Characteristics

Pinhole images are softer – less sharp – than pictures made with a lens. The images have nearly infinite depth of field. Wide angle images remain absolutely rectilinear. On the other hand, pinhole images suffer from greater chromatic aberration than pictures made with a simple lens, and they tolerate little enlargement.

Exposures are long, ranging from half a second to several hours. Images are exposed on film or paper – negative or positive; black and white, or color.

Pinhole optics, by the way, are not only used in photography. There is one animal in nature which uses a pinhole for seeing – the mollusk Nautilus. Each eye has an accommodating aperture – the aperture can enlarge or shrink. In this drawing, originally taken from a book published by Arthur Willey in 1900, the eye is the oval opening to the upper right.

History

Early Observations and Experiments

The basic optical principles of the pinhole are commented on in Chinese texts from the fifth century BC. Chinese writers had discovered by experiments that light travels in straight lines. The philosopher Mo Ti (later Mo Tsu) was the first – to our knowledge – to record the formation of an inverted image with a pinhole or screen. Mo Ti was aware that objects reflect light in all directions, and that rays from the top of an object, when passing through a hole, will produce the lower part of an image (Hammond 1981:1). According to Hammond, there is no further reference to the camera obscura in Chinese texts until the ninth century AD, when Tuan Chheng Shih refers to an image in a pagoda. Shen Kua later corrected his explanation of the image. Yu Chao-Lung in the tenth century used model pagodas to make pinhole images on a screen. However, no geometric theory on image formation resulted from these experiments and observations (Hammond 1981:2).

In the western hemisphere Aristotle (fourth century BC) comments on pinhole image formation in his work Problems. In Book XV, 6, he asks: "Why is it that when the sun passes through quadri-laterals, as for instance in wickerwork, it does not produce a figure rectangular in shape but circular? [...]" In Book XV, 11, he asks further: "Why is it that an eclipse of the sun, if one looks at it through a sieve or through leaves, such as a plane-tree or other broadleaved tree, or if one joins the fingers of one hand over the fingers of the other, the rays are crescent-shaped where they reach the earth? Is it for the same reason as that when light shines through a rectangular peep-hole, it appears circular in the form of a cone? [...]" (Aristotle 1936:333,341). Aristotle found no satisfactory explanation to his observation; the problem remained unresolved until the 16th century (Hammond 1981:5).

The Arabian physicist and mathematician Ibn al-Haytham, also known as Alhazen, experimented with image formation in the tenth century AD. He arranged three candles in a row and put a screen with a small hole between the candles and the wall. He noted that images were formed only by means of small holes and that the candle to the right made an image to the left on the wall. From his observations he deduced the linearity of light. (Hammond 1981:5).

In the following centuries the pinhole technique was used by optical scientists in various experiments to study sunlight projected from a small aperture.