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Thread: The "Sun funnel"

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    Default The "Sun funnel"



    With the solar eclipse coming later this year, I thought I would reserrect this thread from a few years ago.

    Build a Sun Funnel

    When I first saw it I was skeptical about the amount of heat that would be generated. After some assurances by the OP, I decided to give it a try. Using the materials recommended in the original article, it works great! I have used mine a number of times to view sun spots, the Venus transit a few years back and a partial eclipse. It works especially well for daytime out reach events!

    Heres a link to the full instructions.

    https://www.astrosociety.org/tov/Bui...un_Funnel2.pdf
    Gordon
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    Default Re: The "Sun funnel"

    Great idea! I will have to give this one a try. When doing daytime outreach at schools, this would be a great way to let several students see the Sun at once.
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    Default Re: The "Sun funnel"

    Member terrynak uses this method for outreach frequently. Pretty darn cool!
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    Default Re: The "Sun funnel"

    I have a Vixen 70mm refractor on a EQ5pro mount that I piggy back my LS35ta Lunt solar scope on when I do daytime outreach. It works great! A group can view solar spots, while one person views via the solar scope! It helps keep everyone involved.
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    Default Re: The "Sun funnel"

    Here is a more current link for the rear projection stuff.

    Da-Lite High Contrast Da-Tex (Rear) - 95774
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    Default Re: The "Sun funnel"

    This very neat! I would be a little skeptical myself, but from the looks of it (and hearing of others use) it is perfectly safe. What a great way to do some basic solar observing for multiple people at once.
    It's also a great excuse for us reflector only owners to have a refractor lying around (I wonder if my wife will buy that one)
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    Default Re: The "Sun funnel"

    Something I am confused about. There is no filter on the objective end? Wont you cook the eyepiece?
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    Default The "Sun funnel"

    That's one reason why they use a cheap simple eyepiece . Also, the focal plane will be some distance away from the eyepiece when focused (more than the focal length of the eyepiece, but less than twice that, measuring from the optical centre) - which hopefully puts it away from the glass bits - and most of the energy goes straight through.

    I'd be somewhat wary of substituting the screen material - With front projection, you've got diffuse reflection from your screen / paper or whatever you're projecting onto.
    With back projection, as here, you're relying on the screen material preventing 'straight through' transmission; Looking at the eyepiece without the screen would be a Bad Idea, so I suspect a poor screen choice could also be dangerous...
    Last edited by jerryTheC; 03-27-2017 at 11:43 PM.
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    Default Re: The "Sun funnel"

    Quote Originally Posted by UlteriorModem View Post
    Something I am confused about. There is no filter on the objective end? Wont you cook the eyepiece?
    That and the diagonal was my original thought. However by using an old 20mm eyepiece I figured I would give it a try. After setting everything up and using it for a couple hours I checked for any excessive heat build up and I couldn't feel anything that I would call "hot".

    As JerryTheC mentions. Be sure to use the recommended materials for construction!
    Gordon
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    Default Re: The "Sun funnel"

    Quote Originally Posted by UlteriorModem View Post
    Something I am confused about. There is no filter on the objective end? Wont you cook the eyepiece?
    Quote Originally Posted by ghswen View Post
    That and the diagonal was my original thought. However by using an old 20mm eyepiece I figured I would give it a try. After setting everything up and using it for a couple hours I checked for any excessive heat build up and I couldn't feel anything that I would call "hot".

    As JerryTheC mentions. Be sure to use the recommended materials for construction!
    I tried this for the Venus transit back in 2012 and learned that it is best if the eyepiece is sized a bit larger than the calculation calls for, i.e. use a 12.5mm instead of a 10mm. It also helps if the eyepiece is metal construction as plastic melts And as long as the mount you have the scope on has a 'solar' rate tracking option you should be OK with adjusting the aim every 10-15 minutes, shorter intervals if you choose higher magnification.
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