DIY PVC Refracting Telescope for Stargazing

Gazing at the stars inspired me to build my own telescope for the Instructables Space Contest. As a student with a passion for space, I wanted a budget-friendly way to observe the Moon and planets. This simple refracting telescope uses two lenses and PVC pipes to bring the cosmos closer. With some basic materials and a little patience, you can create a functional telescope to explore the night sky. The design requires no complex tools and minimal cost – perfect for a student project that celebrates the wonders of space.

A refracting telescope works by using two convex lenses of different focal lengths to magnify distant objects. When the lenses are held a certain distance apart, they produce an upside-down magnified image of a faraway object. The distance between the objective (front) lens and the eyepiece lens should be about the sum of their focal lengths for a clear image. In this project, we’ll use a large lens to gather light and a small lens to magnify the image. By the end, you’ll have a DIY telescope that can reveal craters on the Moon and more – all built with your own two hands!

1. Convex lenses (2): One large objective lens (to collect light) and one smaller eyepiece lens (to magnify). For example, a 50 mm diameter magnifying glass lens (focal length ~300 mm) as the objective, and a smaller lens (focal length ~50 mm) as the eyepiece works well. This combination would give about 6× magnification (since magnification ≈ objective focal length ÷ eyepiece focal length. You can salvage these from old magnifying glasses or purchase them online.
2. PVC pipe: One length of PVC pipe to serve as the telescope tube. Choose a diameter that fits your objective lens. For a 50 mm lens, a PVC pipe with ~50 mm inner diameter works. The length of the pipe should be a bit shorter than the sum of your lenses’ focal lengths (we will fine-tune length during focusing).
3. PVC couplers/adapters:
4. An endcap or coupler for the front of the tube to hold the objective lens. The lens should fit snugly into it (friction fit or with tape). For instance, if using a 50 mm lens, a 50 mm PVC endcap or coupler can hold it in place.
5. (Optional) A smaller diameter PVC tube or adapter for the eyepiece. This can slide inside the main tube for focusing. For example, if the main tube is 50 mm, a 40 mm or 25 mm tube with a reducer can serve as an insert for the eyepiece.
6. Tape: Electrical tape or masking tape for securing lenses and preventing light leaks. Tape can also build up the diameter of an eyepiece holder for a snug fit.
7. Tools: A small saw or PVC cutter to cut pipe to length, sandpaper to smooth cuts, and a ruler or measuring tape. A marker is useful for marking cut points.
8. (Optional) Paint: Flat black paint for the inside of the tube (reduces internal reflections), and any color paint for the outside for a finished look. Spray paint designed for plastic works well.
9. (Optional) Tripod mount: If you have a camera tripod, a 1/4ʺ bolt and nuts can be used to attach the telescope to the tripod. This makes it easier to keep it steady when stargazing.
10. Safety gear: Sanding PVC can produce dust, so wear a mask and safety glasses when cutting or sanding.

Materials for building the PVC telescope, including PVC pipes, connectors, lenses, and tools. Having all parts ready helps to ensure a smooth build process. Notice the spray paint cans used to paint the tube and the tape for securing the lenses.

Understanding your lenses’ focal lengths is crucial before cutting the tube. The focal length is the distance from the lens to the point where it focuses light. Here’s how to find it:

1. Objective Lens: Take the larger lens and face it towards a distant scene or a bright light source (for example, point it at a distant tree or streetlight, or use sunlight projected onto a card – do NOT look at the Sun through the lens). Hold a sheet of white paper behind the lens and move it back and forth until the image comes into focus on the paper. Measure the distance from the lens to the paper when the image is sharp – that distance is the objective’s focal length. For a typical magnifying glass lens, this might be around 250–300 mm.
2. Eyepiece Lens: Repeat the process with the smaller lens. Its focal distance will be much shorter (perhaps 50 mm or so). Often, the eyepiece lens can be tested by bringing it close to a paper and focusing on a bright object or even a light bulb across the room. Measure the distance at clear focus.

If you don’t have a ruler handy, an alternative quick method is to pair the lenses and find the focus by trial. Hold the two lenses in line (objective in front, eyepiece near your eye) and look at a distant object. Adjust the distance between them until the distant object appears magnified and clear. You’ll find there’s a specific separation where the image is sharp – that gives you an approximate idea of how far apart the lenses need to be. Mark or note this distance.

With the focal lengths determined, it’s time to cut the PVC tube for the telescope’s body. The goal is to cut the tube so that when assembled, the distance between the two lenses is roughly the sum of their focal lengths for distant focus.

