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Stargazing Protecting Optics (not eyes) During Solar Observing

  1. Aug 18, 2017 #1
    Hi, I dont have much experience with amateur astronomy, but I was going to try and take a few shots with my Canon EOS 20d mounted on my 6" Ritchey-Chretien astrograph this Monday. The telescope was manufactured by Orion, and was a few hundred dollars so probably not the highest quality. Since I'm a teacher, I'm planning to have it setup for most of the occultation's 3 hours for students to check out.

    My concern is heat. Should I worry about adhesives on the optics? What about the CCD in my DSLR? I'm really in the dark about solar observing with a telescope. I do not want to damage my scope.

    My only filter is a single layer of mylar.

    edit: Extra question, I will have to unmount my telrad because that specifically had a warning against solar observing. Recommendations for a simple replacement for easy centering? Its just an alt/az mount without tracking or autoguiding, etc.
     
  2. jcsd
  3. Aug 18, 2017 #2

    fresh_42

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    You should be more concerned about your eyes. These cannot be replaced, optics can. It's really dangerous. Why don't you ask the company you got your telescope from about special filters for this event? Maybe an IR filter to protect the telescope from overheating and UV filters to protect your eyes.
     
  4. Aug 18, 2017 #3
    I'm not planning to use an eyepiece at all, just the DSLR. I received a pair of eclipse goggles from the AAPT because of my subscription to the American Physics Journal, so not worried there. Also the school bought goggles for the entire student body.

    edit: but yes, its a little too late for manufactured solutions from the telescope supplier. Is the IR that damaging? Thats dissapointing if so.
     
  5. Aug 18, 2017 #4

    davenn

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    nowhere near enough <--- I cant stress that enough

    you need to stop down the aperture from 6" to around 2" using a cover plate over the front of the scope with that 2" hole in it

    THEN ... over that 2" hole use at least 2 to 3 layers of mylar

    Dave
     
  6. Aug 18, 2017 #5
    That can certainly be done. But what exactly is the hazard? I'm just trying to understand. What does solar observing do to a telescope with a DSLR on it? Should I make efforts to cover the primary every instant its not in use? Like I said it will be sitting out there for a good 3 hours.
     
  7. Aug 18, 2017 #6

    davenn

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    burn the crap out of the optics and insides of the scope
     
  8. Aug 18, 2017 #7

    davenn

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    if it's not pointing at the sun it doesn't matter
    but safer to keep it covered to save a moment of non-thinking carelessness and pointing at the sun without protection
     
  9. Aug 18, 2017 #8
    Sorry, I don't mean to sound like an idiot, but what do you mean? The reflective lining on the primary will get so hot a hole shall be scorched in it, or what? The CCD's noise will go to infinity?
     
  10. Aug 18, 2017 #9

    davenn

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    do you not understand what the word burn means ? :wink:

    enuf heat to crack glass optics and burn/melt any plastic parts etc etc
     
  11. Aug 18, 2017 #10
    Wow, alright, well...that was what I was fearing I guess.
     
  12. Aug 19, 2017 #11

    rbelli1

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    And then proceed to crack/melt/burn the inside of the camera.

    Forcing the magic blue smoke out with external means is just as damaging as letting it out though internal means.

    BoB
     
  13. Aug 19, 2017 #12
    Wait, I've seen some transit setups without any filters at all where projection was used. Can that only be done with pure refractors?
     
  14. Aug 19, 2017 #13
    solar-filter-telescope.jpg

    I think I could do something like that fairly easily. Looking at my secondary, there is only about 1.5 in clearance, and the only dill bit for circular holes I have on hand is a 15/16".

    So, I'd be stopping the aperture down to 15/16", with 3 layers of mylar. Is that enough? Should I throw a layer of glass or polycarbonate in there as well? I think the only plastic parts in my scope are the baffle down the main tube. But I'm not sure about the adhesives and as mentioned the IR effects on the mirror/CMOS sensor is pretty scary.

    My field of view is .94 x .62 degrees. Probably the longest time pointing directly at Sun would be during focusing.
     
  15. Aug 19, 2017 #14
    If that is your 6 incher there I would humbly suggest that the hole is too big. I have a factory cover for my 5 inch with a smaller hole and it is just enough to make a bright moon comfortable to look at. Just a suggestion; Why not make some smaller holes in pasteboard for example and tape them over the hole that you have. Start small and work up carefully. Of course you need to use a very dark filter over the hole as mentioned above. I am using two lenses from old fashioned welding goggles.
     
  16. Aug 19, 2017 #15
    That pic is not my telescope, but that off-axis solar filter is what I'm trying to make. I think I will drill 15/16 inch hole then cover with various pasteboard holes a bit smaller as you say, thanks for the tip.
     
  17. Aug 19, 2017 #16

    fresh_42

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  18. Aug 20, 2017 #17
    Thanks, fresh.

    I've got my aperture stop all constructed with a 15/16" hole. I'm starting to think the best idea would be to just cut my eclipse goggles in half and use that. Each eye has a 1.5" by 1.5" of the material.
     
  19. Aug 20, 2017 #18
    Think I've got something that will work. Here's a few quick shots and a horribly off-center showing color for Sun.

    DSCF3396.jpg
    IMG_8196.jpg
    DSCF3397.jpg
    DSCF3398.jpg

    Just need to rig up a good aiming solution and think I'll be set. :)
     
  20. Aug 20, 2017 #19
    Found a great solution to targeting! I just put the other cut eclipse goggles eyepiece on my Telrad's glass plate. Check this out:

    DSCF34001.jpg
    [​IMG]

    First pic is outside, you can see the Telrad reticle with actual Sun orange spot far off to the top left.
     
  21. Aug 21, 2017 #20

    davenn

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