Bottom: A pinhole blocks most of the light, allowing only single rays that form a dim image. Middle: A lens focuses light to form an inverted image. Schematic of image formation, showing rays of light from a stick figure. Where modern imaging systems like my fancy camera lenses rely on wave refraction to bend light and make an image, the pinhole camera forms an image simply by restricting the passage of light. The principle of the pinhole camera has been known for a long, long time, and is remarkably simple. The essential property of a visible image is that light at one point on the place where you're projecting the image comes from one and only one point on the surface of the image. To understand why this works you need to think about what it means to make an image of some thing. So, you don't need fancy glasses, just a box you can poke some holes in. The pinhole camera image is fainter, but shows about as much detail of the trees that are partially obscuring the sun as the eclipse glasses do. I haven't even done anything to change the scaling, here- these images are cropped only, not re-scaled. The top image there is from the pinhole camera, shot with my DSLR and a 50mm prime lens, and the bottom image is from the same camera looking toward the sun, with a pair of eclipse glasses held over the lens. blocked by leaves, shot through eclipse glasses.

Top: Pinhole camera image of the Sun partially blocked by leaves. Point the pinhole toward the Sun, look through the eye hole, and you'll see an image that's about as good as what you'll see through those expensive eclipse glasses: I have it mounted on a tripod, but that's overkill- you could perfectly well hold it in your hand. A little duct tape to seal up the edges of the box, and it's a perfectly good pinhole camera, projecting an image of the outside world on the white paper at the far end. There's a square hole cut in the end so you can look inside, and a tiny pinhole (made with the widget that came with my smartphone for popping out the SIM card, but you could use an actual pin, or a small paperclip) in the same end, inside the square of masking tape (which serves no purpose other than marking the approximate position of the hole. This is the solar imaging system I knocked together this weekend, consisting of a big shoebox (from a pair of size 13 basketball sneakers) with a white piece of paper taped to the inside (not shown). Pinhole camera system at Chateau Steelypips.

How to see the eclipse without goggles