What Is a Camera? Building a Pinhole Camera to Find Out

This instructables project is my submission of Lab 1 of ECE516: Intelligent Image Processing at the University of Toronto taught by Professor Steve Mann (from MIT and UofT). It asks a fundamental question: What is a camera? I shall answer this question by building the simplest version of a camera: A pin-hole camera. I shall make a large pinhole camera, a small pinhole camera, and a practical camera with a lens. Using the Metavision™ principle, I will also be able to view what the pinhole camera is seeing and share with you my observations about how cameras function.

The pinhole camera is based on the camera obscura principle, where an inverted and reversed image of the surroundings is projected onto a surface through a small hole (the pinhole). This concept is considered an early predecessor of modern photography. In a pinhole camera, light from an object is reflected and focused onto a surface through the pinhole, creating an image of the object. In modern cameras, a lens is used for focusing, whereas in a pinhole camera, the pinhole serves this purpose.

Why do we see an upside down image in a pin-hole camera?

The rectilinear propagation of light refers to the straight-line movement of light rays in a vacuum. In a pinhole camera, light travels in straight lines from the objects in the scene and passes through the small pinhole, creating an image on the opposite wall. The light rays passing through the pinhole are bent (refracted) slightly, but the bending is negligible because the pinhole is so small. Ensuring the box being used to make the pin-hole camera is completely black/dark can greatly reduce the chance for light to be reflected as well.

Because the light rays are essentially unaffected by the pinhole, they maintain their straight trajectory, creating an image on the opposite wall that is upside down and reversed from left to right. The image is inverted because the light passes through the pinhole and projects an image from the opposite side, and the image is reversed because the light enters the camera from the front and projects an image on the back.

So, the rectilinear propagation of light explains how pinhole cameras work by demonstrating that light travels in straight lines and can be used to form an inverted and reversed image of a scene on a surface through a small aperture.

What is the optimal aperture size to use?

The optimal diameter of the aperture in a pinhole camera can be expressed as:

d = c * √(f * λ)

Where d is the optimal diameter of the pinhole, f is the focal length (distance from the pinhole to the image plane), λ is the wavelength of light, and c is a constant related to the Rayleigh criterion, with a typical range of values from 1.56 to 2. This formula takes into account the wavelength of light (approximately 500 nm), the distance from the pinhole to the image plane, and other factors, to determine the optimal size of the pinhole for a given set of conditions.

Calculation: d = c * √(f * λ) = 1.56 x sqrt(0.305 m * 550 nm) = 6.389*10^-4 = 0.025''

I selected a range of drill hole sizes to construct several apertures.

A note on safety from the lab manual: Make sure you keep the lens covered if it has no f-stop "C" (closed) setting on it. Don't leave lenses laying around where light might shine in and burn things, etc..

Is it better to have a large camera, i.e. does large-format pinhole photography produce better pictures, and if so, why?

There is a tradeoff between resolution and build-quality. Larger pinholes are easier to build, photograph with, let more light in, and in practice often produce better results but it suffers from slightly blurry images. Smaller pinholes are more difficult to build precisely, harder to photograph with (at least with my large phone), let less light in, but have higher resolution images.

Personally, the portability of a smaller pinhole camera makes it more appealing. I am willing to make the appropriate tradeoff in order to enjoy this convenience.

If you want to see other interesting pictures: https://docs.google.com/presentation/d/1aJi-JHAVE5wJFiMoBDbz7vdeVkc3zSzFmd13gyFpinU/edit?usp=sharing