This was, of course well before the go-to revolution. For 45 years (from 1963 until 2008) it had been sky atlas, finder scope, and star hopping to the intended target. Now with my Losmandy G-11 (Gemini go-to), I don't miss the low tech, manual method. At 72 years of age my old back appreciates the ease. Now it is hard enough bending over to center 3+ stars in the Telrad on my SCT scopes, for go-to alignment.
But if the battery goes dead or the electronics go up in smoke, I can still find my target the old way.