Introduction: How to Build a Refracting Telescope

Picture of How to Build a Refracting Telescope

As of late, I've become very interested in space, stars, galaxies, and the universe. Naturally, then, I decided to build a refracting telescope for the creative project in a class I'm taking called "Changing Views of the Universe". 

I'm actually pretty pleased with my build. I ended up getting a good amount of magnification and I can see craters on the moon in an urban area (Washington, DC). Sadly, there were several things that could've been done much better with more time. I encourage anyone interested in building a telescope to check out my process and modify it as they see fit!

Anyway, let's get started!

What you'll need:

1. Two lenses of different magnification. I got one out of a handheld magnifying glass (the smaller in size lens) and from a scientific equipment shop. Make sure the larger diameter one also has larger magnification power. 

2. Two lengths of PVC pipe. I used a meter of 3" diameter pvc and a half meter of 2" pvc (I think). The smaller diameter PVC fit nicely inside the larger one, and, with a little finessing, the lenses fit in each. Make sure each length of PVC is a bit greater than the focal length of the lens.

3. Gaffers Tape. Gaff, Gaft, whatever. It's that wonderful black tape that's super easy to tear, doesn't leave marks, and isn't very shiny.

4. Flat black spray paint.  


1. Exacto knife
2. Dremmel 
3. Hot glue gun

Let's do it!

Step 1: Get Your Lenses Out!

Picture of Get Your Lenses Out!

If you're using a lens from a magnifying glass, get it out using the exacto knife and dremmel. Try to keep the lens from being cut or scratched... things won't look as good later!

Step 2: Paint It!

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The first step is going to be painting. Cover the two lengths of PVC with black spraypaint, and even do the inside. Let it dry for a while... you don't want it to be at all wet for the next step. Make sure that the spraypaint you're using works on plastic.

Step 3: Tape It!

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I actually made the mistake of putting the entire thing together without this initial step, and I regretted it quickly. PVC, even with spraypaint, is really reflective. We don't want internal reflection. The fact that my pipes were pretty small didn't help either. 
Ultimately, I decided that I'd tape the inside of the larger pipe. It's surprisingly easy to do, too. Thread a piece of gaff tape down the pipe and affix it to the edge on opposite sides. Using the smaller pipe that you bought, flatten the tape against the inide of the PVC by sliding the small pipe down the larger one. Make sense? good. Now do that a few times to completely cover the inside.

Step 4: Cut Cut Cut

Cut the larger tube to be about 3/4 the focal length of the powerful lens. The smaller diameter tube should be about double the size of the larger tube that you just cut off. This is going to be really helpful when you focus your telescope.

Step 5: Affix the Lenses

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Hopefully, your internal diameter and larger lens diameters match up pretty nicely. If they're a little off (mine were) use gaffers tape to make the internal diameter smaller, rest the lens on the end of the pipe, and hot glue it in place using a low heat hot glue gun.

For the smaller lens, cut a hole into a pill bottle cap or some other plastic thing that fits nicely into the smaller diameter PVC. Hot glue your lens in the holder, and stick the holder into the telescope.

Step 6: Tape Tape Tape.

Picture of Tape Tape Tape.

Finally, you're going to want to tape the rim of the smaller tube to ensure it doesn't fall into the larger one. I used a few strips of gaff tape that I stripped down the middle. It worked quite nicely!

Step 7: You're Done!

Go check out the moon, the stars, or even a planet! Thanks for reading, feedback is appreciated!


MaryD200 (author)2017-09-28

Building this for the science fair, what did you glue the bigger lense, to and where did you stick the paint cap. How did you dry the pvc so the paint dried evenly, and what did you use the make it stand up?

BigCthulhu (author)2014-11-01

NIce work, my parents' generation made scopes like this in my homeland, in Hungary. There was an astronomer-teacher guy, Kulin Gyorgy, or simply "Uncle Georgie" for those thousands who got helps and assistance from him to build scopes from cheap and simple parts around the house. This old DIY-community was working as a virtual club in Hungary, when the people were under terror by the communism, and almost nobody had enough money to get normal scopes to observe, but a lot of children and adults wanted to look into Universe instead of their misery. Today this era became a part of the history, but we have memories of this scope building method, so I can mention some tricks to improve the image of this scopes we call "simple scopes", or "nut-thrasher".

First never forget, in physics there are not wonders - the simple lens refracts the gathered light, and so it became also a prism; but a prism divides the colours of the spectrum, so this lens will create very disturbing orange and blue, blurry semicircles around the celestial objects (like stars and planets, even Moon), and so you can't set the focus properly, simply because there won't be only one exact focal point of all the divided colours. This is a fact, no way to ignore it...
If you use simple lenses, (which are grinded from only one piece of glass) as objectiv lens (for example the home magnifiers), the result will always be this poor optical quality. But the complex achromates (made of min. 2 parts, different glass materials, with sophistically designed curves and other tricks) may be too expensive for an amateur astronomer, so here are the tricks to improve a bit the imaging of these simple and cheap lenses. But, you know, there are not wonders...

1. Use lenses with larger focal lenght: for example 50 mm diameter and 500 mm or longer focus - if the focal ratio is more then 10, the colouring effect will be lesser, the image will be good enough. A simple lens never will produce razor edge-like image, but the Moon can be observed with a scope built with this objective lens. You can find cheap lenses with these attributes in old eye glasses; try 1 or 2 dioptries glasses - theirs focal lenght is 1000 and 500 mm. Never use plastic ones, the plastic is for ONLY eye glasses, believe me, its refracting errors are horrible over the focal lenght!

2. Hack the focal ratio: measure the focal lenght of a lens, and take its 1/10, and cut a blende with this inner diameter from not glossy, black cardboard, cover the original lens with it axially to get a smaller diameter with the same focal lenght, and you have a hached lens with 1/10 focal lenght. But remember that the smaller diameter can't gather as much light as the original; the ratio is a square, so when you reduced the diameter to 1/2, the light gathering ability of the hacked lens will be only 1/4 of it. This may be useful when looking at Moon, but the dim galaxies and nebulae won't be seen with a scope with an objectiv diameter under 70-80 mm.

3. Use achromats (well, this is not so easy, but no doubt, the best way.) For a good small scope for cheap is available <a href="">here</a> - this is a kit for children, I have built it in a school (as a classroom-activity leader teacher), and its imaging is very cool, but the joy of the DIY making is remains. In the pack you can find 3 achromatic lenses; one for the objective and two for an almost perfect ploessl-eyepiece, and some cardboard supports for it (I haven'n used it, anyway). Check it, if you want. To admire the Moon or Jupiter and Saturn this set may be perfect.

And never use lenses under 5-6 focal ratio, because those lenses are big challenge even for a high precision achromats, ar apochromats. Simple lenses are useful for astronomy with only these very limited ways.

Sorry, I was too long, I'm afraid. ;-)

sarvesh7 (author)BigCthulhu2015-04-13

That was really helpful bigcthulhu

sarvesh7 (author)2015-04-13

This I really nice and proper instructable and I am looking forward to make a telescope. Could you please tell me what should be the ratio of diameter of both lens?