Pinhole cameras are the one of the simplest and oldest types of cameras. In a pinhole camera, light passes through a light-proof container through a tiny hole. The light streams through the box and projects an image on the back of the box's interior, to which a piece of film has been affixed. An image then develops on the face of the film much in the same way that it does in a typical 35mm film camera. It is possible to purchase pinhole cameras, but most users choose to make their own. Pinhole cameras can easily be made from common household objects. Due in part to their low cost and ease of use, the creation and use of pinhole cameras is often taught in elementary photography courses.
Pinhole cameras can be made from a variety of air-tight containers, such as paint cans, juice boxes, or oatmeal canisters, which are operated by simply exposing the hole and later covering it with an index card or piece of dark material that acts as a shutter.
Because pinhole cameras have no focusing apparatus, the size, shape and distance of the hole from the film are important. Smaller holes will result in sharper images, and larger holes will create more diffuse images. However, the size of the hole also determines the amount of light exposure necessary to develop the image: smaller holes will require longer exposures, and larger ones will require shorter exposures.
In order to determine the proper diameter of the hole, the distance from the hole to the film at the back of the camera must first be measured. This distance is called the focal length. A mathematical formula can then be used to determine the size of the hole. One common formula used states that the diameter of the hole (d) = 0.0073 multiplied by the square root of the focal length (f). However, many photographers develop their own nuanced formulas and choose to experiment with different sizes and their resultant effects. There are also many online and print resources that can help beginners calculate the diameter of the hole.
Whereas most modern film cameras have an exposure time of a fraction of a second, the exposure time for pinhole cameras is much longer by comparison and can range from a few seconds to a few hours depending on the desired effect. Exposing the hole for a few seconds will produce a still image if the scene was posed and none of the objects in the field moved. However, allowing the hole to remain open while fixed on an a room full of moving people or a freeway with moving cars on it produces a time-lapse photograph, in which moving images are blurred and still images are sharp and focused.