The advantages of a ball scope are obvious,
but probably the reason so few are built is the difficulty of finding a sphere.
This was the discussion David Davis and I were having while waiting for trout to bite.
David was reminded of a conversation he had with another friend, Tom Conlin.
Tom had designed a mount for David using intersecting circles to define a sphere.
I was dubious that such an approach would work, but I was intrigued by the idea.
After arriving home I constructed a small model. I used three half circles of Plexiglass set at 120 degrees to each other and set it in a ring.