How to Make a Telescope With a Telescope Lens

Got an old telescope lens?

If you have a telescope objective lens lying around, it's easy to put together a simple refractor telescope similar to the one Galileo made for his first observations of the moons of Jupiter. You'll need an eyepiece lens and a tube. Other than some problems with color aberration, refractors are the easiest telescopes to make.

Difficulty:

Easy

Instructions

Things You'll Need

• Telescope objective lens
• Binocular eyepiece
• Long cardboard tube large enough to fit the big lens into
• Double-sided masking tape
• Single-sided masking tape
• Poster board
• Knife or heavy duty scissors
• Long table or board
• Flat black spray paint

Simple Refractor

1. Prop up the large telescope objective lens at one end of a board or table so that the flat side of the lens points toward a distinct object more than 100 yards away. Go to the opposite end of the table with the binocular eyepiece and look through it toward the telescope lens. Move the eyepiece gradually toward the large lens until the image of the focusing object comes into focus. This will be the distance at which the eyepiece should be mounted. Measure the distance between the eyepiece and the telescope lens. Subtract 3 inches and cut the tube to that length. Spray paint the inside of the main tube with black flat spray paint. Cardboard tubes are available at the post office and hobby shops.

2. Wrap the inside of one end of the tube with double-sided masking time. Keep adding turns till the inside diameter is slightly less than the outside diameter of the telescope lens. Carefully push the lens into the end of the tube till it is snugly across the opening, held in place securely by the tape. Make sure the lens sits flat across to the opening of the tube.

3. Roll a six-inch wide strip of poster board into a tube. As you begin rolling the tube make the inside diameter of the tube the same as the outside diameter of the barrel of the binocular eyepiece. Keep rolling layers around the poster board tube until the outside of the tube fits snugly into the open end of the main tube opposite the objective lens. Tape the ends of the poster board to secure the tube. Spray paint the inside of the eyepiece focusing tube with black spray paint.

4. Slide the eyepiece focusing tube into open end of the main tube opposite the objective lens. It should fit snugly, but slide in and out smoothly. Slip the eyepiece into the open end of the eyepiece tube.

5. Point the telescope toward a distance object. Look through the eyepiece and slide the eyepiece tube in and out until whatever you are looking at comes into focus. If you want to steady the telescope, you can mount it on a tripod or some sort of mounting device. A simple pair of legs screwed to the tube will allow you to comfortably use a lower power handmade scope like the one described here.

Tips & Warnings

• A lower power telescope objective with a wider eyepiece, such as one from an old pair of binoculars, can provide more enjoyable viewing than a higher power lens with a narrow focus and low eye relief eyepiece.

• Surplus binocular eyepiece lenses and telescope lenses are often color corrected and can save you the distracting color rainbow effects Galileo had to deal with using simpler lenses.

• Handle the lenses with a fine linen or silk handkerchief or soft gloves to avoid getting oily fingerprints on the glass.

References

• How to Make a Small Telescope
• How to Build a Telescope