1) Cylindrical cardboard (1 small and 1 bigger in diameter)
2) Insulation tapes
3) Concave and Convex lens (1 small and 1 bigger in diameter)
Step 1: Get the Lens of Correct Diameter
One larger Convex lens and one smaller Concave or Convex lens – this must be smaller than the tube you are going to use. If the smaller lens is a convex lens it will give you the same view but turn everything upside down. I got one from Amazon and the other from my VR Headset.
Step 2: Body of the Telescope
Two cardboard tubes in which one fits perfectly inside the other. Please make sure that no light enters through the setup unless it is through the two openings, else it will distort the obtained image. I used a badminton racket bottle and chart paper.
Step 3: Fix the Lens at Both Ends
Fix the larger lens at the end of the cardboard with the largest diameter and the smaller lens at the cardboard with the smaller diameter using insulation tapes.(on both ends)
Adjust the smaller cardboard piece by sliding it in and out till you get a clear focus on the extraterrestrial bodies.