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Space Hardware

Suggestions for a Home-Built Telescope 37

Posted by Cliff
from the stargazing-on-new-year's-eve dept.
hodet asks: "I would like to know if anyone here has built or are planning to build their own telescope. My plan right now is to build an 8" F/6 Dobsonion Reflector based on these plans. The same design can also be found here. The base has been cut and the primary and secondary mirrors are to be ordered shortly. Since I plan on making a few modifications to this design I'd like to know if anyone here has done anything similar or totally original and what thoughts and suggestions you may have. I know it may be cheaper and easier to buy one from Meade, but that's not what I'm looking for."
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Suggestions for a Home-Built Telescope

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  • Make vs. Buy (Score:5, Insightful)

    by DynaSoar (714234) on Wednesday December 31, 2003 @12:34PM (#7845820) Journal
    I've made a 6" reflector, and I've bought one. You don't make a telescope to have a telescope, you make it to make it. It's the process that's important. The fact that you end up with a telescope is almost secondary. It's sort of a spiritual thing, when you spend hours and hours grinding, and consider those who've done the same over the centuries.
    • Re:Make vs. Buy (Score:3, Insightful)

      by Glonoinha (587375)
      24 comments and nobody has offered up a way to overclock this thing yet? Heck, the only reason I read it was to get a grasp of just how bad /. was going to crank this guy's handle : simple ways to create a 48" parabolic back mirror, ways to create a 48" diameter tube for that mirror, maybe someone would come up with a four bounce set of mirrors set up between two houses as a way to use even larger mirrors or a longer focal length or a wider field of view ...

      Surely somebody is going to figure out a way to
      • Glonoiha sez: "24 comments and nobody has offered up a way to overclock this thing yet?"

        You don't want to overclock a telescope. They have to be perfectly clocked to work. And actually, as two different /. articles in 3 days have pointed out, the earth is running slow in its orbit, so he might actually need to underclock it for it to work right.

  • a few links (Score:3, Informative)

    by Councilor Hart (673770) on Wednesday December 31, 2003 @12:36PM (#7845839)
    can be found at dumbo [ugent.be]
    Although a few might be outdated.
    Good luck.
  • Focuser (Score:2, Informative)

    by Uma Thurman (623807)
    Instead of making a focuser, you might be happy buying a really nice one instead. Out of everything you put on the scope, the focuser and the mount will be either a source of pleasure, or a source of annoyance. A good focuser will make it much easier to get the best views of the stars, and proper balance and stability of the mount will make it easier to point the scope.

    It really makes a difference, more than anything else.

    http://www.scsastro.co.uk/it060013.htm
    • Re:Focuser (Score:3, Informative)

      by battjt (9342)
      Dad built a new mount for his 13" dob that was lighter than the original.

      He started with the standard cardboard tube, but other than that tried to make it as light as possible for mobilility.

      What he found was that ballance isn't so hard, just use large washers for counter weights, but the lightweight scope jiggles more that the heaver scope. Also the force to break the teflon bearings loose jars everything more when there is less mass to move.

      Joe
  • My recommendation:

    Spend as much as you possibly can on your lens or mirror, and as little as you can on everything else. The rest of the materials dont matter much, but if you optics aren't up to scratch, the whole thing is useless.

    • Re:Optics (Score:3, Informative)

      by seanmeister (156224)
      I beg to differ - the mount is very important also. Top-of-the-line optics won't do you much good if you can't aim the telescope because it's all attached to a shaky mount. The dob mount design itself is solid - just don't skimp on the materials used to build it.

      Sincerely,
      a guy who recently bought a telescope with a shaky mount
    • Spend as much as you possibly can on your lens or mirror, and as little as you can on everything else. The rest of the materials dont matter much, but if you optics aren't up to scratch, the whole thing is useless.

      Good advice. A decent sonotube and plywood Dob mount is ridiculously simple to put together, and, unless you've really screwed up, will be stable. I can't imagine how you'd screw it up, but I suppose it could happen.

      I threw one together last year, an 8" f/6. I used 16mm film cans for the alt

    • Mirror mounting and general construction quality are also very important. It doesn't go any good to have a 1/8 wave mirror with significant astigmatism caused by a bad mirror mount.

      Mirror cooling is also important, as well as good baffle design (not to mention the consequences of making the tube the wrong length).

