A pinhole camera is a simple camera without a lens but with a tiny aperture, effectively a light-proof box with a small hole in one side. Light from a scene passes through the aperture and projects an inverted image on the opposite side of the box. The pinhole in a pinhole camera acts as the lens, forcing every point emitting light in the scene to form a small point on the film, resulting in a crisp image. The pinhole camera works on the principle of rectilinear propagation of light, where each point on the surface of an illuminated object reflects rays of light in all directions. The hole lets through a certain number of these rays, which continue on their course until they meet the projection plane where they produce a reverse image of the object.
Pinhole cameras can be handmade by the photographer for a particular purpose. In its simplest form, the photographic pinhole camera can consist of a light-tight box with a pinhole in one end, and a piece of film or photographic paper wedged or taped into the other end. A flap of cardboard with a tape hinge can be used as a shutter. The pinhole may be punched or drilled using a sewing needle or small diameter bit through a piece of tinfoil or thin aluminum or brass sheet. Pinhole cameras can be constructed with a sliding film holder or back so the distance between the film and the pinhole can be adjusted. This allows the angle of view of the camera to be changed and also the effective f-stop ratio of the camera. Moving the film closer to the pinhole will result in a wide-angle field of view and shorter exposure time. Moving the film farther away from the pinhole will result in a telephoto or narrow-angle.
Pinhole cameras have some limitations, such as long exposure times, resulting in motion blur around moving objects and the absence of objects that moved too fast. However, other special features can be built into pinhole cameras, such as the ability to take double images by using multiple pinholes or the ability to take pictures in cylindrical or spherical perspective by curving the film plane.
In summary, a pinhole camera is a simple camera without a lens but with a tiny aperture that projects an inverted image on the opposite side of the box. It works on the principle of rectilinear propagation of light and can be handmade by the photographer for a particular purpose. Pinhole cameras have some limitations, but other special features can be built into them.
