Long Exposure Pinholes

This week our students built a simple pinhole camera to track the sun’s movement across the sky, and to observe how the sun’s path increases in height across the sky increases from the winter solstice to the summer solstice. As the sun rotates around the Earth, from winter to the summer, the angle of the sun goes from low to high. As a result, the sun traces higher and higher paths across the sun, reaching its maximum height at the Summer Solstice.

The image below shows the suns path from March 12th to May 20th. Gaps between the solar bands are caused by cloudy days, and gaps within a single band are caused by clouds passing over the sun.

To make the images, a piece of photographic paper is placed into a soda can that has a pinhole in it. The light from the sun exposes the paper and the path of the sun is recorded. The can is left outside for 1-2 months. After two months, it is taken inside and and the paper is scanned. The interesting fact about this type of image is that it is not developed. When its taken out, it is still light sensitive, so it has to be quickly scanned before the image degrades.

Building the Solar Pinhole Cameras

To build the camera, each student had to cut an aluminum can in half. Next, the used a hole punch to make a large hole in the side of the can. Then, they painted the inside of the can gray or black to reduce reflections, and painted the outside of the can gray. They used a needle to put a small hole in a piece of copper flashing and the hole was taped over the larger hole in the can. The photographic paper was loaded in the darkroom, and the can was closed using electrical tape and duct tape. Then, an identification label was placed onto the can. Finally the cans were collected and placed around the school facing the sun. They will be left outside until May 20th. The slide show below displays images of our students constructing the cans.

Update May 23rd: The slide show below displays a number of our students long exposure pinhole images. For each pair of images, the first image is the paper as it looks when it is taken out of the can and the second image is the paper scanned and inverted. Next year, we plan on having our students construct a wedge so that the entire path of the sun across the sky is visible. That is something we did not consider when placing the cans outside.