the writings and drawings of Leonardo da Vinci (1452-1519). At about the same period Daniel Barbaro, a Venetian, recommended the camera as an aid to drawing. He wrote: "Close all shutters and doors until no light enters the camera except through the lens, and opposite hold a piece of paper, which you move forward and backward until the scene appears in the sharpest detail. There on the paper you will see the whole view as it really is, with its distances, its colours and shadows and motion, the clouds, the water twinkling, the birds flying. By holding the paper steady you can trace the whole perspective with a pen, shade it and delicately colour it from nature." In the mid sixteenth century Giovanni Battista della Porta (1538-1615) made a huge "camera" in which he seated his guests, having arranged a group of actors to perform outside so that the visitors could watch the images on the wall. But the sight of upside down performing images was too much for the visitors and they panicked and fled, and Battista was brought to court on a charge of sorcery! It is likely that many artists will have used a camera obscura to aid them in drawing, but because of the stories of the occult, or because they felt it was "cheating" in some way not many people would admit to using one. In 1764, the lens was being developed. The name lens comes from the Latin word for lentil, because the shape of the lentils resembles that of a convex lens. In the sixteen hundreds Robert Boyle, had reported that silver chloride turned dark under exposure, but he believed that it was caused by exposure to the air, rather than to light. In the early seventeenth century Angelo Sala noticed that powdered silver nitrate was blackened by the sun, and in 1727 Johann Heinrich Schulze discovered that certain liquids change colour when exposed to light.At the beginning of the nineteenth century Thomas Wedgwood was conducting experiments in which he had successfully captured s...
