Overview

The “camera obscura” is a dark box with a pinhole on one end and a screen on the other. The screen captures light reflecting off an object through the pinhole as an inverted image. We can see this inverted image by taking a picture of the screen via digital camera with a long exposure time.

Approach

We used a Canon EOS Rebel T3i with Tamron 18mm-270mm zoom lens and shot in manual mode with 30s exposure time, F8.0 aperture and ISO 3200. We calculated the pinhole sizes from 1.9 * sqrt(185mm*550nm) = 0.0191655mm where f = 185mm, giving us 0.02mm for the smallest pinhole size, but since it was technically difficult to make a hole that precise, we did 0.5mm instead. We created the three pinhole sizes of 0.5, 3 and 5mm on an index card, and taped over any remaining openings of the box.

On our first attempt, we used the wide side of the shoebox as the screen which we covered with white printer paper and used black electrical tape on all other sides of the interior. The focal length between the screen and the digital camera lense was too small, which made it hard for the Canon to focus.

On our second attempt, we used the longer side as the screen which we covered with white paper and used black electrical tape on all other sides of the interior. With a longer focal length, it was easier for the Canon to focus, which resulted in sharper images.

Analysis

The optimal pinhole size was 3mm because it resulted in the sharpest quality photos with medium lighting. The 0.5mm pinhole was too small and produced blurrier images due to diffraction. The 5mm pinhole let in the most light but was blurry as a result of points on the object hitting multiple areas on the screen.

Additional images (with 3mm pinhole)

"Stand there for 30 seconds"

David on the phone; Trees in front of Stanley Hall

Bells & Whistles

Light painting is a technique that involves long exposure times to capture light pointed at the camera. We used the flashlights on our phones and 30 second exposure time to capture these pictures on Memorial Glade.