| A fascinating attraction at the University of Pretoria (UP) is the Sci-Enza Science Centre, a self-help laboratory where visitors can conduct their own experiments to acquaint themselves with basic natural laws. Part of the attraction is a camera obscura, which was completed in 1990 and is open to the public.
The Science Centre has moved to the Technical Building on the main campus, but the camera obscura is still on the roof of the Natural Sciences building (Natuurwetenskappe 1). Do not, however, expect to see a huge camera as you climb the stairs from the fifth floor to the roof.
Camera obscura is a Latin term which literally means dark room. And that is exactly what you will see - a dark room in which the development of the camera obscura from the pin-hole principle to a more sophisticated instrument consisting of lenses and plane mirrors is explained to visitors by the students on duty.
This predecessor of the modern photographic camera is eminently suitable to illustrate some of the optical functions of a camera.
The principle of the pin-hole camera was known to man in ancient times and was described in Chinese records dating back to the fifth century BC, as well as by Aristotle in the fourth century BC. What it amounts to is that a hole in the wall of a dark room between an object and a screen, will arrange the light reflected from the object in such a way that an inverted image will be formed on the screen. A large hole will give a fuzzy, but bright image, while a smaller hole will improve the sharpness of the image, but decrease its intensity.
When a converging lens is placed over a relatively large hole, an image is obtained which has the sharpness of a small hole and the intensity of a large hole. The image formed is still inverted and the simple lens tends to distort the edges of the image. One of the earliest references to the use of a lens in the camera obscura was made by Girolamo Cardano, a professor of mathematics in Milan in the 16th century.
Despite its shortcomings, the camera obscura was used extensively from the fifteenth century onward by artists as an instrument to copy images on paper. This application led to the design of many different types of portable instruments. During the eighteenth and nineteenth centuries many camera obscuras were also erected as permanent buildings and used for military, astronomical and meteorological observations, and also as tourist attractions. By then a mirror had been introduced into the system to direct the image either to the lens or from the lens to a screen. In South Africa Henry Carter Galpin built a camera obscura in Grahamstown in the late 1880s which is still in use today. Typical of its era, it has a single converging lens and a hollow screen which compensates for distortions.
The camera obscura at the University of Pretoria is a considerably more sophisticated instrument. Designed and constructed by the South African optical firm, Eloptro, it would probably be correct to claim that no other camera obscura has a better lens system than the one at UP - this according to Prof Lötz Strauss, now retired Professor of the Department of Physics. The lens system consists of three elements and projects a huge undistorted image of very high quality onto a flat horizontal screen.
The most striking aspect of the image on the viewing table is that people, cars, birds and aircraft actually move. The light enters the room by means of a special plane mirror which is housed in an adjustable turret that can be turned through 360°. From the mirror the light enters the lens and creates the image on a flat circular screen which can be moved up and down to facilitate focusing. By adjusting the direction of the turret, a different view of Pretoria becomes visible on the screen.
Towards the east the hills in Faerie Glen, the Menlo Park tower and Strubenkop as well as everything in between are clearly visible. The city centre is best viewed in the morning when it is illuminated by the sunlight from the east. On a very clear day it is possible to see vehicles on the pass in the Magaliesberg which leads to Pretoria North.
The images of the official residence of the State President and the Union Buildings are of such high quality that the colours on the flags can be clearly distinguished.
It is only on seeing these very sharp images on the viewing table that one suddenly realises that one is actually standing inside a large camera in the very position at which the images would in an ordinary camera be transposed onto the photographic film - inside a treasure room of vistas where nature paints her own pictures.