The history of the lens

When was it invented, the little piece of glass that would change the world? No one knows for sure. By Peter Hennig

The Lens When was it invented, the little piece of glass that would change the world? No one knows for sure. By Peter Hennig In Ancient China, Greece, and Rome, they probably used 'magnifying-stones' of polished rock crystal, but it was not until about 1000 that the principles of the lens were properly described by an Arabic physicist, Ibn el-Haitam. His was not only the first correct account of how light is refracted by a lens, but also of how the eye functions in principle.

The microscope and the telescope
By the end of the sixteenth century it was known how a microscope worked. The basic model consisted of two positive lenses at a certain distance from each other, the one in front being small and strongly magnifying. It is a design that is not difficult to come up with if you sit experimenting with different lenses. Nor was the microscope seen as having any great significance to begin with. It was a curiosity that might entertain for a while, a 'flea-glass' that could turn the tiniest insect into terrible monster.
Even the telescope may have been discovered more or less by chance, although one version of the story credits its inventor with a more deliberate approach. It is said that in 1608 a Dutch lens maker, Hans Lippershey, received an order for two lenses. One was to be slightly larger and weakly convergent, the other to be smaller and concave, in other words a diverging lens. When the customer came to collect them, he held the lenses at arms' length from each other, smiled happily, paid, and left.
Lippershey was perplexed, and found no peace until he had cut two more lenses so that he could see what was going on for himself. To his amazement he found that a distant church tower appeared so close that he could see the weather vane quite clearly. News of the invention spread quickly, and only a short time later in Italy, Galileo Galilei began his pioneering study of celestial bodies.

A new world view
The human eye is quite weak in comparison with the eyesight of many predators. Yet we can see more than any other creature because we have supplemented our eyes with extra lenses.
During the seventeenth century, the lens started a formidable revolution in our ability to explore our surroundings and increase our knowledge, and gradually made it possible to alter our circumstances in a positive way.
The new optical instruments brought rapid improvements in navigation, with dramatic results for trade and shipping. Telescopes scanned the heavens - and the old world view died. Microscopes sought out the smallest details - and a whole new world was revealed that we had had no inkling of before.
This was a completely new branch of the tree of knowledge, and it changed our lives in many ways. New instruments that provided new information were fundamentally to change our way of looking at the world, but the lens also contributed change in less dramatic ways.
When it comes to gathering information and assembling knowledge at an individual level, the longer one can continue the better the results. Until the seventeenth century, most specialists ceased their active working life in their forties or fifties when deteriorating eyesight made any detailed work impossible. Once simple spectacles came within their means it meant there was something of a trade revolution, because they could stay active for another fifteen to twenty years. This era marks the beginning of the rapidly accelerating accumulation of knowledge that was to become the technical basis of the industrial revolution in the eighteenth century.

The elusive lens picture
Even the ancients knew that you could project a picture onto a wall when light shone through a little hole into a darkened room. Such large-scale pinhole cameras were in use in the fifteenth century. Sitting inside one, you could draw from the surprisingly bright images. When in the 1550s the hole was replaced with a lens, the brightness and definition increased so much that it became much more useful. In the seventeenth century portable camera obscura were constructed that employed the reflex mirror principle.
Of course people dreamed of being able to capture the 'pictures from nature' that the lens showed so beautifully, and there was an eager search for materials that reacted to light and could be used to record the images.

The discovery of the century
It is usual to date the birth of photography to the introduction of the Daguerreotype in 1839, but it could be said to have been essentially a reinvention - most of the technique was already known. The lens was known, the camera was known, and the reaction of silver salts when exposed to light had been known for a hundred years. What made it new was that everything was brought together, while the problem of making the silver salts sufficiently sensitive to light was solved, and a method was found of fixing the pictures so that they did not darken further when exposed to more light. If you tried to patent this under today's rules, it would be a matter of arguing for a second class patent, or a patent on a new application of an already known technique. Still, contemporaries saw photography as the invention of the century, a reasonable view considering the role photography would come to play.

The importance of the picture
Before photography's breakthrough, pictures were rare and exclusive. When King Gustaf III of Sweden employed Pehr Kraft the Elder to paint the portrait of Bellman, his pay was the equivalent of the price of a luxury car today. Accurate portraits and other sophisticated pictures were reserved for the upper classes.
I was reminded of the real importance of this when studying some eighteenth-century texts a couple of years ago. One text I read was a will with an explanatory letter, written by a well-educated, wealthy farmer. I can clearly recall from memory the ceremonious introduction: 'Now I have grown old, and the days of my life are drawing to a close...' He then wrote of his happy childhood and his strong, loving 'lady mother' who, as it was to turn out, set him on the right path in life. Then came the passage that almost made me drop my pen: 'I have come to realise that I can no longer see my mother's face.' He could no longer remember what his mother looked like; can the importance of the lack of visual information be expressed more clearly?

The image society
Through its accessibility and immense ability to convey information, the photograph has become all-pervasive. At the same time, it has become so obvious that we do not always appreciate its value - we cannot see the wood for the trees. The photograph has become one of our most important sources of information, used from morning until night in a never-ending flow. Modern information technology would certainly collapse without easily used imaging techniques.
In addition there are all the other areas where image-creating lenses are at work. Today we have telescopes that orbit the Earth equipped with powerful lenses that provide us with solid facts about events that could only be guessed at before. The last hundred years of microscope technology have been of vital importance to advances in medical science.
You can go on, listing field after field where image-creating lenses have been the cornerstone of our ever-increasing knowledge. It is not only that you can almost hear the wings of history as you focus your lens; you are, after all, using a technique that is on a par with fire and the wheel.

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