How to Make Newton's Telescope
Although Newton did not invent the reflecting telescope, he was the first to build a mirror-based telescope free from major design flaws. Newton's telescope, using a concave mirror to collect light from the stars, was able to avoid the problem of chromatic aberration common to earlier refracting telescopes. Newtonian telescopes have many advantages, even today. The telescopes are sturdy, relatively easy to build and compact, allowing for telescopes that you can use in any location.
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Things You'll Need
- Concave mirror
- Measuring tape
- Telescope tube (PVC piping, wood or heavy cardboard)
- Mirror brackets
- Screws
- Small flat mirror
- Small cardboard, PVC or wood tube
- Convex lenses
Instructions
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1
Choose the size for your primary mirror. Newton used a metal concave mirror of about two inches in diameter. Modern concave mirrors are usually made of glass or coated with aluminum.
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2
Determine your primary mirror's focal length. Shine a bright light at the concave mirror and use a vertically held piece of cardboard to find the spot where the reflected light is the brightest. That is the focal point.
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3
Make the main telescope tube. The length of the tube needs only to be longer than the primary mirror's focal length, and the tube should be only slightly wider than the diameter of that mirror.
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4
Attach the primary mirror snugly in one end of your telescope tube. Use brackets screwed into the tube to hold the mirror without damaging it.
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5
Fix a flat mirror at a 45-degree angle within the tube. This diagonal mirror must be at the location of the primary mirror's focal point.
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6
Build the observing tube above the diagonal mirror. This is a small tube rising vertically from the main tube, the width of your observing lenses. Use glue to connect the tubes securely.
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Insert your magnifying lens into the observing tube. Although any convex lens will work, you will get the best results with commercial telescope lenses. Secure the lens with a screw in the observing tube: tighten the screw to hold the lens, loosen it to release.
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Tips & Warnings
Most commercial concave mirrors come with the focal length labeled on the side of the mirror or on the packaging. Use this as a reference when determining focal length.
Close the non-mirror end of the tube with any opaque substance in order to keep all extra light away from the primary mirror.
Images reflected by a concave mirror are inverted so be prepared for all observations with a Newtonian telescope to be upside down.
