|
My first guess is you have a refracting element in the path which has at least one or both sides that are not AR coated, and is not perfectly perpendicular to the optical axis - what you are seeing is multiple reflections off that. The stray reflections are also slightly out of focus meaning there must be a path length difference involved with respect to the primary image.
To my eye the reflections suggest that if there is a clear glass element somewhere in the path and the surfaces are not exactly optically flat and plane-parallel - a few fringes of wedge will produce what you're seeing if the surfaces are not anti-reflection coated.
You mention a filter, let me guess - your OTA sealed with a clear glass UV filter ?
|