You can build a working projector from a smartphone, a lens, and a light source
A homemade projector works by taking light from a bright source, passing it through or reflecting it off a smartphone screen or image, and focusing that light through a lens onto a wall or screen. The simplest versions use a smartphone as the light source and image, a magnifying glass or fresnel lens to focus the light, and a dark box to contain the light path. You will not get cinema-quality brightness or sharpness, but a basic projector can display a usable image in a dark room for under $50 if you already own a smartphone.
The core principle is the same as a commercial projector: light passes through a small, bright image and a lens magnifies and focuses that light onto a larger surface. The main trade-off in a homemade version is brightness and image quality. A smartphone screen is not as bright as a dedicated projector lamp, and a straightforward lens will not focus as sharply as a multi-element lens system. But for casual use — watching videos in a dark room, displaying photos, or running a presentation — a homemade projector can work.
Key Takeaways
- The simplest homemade projector uses a smartphone, a magnifying glass or fresnel lens, and a cardboard box or tube to hold the components in alignment.
- Brightness depends on your smartphone's screen brightness and the darkness of the room; homemade projectors work best in near-total darkness.
- Image quality improves when you use a larger-diameter lens and position it at the correct distance from the smartphone screen.
- You can build a working version in under an hour using materials from a hardware store and items you may already have at home.
The smartphone-and-lens method: the easiest build
Start with a smartphone, a magnifying glass or fresnel lens (a thin, flat lens with concentric rings), and a cardboard box or PVC pipe. A fresnel lens is preferable because it is thinner and lighter than a magnifying glass, and you can find them online for $10 to $20. Mount the smartphone inside the box so its screen faces the lens, then position the lens at a distance from the screen where the image comes into focus on the wall behind it. The distance depends on the lens focal length — usually between 4 and 12 inches for a typical magnifying glass.
Cut a hole in the box large enough for the lens to fit through, and seal the rest of the box with black tape or paint to block stray light. Angle the smartphone screen upward slightly so the projected image lands on a wall or screen at a comfortable viewing height. You will need to invert the image on your phone (most phones have a screen rotation lock; disable it and rotate the phone 180 degrees, or use an app that flips the display) because a lens inverts the image as it projects it.
The image will be dim, so use your phone's maximum brightness setting and darken the room as much as possible. Close curtains, turn off overhead lights, and let your eyes adjust for a few minutes. In a very dark room, the image becomes visible enough to watch video or view photos.
Building a box projector for better stability
A cardboard box projector is more stable than a handheld setup and easier to aim. Use a sturdy cardboard box roughly 12 inches long and 8 inches wide — a shoe box or small storage box works well. Cut a hole in one end of the box for the lens, and drill or cut a smaller hole in the opposite end for the smartphone camera (you will not use the camera, but the hole lets you see inside to position the phone). Mount the smartphone inside using a small stand or by taping it to the inside of the box, with the screen facing the lens.
Paint the inside of the box flat black or line it with black paper to absorb light and reduce glare. Position the lens in its hole so it sits about 1 to 2 inches in front of the smartphone screen. You may need to move the lens closer or farther away to focus the image — this is called the focal distance, and it varies by lens. Once you find the right distance, find the lens in place with a cardboard ring or a 3D-printed lens holder.
Prop the box on a small stand or stack of books so the projected image lands on a wall or screen at eye level. Angle the box slightly if needed. The image will be upside down and reversed left-to-right, so flip your phone's display before you start.
Using a tube projector for a compact design
A PVC pipe or paper tube projector is lighter and more portable than a box. Use a PVC pipe 3 to 4 inches in diameter and 12 to 18 inches long, or a cardboard mailing tube of similar size. Drill a hole in one end for the lens and mount the lens in a 3D-printed or cardboard ring that fits snugly inside the tube. find the smartphone at the other end of the tube using a small stand or by taping it to a piece of cardboard that slides into the tube.
Paint the inside of the tube black to reduce reflections. Slide the smartphone holder into the tube until the image focuses on the wall, then lock it in place with a set screw or by wrapping tape around the holder. A tube projector is easier to aim and adjust than a box because you can slide the phone holder in and out to change focus without disassembling anything.
