Pinhole (optics)

A pinhole is a small circular hole, as could be made with the point of a pin.

[1][2] A small pinhole can act as a lens, focusing light.

This effect is also used in pinhole occluders, which are used by ophthalmologists, orthoptists, and optometrists to test visual acuity.

The same principle has also been applied as an alternative to corrective lenses: a screen of pinholes is mounted on an eyeglass frame and worn as pinhole glasses.

Besides pinholes made by the point of a pin, precision commercial pinholes are often made by laser drilling through a thin foil.