•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.
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•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