Choosing the right lens for your projector
The lens is the most important component. A larger lens diameter and a shorter focal length produce a brighter, wider image. A magnifying glass typically has a focal length of 4 to 8 inches and a diameter of 2 to 4 inches. A fresnel lens can have a focal length of 4 to 12 inches and a diameter of up to 8 inches or more. Larger fresnel lenses are available online and cost $15 to $40.
Focal length determines how far the lens must be from the smartphone screen to focus the image. A shorter focal length means the lens sits closer to the phone, which makes the projector more compact but produces a smaller image on the wall. A longer focal length means the lens sits farther away, which produces a larger image but requires a longer box or tube. For a typical living room, a focal length of 6 to 10 inches is a good balance.
Test the lens before you build the projector. Hold it in front of your smartphone screen in a dark room and move it closer and farther away until the image on the wall comes into sharp focus. Measure the distance from the lens to the screen — that is your focal length for that lens and phone combination.
Improving brightness and image quality
Brightness is the biggest limitation of a homemade projector. Your smartphone screen can only emit so much light, and the lens cannot amplify light — it only focuses it. To improve brightness, set your phone to maximum brightness, use a phone with an OLED screen (which is typically brighter than LCD), and darken the room as much as possible. Close all curtains, turn off all lights, and wait for your eyes to adjust.
Image quality improves when the lens is clean, the smartphone screen is clean, and the image is in sharp focus. Wipe both the lens and the phone screen with a soft, dry cloth before you project. If the image is blurry, move the lens slightly closer or farther from the screen until it sharpens. A larger lens diameter also improves sharpness and brightness, so if you have the space, use the largest lens you can fit.
The distance from the lens to the wall also affects image size and brightness. Moving the projector closer to the wall makes the image smaller and brighter; moving it farther away makes the image larger and dimmer. For a 10-foot viewing distance, expect an image roughly 3 to 5 feet wide, depending on your lens and phone.
What to expect from a homemade projector
A homemade projector will not match a commercial projector in brightness, color accuracy, or sharpness. The image will be noticeably dimmer, especially if the room is not completely dark. Colors may look washed out because the smartphone screen is not as bright as a projector lamp. The image edges may be slightly blurry, especially if you use a straightforward magnifying glass instead of a quality lens.
But for casual use in a dark room — watching a movie with friends, displaying family photos, or giving a presentation to a small group — a homemade projector is functional and surprisingly effective. Many people report that a well-built projector can display a clear, watchable image 4 to 6 feet wide in a dark room. The experience is closer to an old-fashioned slide projector than a modern cinema projector, but it works.
Frequently Asked Questions
Can I use any smartphone with a homemade projector?
Yes, any smartphone with a bright screen will work. OLED screens are brighter than LCD screens, so newer phones tend to project better than older ones. Larger screens (6 inches or more) project larger images. The phone's processing power does not matter — only the screen brightness and size.
How bright will the projected image be?
Much dimmer than a commercial projector. In a very dark room, the image is visible and watchable, but you will not be able to use it in a lit room or outdoors. Expect to close all curtains and turn off all lights for the best results. The image brightness also depends on your lens size and the phone's maximum brightness setting.
What if the image is blurry?
Move the lens closer to or farther from the smartphone screen until the image sharpens. The correct distance is called the focal distance, and it varies by lens. Once you find it, mark or lock the lens in place. If the image is still blurry, try cleaning the lens and phone screen, or use a larger-diameter lens.
Can I project video or just still images?
You can project video, photos, presentations, or anything else on your phone screen. Just remember to invert the display (rotate the phone 180 degrees or use a display-flip app) because the lens flips the image as it projects it. Video playback works fine as long as the room is dark enough to see the image.
How much does it cost to build a homemade projector?
If you already own a smartphone and have a cardboard box at home, you can build a basic projector for $10 to $20 by buying a fresnel lens online. A higher-quality build with a larger lens and a PVC tube might cost $30 to $50. This is much cheaper than a commercial projector, which typically costs $200 to $1,000 or more.