SI Vault
Sarah Boxer
February 13, 1989
It's a blustery afternoon on the beaverkill River in New York's Catskill Mountains. The worm and night crawler vending machine in front of Bob Darbee's Sport Shop is busted. Small black clouds gather, conspiring to make one very large, very black cloud. It's dark enough to be twilight. Out on the water the fishermen wading the river, which is famed for its trout, are wearing sunglasses. In the bar of the Antrim Lodge other anglers are discussing why.
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February 13, 1989

Casting A Clear Eye On Fish

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In a 1937 article in a scientific publication called The Journal of The Franklin Institute, Land, who had devised the first artificial polarizing filters in 1928 and had come up with polarizing sunglasses in 1936, asked readers to visualize a ray of ordinary light as a rope with one end held by a person and the other end tied to a tree. The person sends ripples down the rope by shaking it—side to side, up and down, any old way. To explain how light gets polarized, Land described the rope as passing through a gate with vertical pickets—a polarizer. Now, no matter which way the person sends ripples down the rope, the only ones that make it through the gate to the tree are those that lie in a vertical plane, like the pickets of the gate.

To get rid of polarized light, you simply make it pass through a second polarizer that is at right angles to the first one—a horizontal-picket gate. Because only vertical light waves can pass through the gate with vertical pickets and only horizontal light waves can pass through the gate with horizontal pickets, zero light gets through. Every possible path for the light is blocked. This is known as the extinction phenomenon.

On a trout stream the water functions as the first gate, the sunglasses as the second. But water is not a perfect polarizer. That means that polarized sunglasses cannot block all the glare all the time. Reflected light is perfectly polarized only when the incoming light strikes the water surface in such a way that the ray that bounces off the water and the ray that goes into the water are at right angles. This phenomenon, if you must know, is called Brewster's law. David Kerko, supervisor of new products at Corning Glass Works in Corning, N.Y., says Brewster's law is "Mother Nature's help" to make polarized sunglasses work effectively.

Brewster's law sounds pretty specific, and sunlight is obviously not a single ray zooming to earth at one precise angle, but there is a surprisingly large variety of situations in which Brewster's law comes into effect. Assuming the water is flat, as on a lake on a still day, sunlight will hit it at the proper angle for a few hours a day. Even if the water is rippling—say the wind comes up, or you're fishing a stream—there's a good chance that the proper angle is being achieved throughout the day by much of the light. Rippling water has lots of facets. "It's as if a thousand suns are hitting the water," says Kerko. So if you wear polarized sunglasses on a stream like the Beaverkill, or on the saltwater flats of Biscayne Bay, much of the reflected glare will be blocked and you'll be able to see underwater more clearly.

Is that really necessary? No, according to Bury, who says, "You don't need to see the fish underwater. When a trout rises to eat a fly you see a bubble. That's how you know where it is. You have to learn to read the water."

Tim Brannon of Endwell, N.Y., is less emphatic but is philosophically in agreement with Bury. "Even if you see the fish, you usually don't catch the one you see."

Most fishermen, however, have adopted a catch-as-catch-can attitude. Joan Wulff, a former national fly casting champion, author of Joan Wulff's Fly-Casting Techniques and coowner with her famous fisherman husband, Lee, of a fishing school on the Beaverkill, points out that a pair of polarized sunglasses permits you to see the currents and better judge where to cast. "The surface of the water, the kind of flow, tells what's underneath it," says Wulff. "Trout often feed on the edges of current. They'll be in the eddies behind rocks, and if you recognize them, then that's where you cast.

"Say a fish flashes [rolls away from the fly at the last second, showing its silvery sides]. Or it comes under the fly, hangs there and tries to take it. Or maybe it just looks at the leader and doesn't like it. If you didn't have polarized sunglasses, you'd miss the whole thing. You don't have to sell polarized sunglasses to the fishing public. It's already sold on them."

Polarized sunglasses can cost as little as $8, or as much as $300 (for tinted lenses ground to a bifocal prescription and mounted in gold frames). According to Ray Hensler, director of research for the sunglasses division of Bausch & Lomb, in Rochester, N.Y., they can be made simply by sandwiching a polarizing lens (made of polyvinyl alcohol dyed with iodine) between two thin sheets of tinted optical glass. As long as the resulting lens is set in a fairly sturdy frame, and the wearer's nose is properly situated on the face and the face remains more or less upright, then the lenses will be oriented to block light that's been polarized by water. Some skiers now wear goggles with polarized lenses, because they are effective in blocking the glare coming off flat snow fields. Researchers, however, caution that ice may be more difficult to see through polarized lenses.

Polarized lenses can also be photochromic. These glasses darken when the sun gets bright and lighten when the sun disappears. Other glasses, polarized and nonpolarized alike, have lenses with a tint—most commonly amber or copper in color—which enhances contrast by blocking some blue light. Because blue light scatters more in the atmosphere than any other color of light and because blue light does not focus as precisely on the retina as other light, anything viewed in blue light is blurrier. If you get rid of it by looking through amber-colored lenses, you'll get a more focused image. Trap and skeet shooters swear by amber tints.

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