Picture and Photography Ancient drawings and paintings of animals and humans are much older and more

7.2.2 Picture and Photography Ancient drawings and paintings of animals and humans are much older and more

vivid than the ancient writing of texts. People from another culture cannot decipher Egyptian hieroglyphics or a foreign alphabet, but they can all appreciate a horse painting from the Chauvet Grotto in France. To capture the likeness of a horse, the Chauvet artist needed great skill and experience, to represent in a few strokes all the

246 CHAPTER 7 INFORMATION

details that he considered important, while leaving out numerous other details. The camera obscura is a method to capture an image in great detail. It was described by Mo Ti in 420 BCE, and was known to Aristotle. Al-Hazen (965–1039) proposed its use for observing solar eclipses. In his Dream Pool Essays, Shen Gua (1031–1095) mentioned the reverse images formed by a small hole. He had used a dark box equipped with a pinhole, held at a variable distance from the receiving surface. Focusing was accomplished by varying the distance between the pinhole and the receiving surface, till the focus was sharp. A pinhole is easy to make, but it admits very little light so the resulting picture is quite dim. A later improvement came to camera obscura by replacing the pinhole with a single convex glass lens, which admitted more light but had the unfortunate property of chromatic aberration described earlier. Johannes Vermeer might have used the camera obscura to project

a scene onto a piece of paper, and then sketch the outlines with charcoal to produce

a highly accurate perspective. The steps involved in making a photograph may be described as: (a) gather and focus an image on a surface for inspection, (b) record and amplify the image and make it permanent, (c) display the image, and (d) make numerous copies of the image. The fleeting camera obscura image on the surface is not permanent, and has to be fixed or recorded before we have a permanent image. Many chem- ical substances are light sensitive, and change their chemical composition when exposed to light. The ability of the sun to darken silver salts was known as early as 1727.

light-sensitive substances. He dissolved bitumen of Judea in lavender oil and used the solution to coat a pewter plate, which hardened under light. After 8 h of expo- sure, he developed the picture by washing with a mixture of oil of lavender and white petroleum, which dissolved the unexposed bitumen that had not been hardened by light. After rinsing and drying, the picture became permanent, as the already hardened bitumen was no longer sensitive to more light. The exposure

ner, L.J.M. Daguerre, who was a scene designer and painter for the Paris Opera. In 1837, Daguerre used silver halide as the light-sensitive material, and mercury vapor as the developer, and was able to make clear and permanent photographs with

a reasonably short exposure of 20 min. Two years later, he developed a silvered copper plate, and exposed the plate to iodine vapor to form a layer of silver iodide that was also sensitive to light. The unchanged silver iodide was washed away with sodium thiosulfate, leaving the polished silver to form the shades. This product was called the daguerreotype.

An ideal photographic recording should have a portable surface covered with

a fine image material that is sensitive to light, so even a small amount of light would produce a microscopic latent image. The image material should have a dynamic range so that more light would produce a stronger latent image, and should also have a developer that amplifies the invisible microscopic latent images by a million times into visible images. Finally, there should be a fixer to wash away all the remaining unexposed image material so that the film is no longer sensitive to light for preservation. Earlier photographs used silver halide on a glass plate. Celluloid

247 was invented in 1873 by John Wesley Hyatt, and was used for photographic film by

7.2 RECORDS

George Eastman and the Kodak Company. The celluloid film with silver halide has been supplanted by modern electronics that are much more sensitive to light, and do not involve a “wet” processing. The “photomultiplier” is a photoelectric device that converts light into electrical signals. It was originally a vacuum tube, and can detect light and multiply the current by as much as 100 million times; the vacuum tubes have been replaced by semiconductor devices. Willard S. Boyle and George E. Smith of the Bell Labo- ratories invented the charge coupled device (CCD) around 1970, which is the most sensitive technology today for light and digital imaging, and is used in all the digital cameras. They used a capacitor to convert light into electric charges in proportion to light intensity, and then arranged many capacitors into a linear array. This array is then transferred to an amplifier and processed for recording. A two-dimensional image requires many such linear arrays of capacitors. Boyle and Smith shared a Nobel Prize in Physics in 2009, which was also won by Charles Kao for the devel- opment of fiber optics.

Our photographs are among our most cherished possessions, for memorable people and events. We preserve and display our pictures of weddings, holidays, children growing up, playing sports and music, sights and tourism. We remember the images of historic events such as the atomic bomb at Nagasaki and marines raising the flag on Iwo Jima. We also use photographs to show the faces of historical persons, to teach the science of nature, and to explain the principles of technologies.