I have been watching the progression of this topic over the last week and wonder why no one has suggested black felt. I have covered the inside of my 10" f4 (classical cassegrain) tube with it and found the stuff easy to work with and very dark. You have to make sure you have the nap in the proper direction, but after that, it is just a matter of smothering the inside of the tube with contact cement and you are off to the races. Don't forget the inside of the bottom of your focuser as well. Makes me wonder why most of them are shiny. Even black anodized aluminum is very shiny at such steep angles.
Just a thought.
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