Telescope Vanes

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Xmo1, Jul 21, 2018.

  1. Xmo1 Registered Senior Member

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    There's no reason to have 4 secondary mirror vanes. I could easily done with 1 strut, with adjustments done on the mirror mount.
     
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  3. James R Just this guy, you know? Staff Member

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    Are you sure?

    Vibrations of the secondary mirror are undesirable, for example.
     
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  5. Xmo1 Registered Senior Member

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    With all the materials available today it shouldn't be a problem. Suppose the support were made of titanium - thin and rigid, or a graphite composite - light weight. It depends on the size and composition of the scope I guess about what material to use. But I don't see any reason for four vanes that obstruct incoming light. One should be enough given that the scope chassis could support it.
     
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  7. Goldtop Registered Senior Member

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    You could try with one vane, but I think you're going to have problems trying to center it in the upper cage. The vanes themselves don't really take away any light gathering potential with the primary mirror, hence the work you put into a single vane, if successful, may be a diminishing returns kind of project, not worth the trouble.The secondary mirror itself blocks a lot of light entering the cage, if you can find a way to solve that problem, you could make a million bucks. Let us know how it goes.
     
  8. Xmo1 Registered Senior Member

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    That should be fairly easy. Why use mirrors. Use a lens focused on a (software for aberrations) ccd camera remoted to a screen should do it. Or, replace the secondary mirror with a camera. Why Neutonian telescopes - for nostalgia?
     
    Last edited: Jul 26, 2018
  9. DaveC426913 Valued Senior Member

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    Your single vane will have a very tough time being as stable is 4 vanes, no matter how rigid and light it is. It won't be the vane body where you have problems, it will be where the vane joins the chassis and the 2ndary mirror. Your vane could be infinitely rigid, but that won't stop it from wobbling at the joint. Unless you add more structure to the joint - which will negate all your savings.

    A single vane has only its own width - (what? A millimetre?) as a brace to prevent movement. A vane that spans the chassis' diameter (150mm?) has the chassis' entire diameter as a brace.

    Additionally, not to mention vibrations, a single vane will be far more easily knocked out of alignment and would need constant re-tuning. Again, the joints are the problem, not the vane body.

    Don't forget - no matter how light the vane may be, you're balancing a heavy piece of glass on the end of it.

    If your solution is to use thin, rigid materials of titanium or carbon-composite, why not just use those materials to make 4 very thin vanes? They'll block no more light than one fatter vane - while also preserving the rigidity of 4 vanes. i.e. you get the best of both.
     
    Last edited: Jul 27, 2018
  10. James R Just this guy, you know? Staff Member

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    Making large lenses is difficult and expensive. They are also heavy and tend to sag under their own weight.
     
  11. Goldtop Registered Senior Member

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    I've built a number of truss dobsonians for myself and others when I was building scopes and eyepiece cases as a side business. Perhaps, I'm not really understanding you're design, have you got a pic or something show it?
     
  12. el es Registered Senior Member

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  13. Xmo1 Registered Senior Member

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    Why not mount something the size of a phone camera over the mirror at the mirror focal point. Adjust the focus in software. Use a single rod to hold it in place. Considering phone cameras are high res shouldn't something like that work? A small camera would be a small fraction of the size of the secondary mirror mount. My camera is mounted over the eyepiece, but that seems klutzy.

    While I'm at it: The old low-tech solar scope in Hawaii that used a tube, and a light table should be an affordable way for people to view the sun, rather than buying an expensive scope and solar filters. The size could be scaled down dramatically.

    Next, to answer the over-sized mirrors: Glass mirrors are a thing of the past right? A common parabola, and some kind of mirror material should suffice. I should be able to make a 1 meter scope with a small (phone) camera in place of the secondary mirror dirt cheap. The most expensive part would be the chassis. Wouldn't you think?

    Might be interesting to see how cheap, accurate, and large people can make telescopes with materials available on amazon, or other common stores. A one meter 20lb scope at less than $100 would be amazing, especially one that could take pictures using software filters.
     
    Last edited: Jul 27, 2018
  14. DaveC426913 Valued Senior Member

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    What does "Adjust the focus in software." mean?

    Do you mean literally capture an out-of-focus image with the camera and correct the focus with software? This cannot be done. You cannot correct information that is not there.*

    If you mean adjust the focal length of the camera, then there's no need. It should always be set to infinity.

    This is a completely different kettle of fish. You might want to start with deciding what problem you are trying to solve. It seems like you;re throwing darts at a wall.

    What is this "mirror material" of which you speak?

    You talk as if you assume no one's ever tried to improve scopes - as if our best scope technology is decades out of date - instead of the 21st century technology it is. You might want to start with examining what methods have been tried - such as a mirrored parabola - and why they don't quite work the way you might think.



    *When I worked in a photo lab (paper, chemicals), a woman brought me some out-of-focus pictures and the negatives. She wanted me to "correct" the focus so they were sharp. When told this cannot be done, she was perplexed. After all, I had this giant machine that focused the image from the negative, why couldn't I just re-focus it?
     
    Last edited: Jul 28, 2018
  15. Goldtop Registered Senior Member

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    That sounds great, can't wait to see the prototype, when do you plan on building it?
     
  16. billvon Valued Senior Member

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    Sensitivity. Ability to use multiple sensors. Filtering.
    Then you lose resolution. There's no such thing as a free lunch.
    Try it!
     
  17. Xmo1 Registered Senior Member

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    I was watching a video on graphene. Stronger than steel and few atoms thick, the manufacturer had a 50gal cardboard drum of it where the drum far outweighed the material. It could be formed into a shape to support a mirror-like coating.
     
  18. DaveC426913 Valued Senior Member

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    All materials have their weaknesses as well as their strengths.
    You'll want to be checking the type of strength. "Stronger than steel" is ambiguous.

    Concrete, for example is extremely strong when it comes to compression, but very weak under tension.
    A parabola made of graphene may not be strong in terms of torsion and deformation - it may not hold its shape very well.
     
  19. Write4U Valued Senior Member

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    Perhaps in a computer programmed adjustable multi mirror capture organization system in the telescope? Something like an electronic version of a Linhof camera.....

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    Actually software driven auto-focus cameras are abundant today.
     
    Last edited: Aug 15, 2018
  20. DaveC426913 Valued Senior Member

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    9,198
    Telescopes are not cameras.

    The need for an astronomy telescope to focus any closer than infinity is ... exceedingly rare - and very brief.
     
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  21. Write4U Valued Senior Member

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    Unless the telescope is mounted on a satellite or spacecraft and needs to be controlled electronically for correction of any abberations.
     
  22. DaveC426913 Valued Senior Member

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    That's not focus.
     
  23. Write4U Valued Senior Member

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    True....and farfetched as well. I was trying to say that today's cameras have very sophisticated electronic auto-focusing and auto-exposure calibrations. Auto-sensing is becoming an every-day convience in many functional applications.

    But Telescopes are by definition for extremely long distances and are preset to infinity. Simple.
     

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