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Stargazing I want to build my telescope any advice ?

  1. Sep 19, 2006 #1
    i am into astronomy as a hobby and i noticed as i was looking for telescopes that the telescopes u buy are not that flexible and that u have to buy a telescope for each type of observong ( to have the best quality of course).
    so i made up my mind to build my own telescope(a refractor) that has 2 variables :
    1)the lenth of the tube , and thus the focal lenth (because i can put different lenses in it)
    2)the apreture (as in put a diaphragm that would reduce or maximize the amount of light i get).

    i made blueprints and all , and before i start id like to see if any of u has any additional information or modifications to give me that would let me fix my model if it has any bugs.
    start by giving me ur opinion about wat i said and ill post more for more details.

    thx in advance , and long live astronomy :biggrin:
  2. jcsd
  3. Sep 19, 2006 #2


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    Gold Member

    Telescopes do this. For low vis objects (almost all of them), you use the scope at full aperature, but for very bright objects such as planets and the Moon, you can put a cap on the objective end of the scope to reduce the light.
    Why? Why not just get different lenses?
  4. Sep 19, 2006 #3
    It might be a good idea to post your blue prints.
  5. Sep 19, 2006 #4
    Further to Dave's comments:-
    You really should use the maximum of your telescope's aperture as much as you can - the resolving ability (How fine the detail you can make out) of a telescope is directly dependent on the aperture - more aperture = higher resolving (finer detail) ability
    You can get about 2x magnification per mm of objective diameter - so for example, if you are using 100x magnification - don't stop the scope down to less than 50mm diameter, otherwise you will impact on the scope's resolving power.
    If you really want to dim the image more than that - a variable polarising filter is the best way to go
    If you want to lengthen the focal ratio - use a barlow lens

    If you simply want to vary the magnification - then as dave says, just get a selection of eyepieces - magnification is a direct function of the focal length of the telescope's objective lens, divided by the focal length of the eyepiece you use.
    So - a scope with focal length of say, 1000mm, will give you 40x if you use a 25mm eyepiece (1000/25 = 40)
    To get, say 100x from the same telescope - just use a 10mm eyepiece (1000/10 = 100)
    4mm eyepiece - 1000/4 = 250x
    etc, etc.......
  6. Sep 20, 2006 #5


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    Ambitious project. My biggest concern would be the handling and mounting of interchangeable lenses. The primary lens is the most critical piece of a telescope and interchangeable lenses are just asking to get damaged. In addition, it would be tough to securely mount them and keep them properly aligned, while keeping them interchangeable.

    I don't really see an advantage for interchangeable lenses over just having two fully separate optical tubes - and that has some big advantages, such as the ability to autoguide when you piggyback them.

    I just bought a big SCT - they are pretty versatile in that you can shorten the focal length by adding a focal reducer or lengthen it by adding a Barlow. But for short focus deep-sky, I'll likely end up piggybacking a refractor on it.
    Last edited: Sep 20, 2006
  7. Sep 20, 2006 #6


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    Russ is right. I owned a series of telescopes over the years, but about 20 years ago I decided to optimize, and I bought an Astro-Physics 6" f:8 APO refractor for a main scope and a Vernonscope 80mm f:5.6 APO as a finder/guidescope. Of course that 'scope can be used on it's own, too, if I don't feel like hauling out the "big gun". I have 6" Schmidt-Newtonian for really wide-field stargazing, but sold my catadioptic scopes. I am hooked on refractors. You might wonder how I can use such a short APO as a guidescope, but it's pretty easy with a well-mounted Barlow and a short f/l guiding ocular. Of course, when you put in the 2" mirror diagonal and a 55mm 2" ocular, that little scope is a wide-field wonder. The cost of a refractor is mostly in the objective, not the tube and focusser, so it won't cost you much more to have two entire optical tube assemblies AND you can use them together if you choose them properly. Then, spec out a mount that will support the weight of both of them securely.
    Last edited: Sep 21, 2006
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