Galileos first telescope was two lenses and a leather tube. My first was pretty much the same thing only with cardboard instead of leather. I paid $10 for it at Wal-Mart. For much of the history of astronomy, advances in telescope technology has been driven by the efforts and genius of gifted amateurs. Most serious amateurs at some point in their lives will try building a home-made scope. Here's a simple reflector telescope I'm currently working on. Spacing the optics can be very complicated as I'm discovering, but there are plenty of amateur astronomy sites that give you very detailed directions on lining up your lenses and mirrors. I've included a couple of links to some good astronomy sites at the end.
- Sonotube with a diameter 2 inches larger than the mirror (For my scope it's an 8 inch tube for a 6 inch mirror). Got this one at the hardware store.
- Telescope primary mirror (This one's a 6 inch gimme mirror from a friend)
- Mirror cell (I was lucky and this one came already mounted on the mirror)
- Diagonal mirror mounted on spider the size of the sonotube (eBay - $20)
- Focuser (eBay - $35)
- Eyepiece to fit the focuser (home-made from Lens Surplus kit I bought on-line - got 5 really good lenses out of it)
- Sheet of plywood I like 1/2" for sturdiness and sheer heft.
- Two old vinyl phonograph records (Perry Como Christmas and "The Blodger Family Sings Todays Hits")
The Reflector Telescope
To position the spider figure the distance (in this case 38 inches) from the mirror to the center of the diagonal. To figure out where to drill holes for the legs of the spider, measure the cell thickness to the center of the primary mirror, add the 38" we figured earlier to the center of the diagonal, then add the distance from the center of the diagonal mirror straight back to as close as you can figure to where the screws in the four legs of the spider line up. Cut a slot shaped hole for each spider leg so that they are spaced at 90 degree intervals round the top end of the tube. The slot allows the spider screws to slide forward and back so you can center the diagonal and align it with the eyepiece later.
To adjust the mirror and diagonal, simply look down through the empty focuser hole and lining up the diagonal and primary so that you see a centered image of the sonotube opening and the spyder in the eyepiece hole. This could take a considerable amount of fiddling, but isn't that difficult to do, especially if you have a little help.
When everything is lined up, place the eyepiece in the focuser and test it by focusing on a nice bright land target. The finderscope is ready to mount.
Now we're ready to build a mount for the very fine Newtonian reflector we just made.
The Dobsonian Mount
Mark your plywood sheets as indicated in the diagram and cut them out and assemble them as shown in the diagrams.
The Tube Mounting Box
Drill a hole in the center of the wooden circular stage piece and mount the upright support on the stage. Glue a phonograph record underneath the stage centered on the drilled hole. Glue a second phonograph record on the second stage piece and drill through it. Set the top stage on top of the lower stage so the records sit face to face. Bolt the stages together. This allows the stage to rotate smoothly with slight friction.
Cut the bottom off a film canister or large pill bottle the diameter of an eyepiece and drill a quarter inch hole in the center of the lid. This is a simple collimater and forces you to line up the scope with your eye in the exact center of the eyepiece. Now adjust the primary mirror so it appears centered in the secondary mirror (the one on the spider)
Focus the telescope on a distant object, leave it pointed, then align the finder on the same object so the finder points at the same thing the telescope does.
Additional Information Resources
A Homemade Telescope: Mother Earth News
Homemade Astronomy: Larry Brown
Plans for a homemade Dobsonian telescope
(c) 2009 by Tom King
All images (c) 2009 by Tom King