1. Calculate Tube Length: Add the focal length of the objective lens to that of the eyepiece lens. For example, if your objective is ~300 mm and eyepiece ~50 mm, the ideal separation is ~350 mm. Cut the main PVC tube a little shorter than this sum (about 10-20 mm shorter) to allow some room for focusing adjustments. It’s better to cut slightly short; you can extend the length using a sliding eyepiece tube or even by not fully inserting a coupler, whereas a tube cut too long might not focus at infinity without modification.
2. Mark and Cut: Use a measuring tape to mark the length on the PVC pipe. Ensure the end of the pipe is square; if not, you may want to trim a bit off first. Secure the pipe (or have a friend hold it) and cut at the marked line using a hacksaw or PVC cutter. Cut slowly and evenly to get a straight cut.
3. Smooth the Edges: After cutting, the edges of the PVC may be rough or have burrs. Use sandpaper to smooth the cut ends. This not only makes it safer to handle but also ensures the couplers and endcaps will fit nicely without obstruction. Wipe away any plastic dust before proceeding.

At this point, do a test-fit: hold your two lenses at either end of the cut tube (without securing them yet) and see if you can roughly focus on a distant object. If the image is nearly focused or just slightly off, your tube length is good. Minor focusing differences will be adjusted in the next steps. If it’s very blurry and you can’t find focus at all, you may need to adjust the tube length (for instance, cut it a bit shorter if too long).

The objective lens is the large lens at the front of the telescope that gathers light from distant objects. Mounting it securely and evenly is important for clear viewing. Here are a couple of ways to mount the objective:

1. Using a PVC Endcap or Coupler: If you have an endcap or a coupler that fits your PVC pipe, see if the objective lens can sit inside it. Many PVC endcaps have a lip or ridge inside – your lens can rest against this ridge. You might need to secure it with a bit of tape around the edges or a thin bead of glue to keep it from rattling. In our build, the lens sat snugly in a 50 mm coupler without glue – a friction fit held it in place. If it’s loose, wrap the circumference of the lens with electrical tape until it fits tightly in the cap or coupler. Ensure the lens is flush and parallel to the cap’s opening (not tilted). This will be attached to the front end of the main tube.
2. Tape Method (if no cap): If you don’t have a suitable cap/coupler, you can directly tape the lens to the end of the PVC tube. Center the lens over the opening and use strips of tape to secure it around the edges. Make sure there are no gaps where light can leak in around the lens – overlap tape as needed to seal the edge. It’s a rough method, but it can work in a pinch. Just be cautious not to get tape onto the clear part of the lens.

Before finalizing, double-check that the concave side/convex side orientation of the lens is correct if your lens has one side more curved. Generally, you want the more curved side facing outward for an objective lens, but for a simple magnifying glass lens it likely doesn’t matter much. The key is that the lens should face the eyepiece with the same orientation you used when determining focal length (if you noticed a difference).

Once the objective lens is mounted in the cap or coupler, attach that piece to the PVC tube. PVC couplers usually just slide on; push it firmly onto the tube end. If using an endcap, it might be a tight hammer-fit. Now your front lens is in place.

Light-blocking Tip: It’s important that only light coming through the lens enters the tube. If there are any gaps or transparent areas around the lens mount, line them with black tape or paint to prevent stray light which can reduce contrast. Many telescope makers paint the interior of the tube flat black to absorb stray light. You can do this now by spraying the inside of the tube with flat black paint and letting it dry (be careful to mask the lens itself from paint). This will improve image quality.

The eyepiece is the small lens you will look through. It needs to be held at the proper distance from the objective lens inside the back end of the tube. You have a few options for mounting the eyepiece:

1. PVC Reducer/Adapter: A convenient method is to use a PVC reducer that steps the main tube diameter down to a smaller size. For example, a 50 mm to 25 mm reducer could hold a small lens of around 25 mm diameter. If your eyepiece lens fits into a smaller PVC fitting, place it there. You might use a short piece of smaller pipe as an eyepiece holder. Insert the eyepiece lens into one end of that small pipe (tape or glue it in place if needed), and then insert this small pipe into the reducer or directly into the main tube. You can wrap tape around the small pipe to achieve a snug, sliding fit in the main tube. This effectively creates a focusing draw-tube.
2. Direct Mount or Tape: If you don’t have a secondary tube, you can tape the eyepiece lens into the back end of the main tube similarly to the objective. However, it’s a bit trickier because you might need to adjust its position for focus. One approach is to cut a short segment of the same PVC pipe (or a slightly smaller diameter pipe) and tape the eyepiece lens onto the end of that segment, creating a makeshift eyepiece module. This module can then be slid in and out of the main tube as you find the correct focus, and then secured with tape once in the right spot.

Make sure the eyepiece lens is oriented correctly (if it has a more curved side, typically the more curved side faces your eye for an eyepiece). Also ensure it’s clean – no fingerprints or dust, since you’ll be looking through this lens at a very close distance.

At this stage, you essentially have both lenses mounted on either end of the tube. The objective lens is fixed at the front, and the eyepiece lens is at the back where you will put your eye. The rough focusing should be close if your tube length was cut well, but now we fine-tune that.

