Specialty Galilean Telescope (about 20x Magnification): Construction

Specialty Galilean Telescope (about 20x Magnification): Construction

The most important determination you will want to make is how great your magnification. We opted for a magnification of 20x, which resulted in a longer telescope than we could find from an office supply store. As such, we decided to switch the bulk of the body to a PVC pipe. The material and tools for this project are:

PVC pipe:
  • Outer tube (diameter: 5 cm or 2 inches; length: 2 meters or 7 feet)
  • Inner tube (diameter 4 cm or 1.5 inches; length: 15.25 cm or 6 inches)
Note: Our photos show flexible piping, which we started out with, but upon completion we preferred a straight pipe

Paper towel or toilet paper tube
Extra cardboard
  • Concave-convex lens: Diameter 49 mm, focal length 100 mm
  • Plano-concave lens: Diameter 47 mm, focal length 2000 mm
Note that the focal length of our lens are 2000/100 = 20, leading to a magnification of 20x.
Our lenses were 47 and 49 mm, or 1.8 and 1.9 inches, while the only PVC pipe we could locate came with an interior diameter of either 1.5 or 2 inches. We purchased flexible PVC pipe with an interior diameter of 1.5 inches, which was small enough to slide into the larger pipe.

Note: We chose to forgo standard PVC pipe of 1.5 inches simply because it only came in 10-foot lengths, while the flexible pipe did not. However, the flexible pipe came slightly curved, a problem we thought would change with sufficient exterior pressure and/or enough time inside of the straight pipe. In retrospect, we probably should have gone with the standard pipe and kept the excess around for future projects.

We attempted a couple of different methods of securing the lens and the pipe. We found success with a toilet paper tube, though a paper towel tube should also be effective. We slid the eyepiece lens into the tube, working carefully to make sure that it was straight.

The cardboard tube still fell short of the PVC diameter, so we added cardboard spacers along the side. Gluing the spacers in place allow the eyepiece to be adjusted as necessary.

The flexible PVC pipe was trickier, and the problem won't be resolved if you use a straight length of pipe. We used a boxcutter to scrape along the inside of the entry to the pipe to create a smooth area large enough to just slip the objective lens into.

Once you have the two complete segments, it is time to put them together. Slide the smaller tubing into the larger diameter 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. PVC connectors, also purchasable at a hardware store, can serve to connect the two.

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