The theory of Pinhole images from antiquity to the thirteenth century

Abstract

The principles underlying the camera obscura were first correctly analyzed by Ibn al-Haitham. In his Perspectiva (i.e., the thirteenth-century Latin translation of his Kitab al-manazir), al-Haitham describes the following observations, which are surely equivalent to what later became known as the camera obscura: The evidence that lights and colors are not intermingled in air or in transparent bodies is that when a number of candles are in one place, [although] in various and distinct positions, and all are opposite an aperture that passes through to a dark place and in the dark place opposite the aperture is a wall or an opaque body, the lights of those candles appear on the [opaque] body or the wall distinctly according to the number of candles; and each of them appears opposite one candle along a [straight] line passing through the aperture. If one candle is covered, only the light opposite [that] one candle is extinguished; and if the cover is removed, the light returns .... Therefore, lights are not intermingled in air, but each of them is extended along straight lines.1 Evidently rays of light passing through a small aperture (regarded as a point by comparison with the other dimensions involved in the experiment) remain distinct and cast a clear image on a screen behind the aperture; if all rays passing through the aperture should be considered, it is evident that the screen receives an inverted and reversed image of the entire scene opposite the aperture. But the case of " point-apertures" is a trivial version of the problem of images formed through an aperture. Since antiquity it had been recognized that even when the dimensions of the aperture are not negligible that is, when the aperture may not be regarded as a point light passing through it, under appropriate conditions, casts an image having the shape of the light source rather than the shape of the aperture. For example, the author of the Pseudo-Aristotelian Probternata calls attention to the anomalous fact that sunlight passing through quadri-