Spad Posted September 18 Share Posted September 18 (edited) .... painting the back of a secondary mirror black on a newtonian?? I have seen a few glootoob vids where they recommend this. Thanks, Ian Edited September 18 by Spad Link to comment Share on other sites More sharing options...
Ratlet Posted September 18 Share Posted September 18 1 hour ago, Spad said: .... painting the back of a secondary mirror black on a newtonian?? I have seen a few glootoob vids where they recommend this. Thanks, Ian I did the sides of mine and did the back whilst I was at it. I did the sides because there was some over spray if the silvering that I didn't want there. I guess really it depends is the answer. I flocked the inside of my tube so it made sense whilst everything was apart to do it. But I wouldn't do it if I wasn't doing the flocking Link to comment Share on other sites More sharing options...
Louis D Posted September 18 Share Posted September 18 I guess it depends on how much stray light you have shining into the back of your tube. I've read imagers really hate stray light making its way in from the back of the tube, ruining their images. You've still got the problem of light coming around the edges of the mirror, though. Link to comment Share on other sites More sharing options...
PeterStudz Posted September 18 Share Posted September 18 (edited) I made a cover (lined with flocking) for my 200p. Some people cover the back of the OTA with a shower cap. If you look down the focuser in daylight I can see obvious stray light getting in when the cover is off. Most of that from around the sides of the primary. For white light solar there’s plenty of light around! I always thought that any unwanted light or reflections that you can see at the focuser will make it to your eyes. Mind, maybe a cover with have an impact on tube currents. Edited September 18 by PeterStudz Link to comment Share on other sites More sharing options...
900SL Posted September 18 Share Posted September 18 I use a 'reverse dew shield' made from yoga mat, with a removable circular stopper. I can collimate and let the Newt cool, then plug it for imaging Link to comment Share on other sites More sharing options...
Spad Posted September 18 Author Share Posted September 18 I have a benny hat i put of the end of the OTA. Was jsut wondering if it's worth taking the secondary out to paint it. I plan to flock it at some point. Link to comment Share on other sites More sharing options...
PeterStudz Posted September 18 Share Posted September 18 I painted the back and sides when I took the secondary out in order to flock. But painting was a 5min job so worth a try. Whether it makes a difference it’s hard to be sure, but it didn’t do any harm! 1 Link to comment Share on other sites More sharing options...
Alan64 Posted September 18 Share Posted September 18 I use a cool, ultra-flat chalkboard-black, from a rattle-can. Link to comment Share on other sites More sharing options...
bosun21 Posted September 18 Share Posted September 18 A black shower cap eliminates any stray light entering around the primary mirror. Regarding the secondary mirror I'm not convinced that blackening the sides has any meaningful effect. If you are flocking the tube and have everything stripped off the scope then I say go ahead and blacken the mirror while it is out. I didn't see any difference by doing it. Shielding the primary I did notice the difference. It all depends on how much stray light you have in the first place. Link to comment Share on other sites More sharing options...
PeterStudz Posted September 18 Share Posted September 18 I used chalkboard-black too… but brushed from a tin. Whatever you decide to use test it on a bit of glass first and make sure it sticks. I initially I tried some of that trendy “blacker than a blackhole, blackest pain ever” and it flaked off as soon as you sneezed - I would t want it anywhere near optics! Link to comment Share on other sites More sharing options...
Damo1965 Posted September 18 Share Posted September 18 1 hour ago, 900SL said: I use a 'reverse dew shield' made from yoga mat, with a removable circular stopper. I can collimate and let the Newt cool, then plug it for imaging I too use a circle cut from a yoga mat with three cutouts for the collimation knobs - fits snugly and blocks everything when looking down the tube in daylight. Link to comment Share on other sites More sharing options...
Peter Drew Posted September 18 Share Posted September 18 If you are using a white full tubed Newtonian it is worth applying externally a patch of flocking opposite the eye not in use. 1 Link to comment Share on other sites More sharing options...
apaulo Posted September 19 Share Posted September 19 Personally i would be very hesitant about putting any paint inside my scope. Paint will and does break down and flake in all sizes of particles. The bits can only fall in 1 direction and thats onto the primary mirror, which isnt a great thing to happen. Paul. Link to comment Share on other sites More sharing options...
Alan64 Posted September 21 Share Posted September 21 The paint I use is solvent-based... It does not shed, or flake off. It's fine as long as it isn't touched... The so-called "blacker than black" paint is water-based, an acrylic, and may shed, especially if touched... https://www.culturehustleusa.com/products/black-4-0 Whatever is used, research for reports of flaking or shedding. I always flock the tubes of my Newtonians, and it doesn't shed or other. All of my telescopes were blackened with paint to varying degrees at the factory, and I haven't seen any detriment as described. 1 Link to comment Share on other sites More sharing options...
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