rmalarz wrote:
My suspicion is that it's the iris blades of the lens. The light is hitting them and reflecting back to the inner surface of the filter. Then, reflecting off that surface and going into the camera.
Are you shooting directly into a light source?
--Bob
Bob is correct. One reason it is happening is because of the space between the front of the lens to the filter. 3 step up rings is a lot of space.