  • My brother, Norm, wrote a book with Dobson, which is unfortunately out of print now. I copied the following from the net. It should be useful if you can find it: "How and Why to Make a User-Friendly Sidewalk Telescope" by John Dobson with Norm Sperling 169 pages; 154 clear,friendly line drawings; 9 photos. Hardbound in plywood (Dobson's favorite material) Exclusive source. $39.95
  • I own a celestron 8" dob. The big thing you need to consider it potability. You aren't going to be leaving it out in the middle of your yard, so every time you want to use it you are going to have to move it around. Consider adding some locking caster wheels. Handles are another nice thing. Think about how it is going to fit in your car
    • Re:a few suggestions (Score:3, Informative)

      by battjt (9342)
      Dad has a 13" dob. He put kid's bike tires on it. To move it, he locks the tube in the base with a wing nut and bolt, then tips the whole thing over onto the wheels.

      Before this, when I was in high school, he would wake me up at 3 am to help him put the scope away. (now I'm 32)

      Joe
    • I saw one guy mount his Dob in a wagon, the same type of red wagon you may have had when you were a kid. Great for someone who observes mostly from their yard. Roll it out into the yard to observe and back into the garage when done.
  • by Dammital (220641)
    There are some interesting photos and information on Tom Droege's TASS [tass-survey.org] site. Not sure how active they are at the moment, but there are some knowledgeable people there.
  • "Always keep your optics clean."

    And remember that revenge is a moral imperative.
  • Other options (Score:3, Informative)

    by pease1 (134187) <bbunge AT ladyandtramp DOT com> on Wednesday December 31, 2003 @02:39PM (#7846981)
    While John's design is good and will work great, there are others - many others. One good source is this book [willbell.com].

    Build the scope yourself, don't spend all that much money on the focuser (better yet make your own focuser) and spend the saved dough on additional eyepieces. You can get a "better" focuser later.

    A 6-inch f/8 scope is a wonderful starter - much better then the junk you find in stores. Hundreds of deep sky objects, craters on the moon, moons of Jupiter and rings are Saturn are all easy to see.

    Final advise. Locate and join your local astronomy club, go to a regional star party (can you find both here [skyandtelescope.com] and get out under dark skies.. sorry, this requires getting out of the city.

  • I've made a 4" f/8 Dob. The mirrors and focuser where from Orion. The tub is a 5" PCB pipe, the base is made out of wood. Before I made this, I bought a 8" Dob from Orion(the XT8). It was fun making the 4" but it can't compare to the quality of the 8" I bought. The 4" is a WAAAY better than telescopes you'll find in department stores, however it was the little things that make it not as nice to use as the 8". I needed counter weights and I have a little problem with friction with my mount. I've had to make
  • by NanoGator (522640) on Wednesday December 31, 2003 @03:06PM (#7847283) Homepage Journal
    "Suggestions for a Home-Built Telescope"

    Move into an apartment complex with attractive tenants.
  • Consider frensel lenses. You can get a very large Frensel lense at a relatively cheap price. They cause eye-strain if you look through them for very long periods, but how long are you going to just sit there staring through the telescope?
    • I hope this is a joke. You should not even consider using optics with 1000+ wavelength rms error instead of 1/4 wavelength rms error (achievable with a well mounted mirror).

      Fresnel lenses are fine for solar furnaces and the like, but not useful in telescopes.

  • by ghamerly (309371) on Wednesday December 31, 2003 @05:05PM (#7848369)
    I made a a scope from these plans -- pretty much the same scope that you want to build (8"). I built it in summer 2002. You can see my scope (including pics) here: http://www.cs.ucsd.edu/~ghamerly/personal/astro/te lescopes.html [ucsd.edu] I have some advice on this page, which I will repeat/expand on here:
    • For me, making the telescope was all about the experience of learning & having a project -- not saving money. I believe I could've bought a better telescope for less money than I spent on making mine (not including the cost of time spent).
    • The plans are quite good and complete -- though I still had to improvise quite a bit when I didn't have exactly the same materials. However, improvising turned out to be some of the most fun, since it was problem-solving.
    • On a more technical note, one of my improvisations forced me to place the secondary mirror closer to the main mirror than it really should have been, therefore I lost about 3/4" of the main mirror. This is something to be aware of. This was mostly due to my naivete, and the plans don't really mention this issue. When placing the secondary mirror, take time to really consider your main mirror, focal length, and *the size of your secondary mirror*.
    • The mirror collimation design (3 bolts on a board) works really well, I think, for how simple the design is.
    • I bought my mirrors from E-scopes [e-scopes.cc], and was happy with them. I bought teflon from Rob Teeter at Teeter's Telescopes [teeterstelescopes.com], and I recommend them.
    • The tube can be had from a local construction surplus store -- it's called Sonotube (brand name) in the industry, and it's used to pour concrete pillars. I was afraid that 1/8"-thick would be too thin, and I considered going with 1/4", but 1/8" turned out to be fine (and much lighter).
    • I'm extremely happy with my telescope, and while it isn't perfect, I had so much fun making it, and it's so easy to use. I had no sooner finished it than I wanted to make a larger one. :)
    • Here are 6 pictures taken of the moon with this telescope (just holding my camera up to the eyepiece with my hand): 1 [ucsd.edu] 2 [ucsd.edu] 3 [ucsd.edu] 4 [ucsd.edu] 5 [ucsd.edu] 6 [ucsd.edu]

    Good luck, and have fun!

