The first practical reflecting telescope was made by Newton before 1700. It is still the easiest to make.
A home-built telescope can show the rings of Saturn and reveal the colors of the stars, and when those visions come through a telescope that you have built yourself, the experience is that much sweeter. Refractive telescopes can be built very inexpensively -- for just a few dollars -- so it's not necessary to worry a lot about fancy mounting hardware. It's a little different for reflecting telescopes, even the simplest Newtonian design. The primary mirror, the most important single piece of the project, is an expensive piece of glass, so it makes sense to invest in hardware that matches.
Instructions
Making a Newtonian Reflective Telescope
1. Select a focal length for the primary mirror. Somewhere between 900 mm and 750 mm is reasonable. Select an eyepiece lens focal length. Somewhere between 15 and 50 mm would be an appropriate choice.
2. The quality of the primary mirror is important, even if it's not a giant like this one.
The primary mirror is the large, light-collecting element of the telescope, so the telescope can be no better in quality than the primary mirror will allow. Select a wave-front quality of lambda/8 or better (better being smaller, such as lambda/10).
3. Place the mirror in the mirror mount, which is sometimes called a mirror cell. Using a permanent black marker, draw short "target" lines at the exact center of the mirror. The mark should look like a half-inch-long plus sign centered on the mirror, except that 3 or 4 mm at the very center should be left unmarked.
4. High-quality cardboard, such as a sonotube used in construction, can make a good telescope tube.
Install the mounted mirror at the end of the telescope tube. The telescope tube can be either high-quality cardboard or metal. If it's not already painted black inside, Paint the inside black and let it dry completely before installing the mirror.
5. Mark the location of the eyepiece focusing tube. Subtract the radius of the mounting tube from the focal length of the mirror. Mark a spot that distance up the telescope tube from the center of the mirror. Don't worry about it being accurate to the millimeter, just measure from a spot on the outside of the tube that is approximately at the height of the mirror center.
6. Cut the telescope tube. Remove the large mirror and cut a hole to fit the eyepiece focusing tube. If the telescope tube extends more than a couple of inches beyond the eyepiece hole, cut the tube shorter.
7. Newton's innovation was to insert a flat mirror for convenient viewing.
Put the flat mirror in its mount and install the mount on the mirror support. If using a spider mount, the spider will be attached directly to the telescope tube at the height of the centerline of the focusing tube. If using a mirror stalk, it will be attached directly to the focusing tube.
8. Install the focusing tube and replace the primary mirror.
9. Center the eyepiece lens on the adapter mount. The adapter mount will fit into the focusing tube. If the eyepiece lens is more highly curved on one side, face that to the outside of the mount.
10. If desired, align the telescope. See the next section for alignment instructions. (Alignment is highly recommended.)
11. Insert the eyepiece lens in the focusing tube. Use the adjustment mechanism on the tube to focus the telescope.
Aligning the Telescope
12. You don't need a laser pointer this powerful to align your telescope.
Shine the laser pointer directly through the center of the focusing tube. Laser collimators are available to make this job easier.
13. Adjust the position of the small flat mirror to center the laser spot.
14. A target mark makes alignment much easier -- because it's underneath the flat mirror, starlight will never touch it.
Adjust the angle of the flat mirror so that the laser spot falls in the center of the target marked on the primary mirror earlier.
15. Adjust the angle of the primary mirror so that the laser spot is reflected right back to the laser.