Assembling the eyepiece end of the telescope. A smaller PVC tube or adapter can hold the eyepiece lens and slide within the main tube for focusing. Wrapping tape around the smaller tube helps achieve a snug fit. Ensure the eyepiece is aligned straight with the objective lens for a clear view.

Unlike a store-bought telescope, our DIY PVC telescope doesn’t have a fancy focusing knob (unless you engineered one). We will focus it manually by adjusting the distance between the lenses slightly:

1. Initial Test: Point the telescope at a distant object (for example, a tree or streetlight down the street, or the Moon at night). Look through the eyepiece lens at the back. If the image is blurry, slowly slide the eyepiece closer or farther from the objective by moving that small eyepiece tube (or by slightly withdrawing the coupler holding the eyepiece, if you used that method). There should be a position where the image becomes sharp.
2. Fine Adjustment: It might help to do this in daylight on a distant object first to get roughly focused, then check on a star or the Moon. If your design uses friction (tape) to hold the eyepiece tube, you can adjust and then secure the position with an extra wrap of tape once the focus is correct for distant stars (infinite focus). Remember that different viewers (or looking at closer objects vs. stars) might require slight re-focusing. It’s okay to mark the tube at the ideal focus position for infinity.
3. Secure the Eyepiece: Once you find a good focus for distant objects, lock it in. This could be as simple as adding more tape so the eyepiece tube doesn’t slide easily, or tightening a screw if you added one as a clamp. Don’t make it permanent – you might want to refocus later for another user or if you swap eyepieces.

Now, test the telescope on the night sky! Point it at the Moon first – it’s the easiest target. You should be able to see some of the larger craters and seas on the Moon’s surface. The image will likely be upside down (rotated 180°) – that is normal for a simple refractor telescope without a prism. For stargazing, orientation doesn’t really matter, but keep this in mind if you use it for terrestrial viewing. If the Moon looks clear, try Jupiter or Saturn (they will appear as bright dots – you might glimpse Jupiter’s moons as tiny specks if your magnification is sufficient). Stars will always appear as points of light (even in large telescopes, they don’t magnify into disks).

Your DIY telescope is now functional, but a few finishing touches can improve its usability and longevity:

1. Secure and Seal: Check all connections – if any piece is wobbly, add tape or a set screw to tighten it. Ensure the lenses are secure; you don’t want the objective lens falling out during use! If you hadn’t already, consider using a bit of glue or silicone sealant to fix the objective lens in place permanently (just a few small dabs so you can remove it later if needed). The eyepiece can remain adjustable.
2. Aesthetics and Protection: If you have spray paint, give the outside of the tube a coat of paint. A flat black or white are common telescope colors (white helps reduce heating in sun, black looks classic and helps hide it in the dark). Painting not only makes it look great but also protects the PVC from UV damage if you use it in sunlight. Be sure to cover the lenses while painting to avoid overspray.
3. Tripod Mount (Optional): Hand-holding a telescope, especially at night, can be shaky. If you can attach it to a tripod, you’ll get a steadier view. One simple way is to use a pipe clamp or zip-ties to strap the telescope to a camera tripod’s quick-release plate. A more elegant way is drilling a small hole in the PVC (near the bottom, where it won’t interfere with the light path) and epoxying a 1/4ʺ nut inside. Then a tripod screw can attach to that nut. This turns your PVC telescope into a pseudo-spotting scope that can mount on any standard tripod.
4. Using the Telescope: To use, find a stable spot outdoors away from bright lights. Allow your eyes to adjust to the dark. Aim the telescope by sighting along the tube (you can attach a simple pointer or just use the tube’s shadow in daylight). Center the Moon or a star in the view. It helps to use low magnification (longer focal length eyepiece) to find targets, as they will have a wider field of view, then you can swap in a higher magnification eyepiece if you have one. Since this DIY scope likely has a fixed eyepiece, it’s roughly a low-to-medium power scope. Enjoy the crisp view of the Moon’s details or sweeping star fields through your handmade telescope!

Building this PVC refracting telescope was an enriching experience. Not only did I recycle simple materials to create a working scientific instrument, but I also deepened my understanding of how telescopes work. Using two lenses to magnify distant objects demonstrates basic optical principles: the objective lens gathers and focuses light, while the eyepiece lens magnifies that focused image. This DIY telescope may be simple, but it opens a window to observe craters on the Moon, the phases of Venus, or the Galilean moons of Jupiter – inspiring any student astronomer to gaze a little deeper into space.

Through this project, I learned to troubleshoot and adjust an optical system, much like early astronomers did with their first telescopes. It’s incredibly rewarding to point your homemade device at the night sky and see something with your own eyes that’s normally invisible. I hope this instructable empowers you to build your own telescope and join in the stargazing adventure. The universe is now within your reach – happy observing!