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Message: <blockquote data-quote="Paul Corfield" data-source="post: 1425181" data-attributes="member: 19132">I use the tube that came with the GSO barlow as a 50mm extension tube but the inside of that is shiny also. Like you I just pull in and out to adjust focal length. Yesterday I lined the whole thing from front to back with black material but it had no effect on internal reflections. I think the barlow glass element itself is the main source. Must be something to do with the way light passes through them or the multi coatings need to be better to improve light scatter, probably a combination of both. I read somewhere that the Dakin barlow only has a single antireflection coating rather than a multicoating and this is to reduce what they call "narrow angle light scatter". Apparently multicoatings produce more light scatter than a single layer coatings.Some barlows have a baffle halfway down the chrome barrel which would put it behind the glass element. I tried this by putting one inside the T-mount and it has an effect on contrast but not to the same level as putting one in front of the element.Paul.</blockquote>