|
Convex Lens
A convex lens curves outward; it has a thick center and thinner edges. Light passing through a convex lens is bent inward, or made to converge. This causes an image of the object to form on a screen on the opposite side of the lens. The image is in focus if the screen is placed at a particular distance from the lens that depends upon the distance of the object and the focal point of the lens. The lens in the human eye is convex, but unlike a glass lens, it is elastic so that it can change shape to focus on objects at varying distances. The lens becomes short and fat when viewing close objects and elongated and thin when viewing distant objects. Sometimes eye muscles are unable to focus light on the retina, the screen at the back of the eyeball. If the image forms behind the retina for nearby objects, a condition called farsightedness (hyperopia) results. Convex lenses are prescribed for hyperopics to assist the eye in making light converge on the retina for nearby objects.
From Principles Behind Lenses
|
