This is part 3 of a 6 part series on getting to know your digital camera. Read part 2: What the Camera Makers Assume You Already Know.

The pinhole camera is proof that fundamental principles do not change. Euclid demonstrated the image-forming possibilities of the pinhole in 300 B.C. In the 16th century, Leonardo da Vinci is credited with giving a description of the pinhole camera more or less as we think of it today.To make photographs, you need nothing more than a light-tight box with a pinhole opening!

Pinhole Camera

A Pinhole Camera consists of a small aperture that light passes through, a dark enclosure, and a piece of film. As shown in the diagram below, an object placed in front of a Pinhole Camera forms a clear image on the film without the need for a lens. A lens would be used in place of the pinhole to collect light and focus it on the film. (ref: Camera Optics)

Imagine the opening with a moveable cover over it. We’ll call the opening the “aperture” and the moveable cover the “shutter.” (It?s all about terminology). Now let’s say you have a piece of photographic film inside the box, opposite the pinhole. When you uncover the opening, light enters the box, changing (exposing) the film, in such a way as it captures the variably lit image projected from the outside world. Photographic film is sensitive to light. You expose it to light in a controlled fashion, process the film with certain chemicals, and you end up with a “negative,” from which the photofinishing lab makes a paper print. A digital camera works much the same way, only it uses a digital image sensor instead of photographic film.

In the pinhole camera, you uncover the pinhole for a moment to allow light to expose the film. There are only two main variables controlling exposure:

1. Amount of time the pinhole is open and
2. The size, or diameter of the opening

In other words, exposure is determined by how much light hits the film. The wider the opening, the more light gets in during the same exposure time.

A theoretical ideal exposure requires proper combination of the size of the hole and the time the pinhole is open. Or, in camera lingo, proper combination of aperture and shutter speed. In the “auto” mode, a camera will attempt to determine the proper exposure and adjust aperture and shutter speed by itself.