Pin Hole Photography
This Finney slide bar pinhole/zone plate combines a pinhole and a zone plate.
A zone plate uses dark
rings to diffract light.
The Diana is a cheap plastic film camera favored by many artists.
It seems like we should end this chapter on a topic— pinhole photographywhere you replace the very expensive lens on your camera with a hole the size of a pin. Surprisingly, lenses are not actually needed to take a picture. You can even make a camera out of a shoebox with a small hole in one end and film in the other. Known as a pinhole camera, this primitive device can focus an image and record it on film. To make a photograph, the box is loaded in the dark with a light-sensitive film and the pinhole is covered with opaque tape. Peeling the tape back (much like a shutter) to uncover the pinhole (much like a lens aperture) begins the exposure, recovering the pinhole ends it. The exposed film is then removed in a darkroom and the image developed. In digital photography, the pinhole is placed in the body cap of a camera with a removable lens. The exposure is then made just like any other, except for a much longer exposure time. This is because pinholes have extremely small apertures—you'll find them at f/321 or so—and extremely great depth of field.
A variant of pinhole photography is zone plate photography. Light bends, or is diffracted, when it travels past an edge and the zone plate takes advantage of this principle. Instead of a pinhole, a zone plate is a transparent film with a clear central area surrounded by dark concentric rings. The size, number, and spacing of the rings depends on the focal length and aperture of the device. For this reason zone plates must be ordered in focal lengths that fit your camera.
Exposures with a zone plate are much shorter than with a pinhole, but the images are not as sharp. Some light goes straight through the film without being diffracted so highlights have a ghostly, romantic appearance, almost as if they have halos.
One step up from pinholes is the Loreo Lens in a Cap that turns your camera into a digital Diana. This simple device has a small fixed lens in the body cap so you can still take snapshots. The camera's autoexposure system won't work because the aperture is fixed, but you can adjust the shutter speed to control exposures. The len's fixed focus gives you a focal length of 35mm, and aperture range of f/5.6 to f/64 (selected by turning an aperture disc) and depth-of-field from 20 inches (5cm) to infinity. When taking close up photos you can clip on the Loreo Lubot for 10X magnification.