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Stargazing Concave mirror telescope

  1. Mar 14, 2009 #1
    hello,

    I found a concave mirror telescope in my town
    I think that it is very good for making newton telescope
    Estimated length of 20 cm
    I will make a telescope , but I have a problem , I do not know the place of the focus
    and the place of secondery mirror; after focus or before

    can you help me please!
     
    Last edited by a moderator: Apr 8, 2009
  2. jcsd
  3. Mar 14, 2009 #2
    Any replay
     
  4. Mar 17, 2009 #3
    any replay
     
  5. Mar 17, 2009 #4

    russ_watters

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    Staff: Mentor

    Point a flashlight at it and use a piece of paper to find the focal point, then do the math to find the focal point for infinity.
     
  6. Mar 18, 2009 #5
    thank you russ watters
     
  7. Mar 21, 2009 #6
    I have a chunk of glass I bought at a garage sale for $3.00. It is 22" diameter and 2" thick, and is concave on one side (I didn't know this until I took it home and cleaned it off). It has a focal length of 2 meters, and is unsilvered. I have been using it as a small coffee table since about 1970. What was the mirror for?
     
  8. Mar 21, 2009 #7

    mgb_phys

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    Science Advisor
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    Probably a telescope mirror, 60cm f3.5 would make a reasonable Dobsonian cheaply.
     
  9. Mar 22, 2009 #8
    can you help me in the tube of telescope , can it be by plastique or keybord or fe
     
  10. Mar 22, 2009 #9

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Whatever will keep out extraneous light and is not heavy. Probably a thin plastic tube would be best. Use whatever you like to reinforce it and support it from the outside.
     
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