Sometimes when I am binoviewing with my William Optics binoviewers, I notice "ghosting" of a star, (or something else), while viewing.
It's kind of hard to explain. It doesn't have to be bright stars or anything "bright" I am looking at, but this strange light source will drift a different way than stars do when using my 10" Orion XTi, without tracking.
I tried changing eyepieces in the binoviewer, and even switching eyepieces from side to side, but it still happens from time to time.
I am thinking it is something to do with the prisms.