Build a safe solar pinhole viewer

Posted by Michael Bakich
on Tuesday, September 02, 2014

OK, you want to view the Sun, but you don’t have an approved solar filter for your telescope. Maybe you don’t even have a telescope. No problem. I’ll bet you have a cardboard box. That and a few common supplies will let you build a pinhole viewer that you can observe the Sun with. And while I admit that the image you’ll see won’t rival that through a properly filtered telescope, it will be the Sun, and you can watch it as long as you want without any safety concerns.

Just follow the steps in the captions. Feel free to experiment with the size of the box, whether or not you leave the extra cardboard pieces attached, or the pin’s diameter. In fact, if you’re a clever soul, you may want to mount the box on a thin plywood base, which you then can attach to a sturdy camera tripod. That way, you won’t have to hold the box while viewing the Sun.

This activity is great for school classes. (I suggest the teacher cuts out the hole.) Please do leave any improvements you come up with in the “Comments” area.

Step 1: Start with a cardboard box at least 18 inches long. If you use a box shorter than this, the projected image of the Sun will be unacceptably small. // All photos: Michael E. Bakich

Step 2: On one of the box’s smaller ends, trace a circle by using a quarter.

Step 3: Carefully cut out the circle with a sharp knife.

Step 4: Note that the hole doesn’t have to be perfect — or even round!

Step 5: Cut out a piece of aluminum foil (I used a fairly thick variety) big enough to cover the hole in the box.

Step 6: Tape the foil over the hole.

Step 7: Poke a hole in the foil using a pin. A pin is better than most items you could use because you want a hole with clean (non ragged) edges. As a variation, you can try using a sharp pencil. That will produce a larger hole. Careful, though. If your hole is too big, you’ll lose the pinhole camera effect and you’ll just see an out-of-focus blob.

Step 8: Inspect the hole for roundness and make sure nothing is blocking it.

Step 9: Cut away as much of the extra cardboard pieces as you want. Alternatively, you could fold them over and tape them to the box’s sides, making the assembly a bit sturdier.

Step 10: Tape a white piece of paper on the inside of the box opposite the hole.

Step 11: Point the hole at the Sun and observe the projection on the paper. Congratulations!

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