How to Make a Refracting and Reflecting Telescope

Telescopes are tools for exploring our world and other worlds.

Telescopes spark the imagination. They bring distant worlds near, allowing us to watch birds without disturbing them and see other planets without needing a spacesuit. There are dozens of types of telescopes, but they all are designed to collect a lot of light, then make it easy to look at the image created by all that light. The basic design rule is to focus distant light down to a point with an objective lens or a primary mirror, then magnify that point with an eyepiece.

Things You'll Need

• Two-inch diameter, 300 mm focal length lens
• 10-mm diameter, 50 mm focal length lens
• Four-inch diameter, 400 mm focal length mirror
• One-inch X 1.5-inch elliptical flat mirror
• 10-mm diameter, 35 mm focal length lens
• Holder for the small mirror
• Mounting tube large enough to fit the large diameter optic
• Small adapter tube to fit the smaller diameter lens

Instructions

Making a Keplerian Refracting Telescope

1. 

   A demonstration telescope is easy to make from inexpensive parts.

   Put the small 50-mm focal length lens in the adapter tube.

2. Put the 300-mm focal length lens in the large mounting tube.

3. Measure along the mounting tube a distance equal to the sum of the focal lengths for the two lenses, 350 mm.

4. Insert the adapter tube in the mounting tube so that the small lens is 350 mm from the large lens.

5. Look through the telescope and gently slide the adapter tube to focus the telescope.

Making a Newtonian Reflecting Telescope

1. 

   Not every reflecting telescope needs a mirror this size. A home-built Newtonian is a little more manageable.

   Insert the large mirror at one end of the mounting tube, reflective side facing the inside of the tube.

2. Measure 335 mm from about the center of the mirror and cut a hole in the side of the mounting tube large enough to fit the small lens adapter tube.

3. 

   Although small mirrors are easier to build with than monsters like this one, reflecting telescopes are not that easy to assemble.

   Place the small flat mirror mount at an angle of 45 degrees so its center is at the same height as the hole for the small mirror mounting tube.

4. Insert the 35-mm focal length lens in the adapter tube, then put the adapter into the hole on the side of the mounting tube. Slide it slightly back and forth to focus the telescope.

Tips & Warnings

• The projects described here represent only one possible set of optics for making the telescopes. Many other choices will work equally well.

• The quick, easy and inexpensive refracting telescope described here is appropriate enough for the inexpensive lenses available. But optical quality mirrors are more expensive, so you might want to invest in some machined parts. And the reflecting telescope is just harder to put together anyway, so machined parts can help.

• A telescope collects many times more light than the human eye: Do not point it at the sun! The eye's safety mechanisms can't handle that much light, and your sight will be damaged!

References

• Astronomy Notes: Types of Telescopes
• American Museum of Natural History: Building a Simple Refracting Telescope
• NASA: Build a Telescope

Resources

• TelescopeMaking.org: Mark's Notes for the Amateur Telescope Maker