How to Build a Pinhole Camera for Skywatching

So, you’ve been watching the news (or reading this blog) and have realized that the transit of Venus is tomorrow – a momentous astronomical event that once over won’t be back until 2117. So, how do you view it? Since you obviously can’t look directly at the sun, you’ll need someway to view the transit safely.

I’m serious about the whole don’t-look-at-the-sun thing. You can seriously damage your eyes even by a short look at the sun without protection. What happens if you look at the sun without protection? Imagine focusing sunlight through a magnifying glass onto a piece of paper. See that paper catch on fire? Well, that’s what’s happening to your unprotected eyes, except the glass is your eyes’ lenses and the paper is your retinas. Oh, and your retinas don’t have any pain receptors, so your eyes can be severely damaged before you know anything is wrong with them.

Isn’t nature fun?

So you’ll need another option. You could go out and buy specially prepared eclipse glasses, but if you don’t have access to those, you can whip up a handy pinhole camera out of household materials.

Here’s how a pinhole camera works. A darkened box has a pinhole at one end and a projection screen at the other. Light travels into the pinhole and projects itself onto the screen at the other end. By watching the projected image, you essentially get an upside-down mini-version of the scene outside – in this case, the transit.

I’m making this camera from scratch, but the design of it is largely based on the article “How to View an Eclipse” by Ron Hipschman.

To make your pinhole camera, you’ll need the following:

  • black Bristol board
  • duct tape
  • white paper
  • aluminum foil
  • pushpin
  • scissors and X-Acto knife

First, cut the black Bristol board into a triangular prism shape, which is composed of three rectangles with equilateral triangles on the ends. According to the above-mentioned article, the size of the resulting image is dependent upon the length of the prism and can be determined by multiplying the length of the prism by 0.0093 (or about 1/100). So, a 2 m-long prism will produce a 2 cm-sized image. My entire prism – unfolded – is 1 m long, and folds up to be about 86 cm, giving me a 8.6 mm image.

Then, fold all of the edges up to form a triangular prism, using the duct tape to seal the edges together.

At one of the triangular ends, attach a small triangle of aluminum foil. Then, poke a hole through the triangle with the pushpin.

On the side near the opposite end, cut a small square hole. This hole will be the viewing area.

Place a small triangle of white paper in the viewing end. This is the projection screen.

The pinhole camera is now complete.  All that’s left is to aim the pinhole end at the sun and view the resulting image through the viewing end. As it’s a cloudy day today, I can’t test this out, but tomorrow looks promising for viewing the transit. Pictures to come!

Transit image via Wikipedia provided by Benutzer:Klingon, licensed under the Creative Commons Attribution-ShareAlike 3.0 License.

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