Refraction | bend the light with lens
Refraction | bend the light with lens | ||
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The lens performs multiple jobs when it comes to gathering the light that the camera then shapes into a photograph. The lens frames all the subject matter and determines how close or how far away it seems. The lens controls how much light passes through it, and which subjects are in focus. Framing with a viewfinder and the zoom controls still needs your aesthetic judgment. But with most digital cameras, the lens is happy to do all the focusing entirely on its own. Whether you focus the camera manually or let autofocus do the job, focusing works because of what happens when light passes through glass or plastic. When light bounces off an object, the reflected light spreads out equally in all directions. Light travels at slightly different speeds depending on whether it's passing through plastic or glass or some other transparent medium, such as air or water. When a ray of light passes from the air into glass or plastic—the most common materials used for lenses—the light continues at an infinitesimally slower speed. It's like a speed limit enforced by the laws of nature. But if the ray of light is at an angle to the plane where air and glass meet, not all parts of the ray move at the same speed as they cross from air to glass. The edge of a light beam that hits the glass first slows down while the opposite edge, still in the air, continues to move at a faster speed. The difference in speed results in the beam of light traveling in a different direction. The effect is similar to a car that has its right wheels in sand and the left wheels on pavement. The right wheels spin without moving the car forward much. The left wheels, with more traction, push the car forward more than the opposite wheels, causing the car to skid to the right. The process of bending light to travel in a new direction is called refraction. How much a substance causes light to bend, or refract, is called its index of refraction. Refraction is the principle that allows a camera lens to create a sharp, focused image. | ||