I have a Contour action camera that I sometimes use on a suction cup mount on glass to record something out a window. (Say, the scenery outside a moving train.) To block reflections on the window glass from light inside, I'm going to make some sort of large ring that slides onto the end of the camera. I think I've seen these available commercially before. What are they called?
Here's a mockup... black is a piece of rubber or plastic that I plan to make to put on the camera. The blue is the window.
I'm not sure what you would call this... it's not really a baffle. But, what is it?