pinhole

A pinhole is a small, circular opening that allows light to pass through while blocking larger passages. In optics and imaging, a pinhole can serve as a simple aperture in place of a lens, most commonly used in a pinhole camera to form an image.

The image in a pinhole camera is produced by light traveling in straight lines from the scene through the hole and projecting onto a surface inside the enclosure. Because there is no lens, the resulting image is typically sharp over a wide depth of field and is inherently inverted. A very small pinhole reduces blurring from edges but also limits light, yielding dim images and longer exposure times. A larger hole increases brightness but can soften detail. The hole’s diameter and the distance from the hole to the recording surface (the focal length) together determine magnification and sharpness; this trade-off between brightness and clarity is a central consideration in pinhole photography.

Pinhole photography is valued for its unique, soft aesthetic and for its educational simplicity. DIY pinhole cameras are often built from simple boxes, cans, or existing cameras with their lenses removed. The technique is used in art, experimental photography, and teaching about optical projection, geometry, and exposure.

Beyond photography, the same basic principle underpins pinhole imaging in other fields, such as short-range gamma-ray and X-ray imaging in medical and scientific applications, where a small aperture can form a simplified, magnified projection of a source.

In common usage, pinhole also denotes any very small aperture or defect that restricts passage of light or other signals.