Pinhole Camera

•pinhole camera also known as camera Obscura, or "dark chamber", is a simple optical imaging device in the shape of a closed box or chamber. In one of its sides is a small hole which, via the rectilinear propagation of light, creates an image of the outside space on the opposite side of the box.

•Images created via a small opening will be found in the natural environment and in everyday life, and people in various parts of the world have been observing them since ancient times. Probably the earliest surviving description of this kind of observation dates from the 5th century BC, written by Chinese philosopher Mo Ti.

•The Western hemisphere, Aristotle in 4 BC was asking, without receiving any satisfactory answer, why sunlight passing through quadrilaterals, for example, one of the holes in wickerwork, does not create an angled image, but a round one instead, and why the image of the solar eclipse passing through a sieve, the leaves of a tree or the gaps between crossed fingers creates a crescent on the ground.

•10 AD the Arabian physicist and mathematician Ibn al-Haitham, known as Alhazen, studied the reverse image formed by a tiny hole and indicated the rectilinear propagation of light.

•The another scholar during the Middle Ages who was familiar with the principle of the camera obscura, namely the English monk, philosopher and scientist Roger Bacon. It was not until the manuscript Codex atlanticus (c. 1485) that the first detailed description of the pinhole camera was set down by Italian artist and inventor Leonardo da Vinci, who used it to study perspective.

 

Principle of a pinhole camera. Light rays from an object pass through a small hole to form an image.

•The camera Obscura was, in fact, a room where the image was projected onto one of the walls through an opening in the opposite wall. It was used to observe the solar eclipse and to examine the laws of projection. It later became a portable instrument which was perfected with a converging lens. Instruments of this kind were often used as drawing aids and, at the dawn of photographic history, they formed the basis for the construction of the camera.

•During the mid-20th century scientists discovered that it could be used to photograph X-ray radiation and gamma rays, which the ordinary lens absorbs.

•1850 the first photograph taken with a pinhole camera was the work of Scottish scientist Sir David Brewster the technique became more established in photography during the late 19th century when it was noted for the soft outlines it produced, as opposed to lenses generating perfect, sharp images.

         

• The image in the pinhole camera is created on the basis   of the rectilinear propagation of light. Each point on the surface of   an illuminated object reflects rays of light in all directions. The hole lets   through a certain number of these rays which continue on their course until   they meet the projection plane where they produce a reverse image of   the object. Thus the point is not reproduced as a point, but as a small disc,   resulting in an image which is slightly out of focus. This description would   suggest that the smaller the hole, the sharper the image. The calculations for   the optimal diameter of the hole in order to achieve the sharpest possible   image were first proposed by Josef Petzval and later perfected by British Nobel   prizewinner Lord Rayleigh. He published the formula   in his book Nature in 1891.
  

•The image created by a pinhole camera has certain characteristics. Since the process entails a central projection, the images in the pinhole camera are rendered in ideal perspective.

•Another special characteristic is the infinite depth of field which, in a single photograph, allows objects to be captured with equal sharpness whether they are very close up or far away.

•The pinhole camera takes in an extremely wide angle. The rays of light, however, take much longer to reach the edges of the negative than the centre, thus the picture is less exposed along the edges and therefore darkens.

•The disadvantage of the pinhole camera is the amount of light allowed through (small aperture), which complicates and sometimes prevents entirely the photographing of moving subjects. Exposure time is normally counted in seconds or minutes but, in bad lighting conditions, this could be hours or even days