Lenses and Vision

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         As you can guess, a lens doesn’t always have to be glass. The first lens was a container of water. It was discovered by the ancient Roman writer Seneca (4 B.C.-65 A.D.?). He found that images became magnified when seen through a glass ball filled with water.

Roger Bacon (1214-1292?) invented the first convex lens in 1250. Concave lens were first used around 1450.

      Glasses were used in Italy around 1300. Old glasses were fastened with clips, rings, ribbons, weights, and other flexible things, or were simply held by the hand. Temples weren’t invented yet! They had frames of tortoiseshell, ivory, metal (heavy metal), or wood. They were pretty heavy. Temples were finally invented in the 1740’s. Lorgnettes (pronounced lorn-YETS) were also popular in the late 1700s. This word comes from the French word lorgner, meaning to leer at or stare. These were glasses held by a handle.

     Monocles were also popular. A monocle was a single glass lens that had to be squeezed by the muscles around the eye to hold it in place. Another popular kind of glasses was the pince-nez (panz-NAY) glasses, which pinched the nose to make it stay on. Both monocles and pince-nez glasses could fall off easily, so they both had ribbons or chains attached.

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     Contact lenses are pieces of plastic or glass that rest on the eye, separated from the eye by a thin layer of tears. They are newer than glasses. The first contact lenses were used in 1887. These ones were large and thick and not comfortable. The first modern contact lenses were made of a kind of plastic called PMMA (short for polymethyl methacrylate). These, however, did not let oxygen through to the retina (which is bad) so newer, more oxygen-permeable lenses were invented. The three kinds are: a combination of PMMA and silicone, one made of CAB (cellulose acetate butyrate), and one made of a Teflon-like non-stick fluoropolymer material. Also, soft lenses are also available. They were introduced in the 1970 and 80’s, are made of flexible, water absorbing plastics that become soft as they absorb water.

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    Hans Lippershey, a Dutch spectacle-maker, had an apprentice who held two convex lenses before his eyes, one near and one far away and could see a distant weathervane closer-up. He showed it to Lippershey, who developed the oldest form of a telescope: two convex lenses at each end of a tube. Galileo Galilei made a more powerful telescopes that he used to see craters on the moon, the moons of Jupiter, and the rings of Saturn.

     First telescopes were refracting telescopes, which simply refracted light. The first reflector was made by James Gregory.

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