pinhole eyeglass
Do this experiment in a well lighted place. Hold a newspaper
or book about 4 inches in front of your face. The words will
appear blurred. Make a hole in a piece of paper with a safety
pin. Place that paper in front of one eye as close as possible.
Close the other eye. Look through the hole to again read
lettering that is about 4 inches away. The letters will be much
clearer, although you can only see about a word at a time.
People who normally wear eyeglasses should try removing their
glasses and read print through the pinhole with the print at
normal viewing distance. They may find the print to be clearer.
Without the pinhole light from each point on a viewed object
passes through a large area of the eye's cornea and lens. An
entire scene falls on a large area of the retina. If any of
those eye parts are incorrectly shaped the image will be
distorted. This is the case with people who wear glasses.
The eye's lens actually changes shape when viewing scenes
at different distances. When the viewed scene is only a few
inches away the lens cannot change shape enough to be the
proper shape to produce a clear image.
The pinhole allows light to fall on only a small area of the
cornea, lens, and retina. In such a small area the actual
shape of the surface will not depart much from the ideal shape.
So the image is clear.