• Cell phone or electronic tablet
• Shoe box (for cell phone) or large cardboard box (for tablet)
• Magnifying lens or magnifying sheet Cutting tool
• Tape
• Box or table, to set up projector
• Flat white surface, for the screen

Safety tips and hints

• This project requires some cutting with sharp tools and may be better for older kids.

• A homemade projector will not produce high-definition images because hand-held devices don’t emit enough light, but this is a fun way for kids to learn a little science and watch videos.

Protocol

1. Turn the light setting and volume on your device all the way up.

2. Set your phone or tablet down against one end of the box, flush with the cardboard, and mark where the top of your device touches the box.

3. Line up the top of your magnifying lens or sheet with your mark on the box, trace it, and cut a hole slightly smaller than the size of your magnifier. Cut the opening so that when you place your device on the opposite side of the box, the center of your device will line up approximately with the center of your magnifier. You may have to remove the lens from the holder of a magnifying glass to center it.

4. Tape the lens into the hole you cut. If you are using a magnifying sheet, be sure that the grooved side faces in and the smooth side faces out.

5. Lock the portrait orientation on your phone, so the image can’t flip, and open a photo to focus on.

6. Test your projector when it’s dark outside or in a dark room. Turn the device upside down, placing it in the box on the side opposite the lens.

7. Set your projector on a box or table and focus your image on a flat white surface, such as a garage door, paper, or a sheet. You will have to play around with the distance between the projector and the screen, depending on the distance between the device and the lens and the magnification. To make the image larger, move the box away from the screen and move your device forward inside the box to get perfect focus. Remember to keep the device screen at a 90-degree angle with the bottom of the box.

8. When you have the focus set, start your movie, secure the device to the back of the box, close the lid, or cover the box with a towel to block out excess light, and enjoy the show!

The Science Behind the Fun

When light from your device passes through the lens on your projector, it slows and bends to form an identical upside-down image at a focal point on the other side of the lens. This light-warping property is called refraction.

Although light travels in a straight line from its source, it changes speed and bends when it passes through a new medium, such as a lens. The shape and thickness of a lens determines how and where it refocuses the light waves. Lenses are designed to bend light to focus images in a specific way. Eyeglasses, telescopes, and microscopes all use lenses to help us see things better.

It’s essential to adjust the distance between the device, the lens, and the projection surface to get the focal point just right. Since the lens flips the image, you have to keep the screen on your phone upside down to see the image right side up on the movie screen. The lenses in our eyes flip images too, but our brains correct for the difference, so we never even notice.

Creative Enrichment

1. Can you design a better projector? How does the size of the box affect the image?

2. What happens to the image if you add a second lens to your projector?

3. Can you make an even bigger, sharper image with a laptop that produces more light?

Liz Lee Heinecke is a molecular biologist, an author, a mother, and has spent her fair share of time teaching science to everyone from nursing students to her own three children.

Reprinted with permission from Outdoor Science Lab for Kids: 52 Family Friendly Experiments for the Yard, Garden, Playground, and Parks by Liz Lee Heinecke, published by Quarry Books, an imprint of Quarto Publishing Group, 2016. Photos by Amber Procaccini Photography.