    • Great advice, thanks. Checked out your site, very cool scope.

      Our club had an ATM workshop in May and we tested the true focal length of a mirror and then used Newt [att.net] to plugin the values which calculated the proper distance the secondary mirror should be from the primary mirror. Values included, the size of the and the travel of the focuser, focal length of mirror and the size of the secondary to name a few. I was surprised by the fact that a mirror advertised as F/6 may not be and you have to test it wh

  • by Anonymous Coward
    I do not remember it exactly, but ...
    It is faster to build a 4" and then an 8" telescope than it is to build an 8" telescope.

    I use this frequently when I am trying to convince someone to build prototypes before doing a full fledged system.
  • by justanyone (308934) on Wednesday December 31, 2003 @09:18PM (#7850259) Homepage Journal
    If you want a large but immobile telescope, there's a way to do it with a large spinning pool of Mercury. Some canadian university built a nice observatory doing this.

    The limitations are that they have to wear breathing protection around it due to Mercury outgassing vapor and them (understandably) wanting to avoid heavy metal poisoning.

    However, it apparently makes a wonderful mirror, albeit a parabolic one. It would be interesting if someone could set up a manufacturing process whereby we would spin up Aluminum as a mirror base then spray a thin layer of Silver or chromium onto it to give a polished surface.

    Of course I don't know jack about mirrors except that grinding glass ones is a pain in the butt and therefore costly.

    Anyone know more?
    • It would be very difficult to maintain an accurate surface in aluminum. The current state of the art (afaik) in exotic mirrors is thin carbon-fiber composite mirrors molded on a mandril, then silvered.

      The fast majority of homebuilt telescopes are built using glass, pyrex or zerodur (all glasses of various compositions) mirrors. All newtonian telescopes f/8 or slower can sometimes be made with spherical mirrors, everything faster than that requires a parabolic mirror.

      Many amateurs polish their own mirror

    • According to my Astronomy professor (who also doubles as a english professor, so take this with a huge grain of salt), almost none of the large telescoped have glass mirrors. They spin molten aluminum and, as you say, spray a thin layer of polishable metal on the surface. This metal is them polished into its final shape.

      The main reason they use aluminum is that glass is so heavy, it sags under its own weight.

      I have heard of some telescopes using many small reflectors vice one large reflector. Most mode
  • You might want to take a look at Mel Bartels Telescope home page [efn.org]. It contains lots of references on mount design, and a home-brew system for adding computerized goto capabilities to dob scopes.

    Depending on your fabrication skills and facilities, you might also want to look into a truss dobson (probably not necessary at 8"), or a split ring mount. The split ring mount is an equatorial mount, making it easy to add a motor to track objects against the earth's rotation. Even if you want to learn the sky for

  • Mirror Grinding (Score:2, Informative)

    by Ann Elk (668880)
    I know you're planning to buy your primary mirror, but you might like to read Ed Grinds a Mirror [scopereviews.com] from Ed Ting's excellent astronomy site. Also, if you ever need advice on production scopes and accessories (like eyepieces), Ed's site [scopereviews.com] is the place to go.
  • The most important thing in a telescope is the optical alignment. You can have outstanding optics and have it all go to hell if the optics are not properly aligned and collimated. This is especially true of telescope designs with multiple powered optics (such as catadioptrics), but even with Dobsons you still have tip, tilt, and focus to worry about (those Cassegrain designs are very sensitive to errors in alignment of the secondary mirror because you quickly introduce all sorts of higer-order abberations
  • I think you will find that it will be easier to grind a spherical primary mirror rather than a parabolic one. Look here [arizona.edu] for implementation instructions. there will neet to be a resulting adjustment to the secondary optics to compensate for the difference in shape. but the grinding process will be much simpler.
  • I've not built a telescope, but I've got a friend who's made a bunch, who runs TelescopeMaking.org [telescopemaking.org], and in talking with him it seems like the key to success is to find your local telescope making group and hang out with them on their work nights.

    You'll have the experience of people who've already made several, be able to borrow some of their tools, and share parts and ideas.

    Besides which, you'll probably meet some cool people.

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