Now you too can be Galileo! Inspired by Cosmos and the recent eclipse, this refractive telescope gives you a Galileo experience out of things you may already have around the house, or at worst $20. There are two versions - a fairly impressively decent handheld telescope you can look through, and a camera lens version which works like a powerful (though fuzzy - depending on quality of the lenses) telephoto lens. The lenses used are 40.5mm filter-style close-up lenses - the type that screw on to the end of a camera. Cheap lenses give a beautiful low-fi look with purple chromatic aberration.
To build, you'll need a 60mm inner diameter cardboard tube, like the Tu2 Mailing Tube from Australia Post. This tube needs to be cut down to about 60cm long for the handheld and about 50cm for the camera version. You'll also need a 40.5mm +2 Close-Up filter, which you can get on ebay pretty cheaply, and for the handheld version you'll also need a +10 Close-Up filter. A kit of four filters including those two go for about $17 on ebay.
Future ideas: fully 3d printed body, improved focusing, kit version with everything shipped inside the tube, cheap reflector telescope, rotating mounts, mounts for different cameras
Print with no raft or supports. For a small improvement, lightly spray the inside of the tube with black matte spraypaint and leave in open air to dry for a day.
For the Camera version, cut your tube to be about 50cm long (go a little longer then trim it down with scissors till it's in focus). Print one of each of the camera and lens end caps.
For the handheld telescope, print two lens end caps and screw in a +2 Close-Up filter on the far end, and a +10 Close-Up filter on the part you look in to. Look through the tube, point it at something interesting, then move it away from your face and watch the blurry dot expand to fill the lens completely. The image will be flipped, just like Galileo's original telescope! Note you can also make the handheld version without a 3d printer by cutting holes in the rubber end caps that come with the mailing tube, and putting the lenses in to those, but it's a little less secure so be careful you don't bang the telescope or the lens could pop out. In the photos of my telescope I'm actually using that style, because I made it in a few hours and didn't have time to design and 3d print ends.