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I was watching this (rather old) episode of The Making, where they show how a telescope is built in a factory. At 7:34, the cylindrical body of the telescope is shown to have a dark coating on the inside and the video explains that this prevents internal reflection of the light received from whatever you're observing.

I saw an interesting comment from Izumikawa Fukumi who asked if the telescope would become more accurate if they coated the inside with the blackest black in the world. How would such a dark coating affect the telescope's performance?

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  • $\begingroup$ Cross-posted to physics.stackexchange.com/q/560572/123208 $\endgroup$ – PM 2Ring Jun 20 '20 at 13:10
  • $\begingroup$ Sorry, this site can be a little slow, especially on weekends. But we prefer that people don't cross-post questions to other sites on the Stack Exchange network. $\endgroup$ – PM 2Ring Jun 20 '20 at 13:12
  • $\begingroup$ Ah, my bad, I didn't know if this was the appropriate place to post it so I figured I could try the more general physics SE. $\endgroup$ – JansthcirlU Jun 20 '20 at 13:16
  • $\begingroup$ No worries. Most of the Astronomy regulars also look at the Physics site, but not vice versa. We accept most questions relating to telescope construction here. On Physics, they'd generally get closed for being an engineering question, unless they ask about core physics principles (like this one does). $\endgroup$ – PM 2Ring Jun 20 '20 at 13:23
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Telescopes have the inner part of the tube blackened to minimize scattered light reaching the eyepiece. Such scattered light reduces contrast, and hence reduces the ability to see very faint objects, or low contrast detail. A complementary approach for refractor telescopes is to use baffles in the tube. The baffles form a physical barrier to scattered light. However baffles are costly to make accurately and add to the weight of the telescope.

The more that scattered light is reduced, the better the performance.

Alternatives to super absorbing paint are to attach to the tube, either matt black velvet, or sand paper sprayed with matt black paint.

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  • $\begingroup$ Amazing! Are there any comparisons of telescopic images of the same object which have different levels of contrast? I find it hard to picture. $\endgroup$ – JansthcirlU Jun 20 '20 at 19:52
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    $\begingroup$ @JansthcirlU - I don't know. What you would need is before and after photos using the same telescope, on the same object, under similar skies. That's asking for quite a lot. $\endgroup$ – Dr Chuck Jun 20 '20 at 20:16

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