Insect Optics

Most optical instruments use lenses, mirrors or prisms to coax rays of light. This system works all right for microscopes and telescopes but not for the long, flexible probes (gastroscopes and broncho-scopes) that physicians use for peering into human stomachs and lungs. To permit the peerer to see around irregular curves, the instruments have to be packed with many small lenses, which absorb a lot of the light. Unless the field of vision is very small, the image is badly distorted before it reaches the eyepiece end.

According to Britain's Nature, copying the principle used in the compound eyes of insects may get around this difficulty. Instead of having a single lens, as human eyes do, to focus an image on the retina, insect eyes have many fine tubes, each tipped with a small lens. Each lens views a small part of a wide field, and the light that enters the lenses follows the tubes and forms a mosaic image. Some of the tubes are curved, but the light follows them just the same.

H. H. Hopkins and N. S. Kapany in Britain and A.C.S. van Heel in The Netherlands have copied this system by binding transparent fibers (glass or plastic) into compact bundles. When a lens forms an image on one end of the bundle, each fiber transmits a small part of it to the other end, where it shows as a pattern of bright dots, one from each fiber. The bundle can be bent into sharp curves, but the image follows it faithfully without losing its sharpness. If poked into a human stomach, it could give an insect-eye view of anything there.

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