Personal Readings
How to build a Telescope
When Italian astronomer Galileo Galilei heard rumors of the first practical telescope at the beginning of the 17th century, he was quick to craft his own version and turn it toward the heavens. Following his pattern, you can make your own Galilean telescope at home and use it to study the stars, just as the well-known astronomer once did. A do-it-yourself Galilean telescope makes an excellent and inexpensive starter telescope — or science fair project. It is limited by its small field of view, but can inspire an even deeper study of the stars. A Galilean telescope is, in essence, a tube with two lenses placed at either end. The eyepiece is a plano-concave lens, which is flat on one side and curved inward on the other. The straight side is pointed outward. At the other end is the objective lens, a concave-convex lens, which curves inward on one side and outward on the other. The convex side faces outward. Most of the materials you'll need can be found at office supply stores or hardware stores. However, lenses will likely be your most challenging item to purchase. They can be bought from a variety of sources. Edmund Optics has a variety of high-quality sizes and focal lengths that can be matched to achieve your magnification goal. However, we went with a smaller surplus company that ships, in part because they are relatively close to us (we took the time to get feedback from the owner on our purchasing decisions). Their stock is less expensive, but also somewhat touch-and-go.
Magnification & focal length
A telescope's power, or magnification, has to do with its lenses. Magnification is determined by the focal length of the telescope divided by the focal length of the eyepiece. Focal length is the distance from the lens to the point where the telescope is in focus, and is measured in millimeters. For example, using a 50-millimeter lens on a telescope with a focal length of 450 mm would get you a power of 9x. Generally, the longer the focal length of the telescope, the more power it has, the larger the image and the smaller the field of view. By exchanging lenses, you can change the power of the telescope.
How to Build !!!
Building a simple Galilean telescope (about 9x magnification) :
Building a simple Galilean telescope (about 9x magnification): Cardboard telescoping mailing tube, with an inner and outer tube that telescopes. These can be found in most office supply stores:
.Diameter of 50 mm (about 2 inches)
.Length of 1,100 mm (43.3 inches)
Lenses, which can be purchased:
.Concave-convex lens: Diameter of 49 mm, focal length of 1,350 mm
.Plano-concave lens: Diameter of 49 mm, focal length of 152 mm
Note that the focal lengths of the lenses are 1,350/152 = 8.88.
Tools:-
.Coping saw
.Box cutter
.Drill or electrician's punch
A telescoping mailing tube will have an inner tube that slides freely into the outer tube. Cut two pieces from the inner tube, approximately 1 to 1.5 inches (2.5 to 4 centimeters), to create spacers to hold the objective lens. A coping saw will cut the cardboard clean and straight, which is important. The removable cap on the end of the outer tube will become the eyehole. Use the drill to make an eyehole in the center of the cap, using light pressure. It is important to keep the cut as smooth as possible. An electrician's punch will also serve. Drill small holes around the outside of the inner tube, where the lens will be. Place the flat end of the eyepiece lens against the removable cap. Slide the lens and cap into the outer tube. Add glue through the holes, and turn the lens to spread it around. Press the tube against the lens firmly until the glue is dry. Set aside. Cut the closed end of the outer tube. Determine the how far into the tube the lens and spacers need to sit, then drill small holes on the sides of that region. Slide the first spacer in; insert glue through the relevant hole, moving it slightly to spread it around. Keep pressure on the region until the glue has dried. Once the first spacer is dry, slide the objective lens in, with the second spacer against it. Insert glue through the hole, spread it, and press until it is dry. Slide the inner tube into the outer tube. The telescope can be focused by sliding the cardboard tube as necessary. Once the correct focusing distance is found, the two ends can be permanently attached with glue or tape.