ELI ON EARTH: Pinhole Cameras Could Make Viewing Solar Eclipse Easier and Safer for East Lansing Residents

Last week, ELi on Earth (EOE) focused on the when, where, and why of the coming partial solar eclipse, and this week, EOE looks at two ways to safely and cheaply view this week’s eclipse.

To review: This Thursday (October 23), a partial solar eclipse will visible in East Lansing from 5:37 pm until sunset at 6:42 pm, cloud cover permitting. A partial solar eclipse occurs when the moon partially blocks the sun. A total solar eclipse happens when the sun is completely blocked by the moon. The difference between a partial and total solar eclipse is important: only when the sun is completely covered by the moon is it safe to view an eclipse with the naked eye. If the sun is not completely covered, you should follow your mother’s advice and not look directly at the sun. (That means that this Thursday you should not look directly at the sun.)

Safe ways to view a partial eclipse include looking through a welder’s glass or welder’s helmet, using a camera with a special sun filter, using a sun telescope, and using a pinhole camera. Here we explain how to construct a sun telescope and a pinhole camera.

First, let’s look at how to build a solar telescope from a pair of binoculars. (You are NOT going to look through the binoculars at the sun!) In the picture shown above, taken at the Hannah Community Center, an area man and his son used binoculars plus an old chemistry stand and clamps to make a sun telescope in order to view the transit of Venus across the sun on June 5, 2012. (A detailed close-up is shown below. The boy is helping to shade the system to improve visiblity of the projection.) The design for this kind of sun telescope is straightforward:

1. Not looking at the sun, focus the binoculars on a distant object.
2. Then, using tape or clamps, mount the binoculars to a stick or small board so one lens can point to the sun while the eyepiece can be pointed to a white piece of paper or poster board. You are only going to use one side (left or right) of the binoculars, so it doesn’t matter if the binoculars are positioned upside down or sideways. The sun will move during the eclipse, so it helps to have a system you can easily adjust to track the sun.
3. Line up a clean, white sheet of paper or a white poster board behind the eyepiece. The light from the eyepiece should hit the paper. This will allow you to see the image of the sun, including the eclipse, as it is projected on the paper. Looking at the eclipse as it is projected on the paper is safe. (Again, looking directly at the eclipse with your eyes is not safe.) The binoculars should still be focused from Step 1, but you can turn the eye piece or the focusing dial of the binoculars to sharpen the image if needed.

The light of the sun is so bright that you will be able to see the image of the solar eclipse on the paper even outside without any other equipment. You can see more detail of the sun if you make the viewing area dark (darkening everything except for the light from the binoculars, perhaps by huddling under a dark blanket). Galileo set up his sun telescope so that the light came into a dark room and shone onto a white wall. The telescope Galileo used to discover sunspots was no better than a modern, inexpensive pair of binoculars.

A cheaper and easier way to see the progress of the partial eclipse is to use a simple pinhole. To build this system, you will only need two pieces of paper and a pin.

1. Choose your paper. You don’t have to be picky; two white unlined index cards work well enough. One piece is going to have the pinhole and the other will be the “screen.” It really does not matter what paper you pick, although a white, thicker piece of paper will work best for your screen and thinner paper is better for the pinhole.
2. Put a pinhole near the middle of one piece of paper. The cleaner and smaller the hole, the more focused the image of the partial eclipse will be.
3. Hold the papers so the sun shines through the pinhole and hits the “screen.” You can move the pinhole closer to the “screen” to make the image brighter (and smaller) and move the pinhole farther from the screen to make the image larger (and dimmer).

This pinhole viewer system is a known as a “pinhole camera.” (“Camera” refers to a device that captures an image, whether or not it projects the image onto a film.) Usually a pinhole camera is used in conjunction with a darkened viewing area because otherwise there is too much surrounding light to see the image. But for a solar eclipse, the shadow from the pinhole paper is dark enough that the image of the eclipse from the pinhole will be visible just fine.

There is a very nice description of how to make a classic pinhole camera at the San Francisco Exploratorium site.

If you are observant and lucky, on Thursday you will notice some natural pinhole cameras around you in East Lansing during the partial eclipse. For example, during a partial eclipse, the dappled light coming through a leafed-out tree and reaching the ground will change to show the crescents of the partially obscured sun of the eclipse. You may see hundreds of projections of the eclipse in the shadow of a leafy tree. Double pane windows may also create images of the eclipse.

These natural pinhole cameras exist around us all the time, but we don’t usually notice them because (1) the sun is round and typically unobscured, and so the sun’s light fills the entire “pinhole” making the image the same shape as the hole, and (2) the ambient light is so bright we can’t see the pinhole image. The image is still there, but our eyes and cameras are not sensitive enough to see it.

If you try either of these approaches and get some good photos in East Lansing, send them to ELi and we will be happy to publish them.

ELi provides a unique mix of high-quality, community-based, nonpartisan, factual, opinion-free reporting about East Lansing that you won’t find anywhere else! But it depends on tax-deductible reader donations to function! If you believe in ELi's mission of providing editorial-free high-quality news of the people, by the people, and for the people of East Lansing, donate easily online to support us. You can also donate by check. Thank you in joining your neighbors in supporting ELi as a critical resource for the people of East Lansing!