Convex and Concave Lenses

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Convex and Concave LensesA Concave lens is

thinner and flatter in the middle, causing refracted light rays to diverge.

A Convex lens is thicker and rounder in the middle, causing refracted light rays to converge

The Human Eye & Sight

The Human Eye

Normal VisionThe eye is remarkable!Light that is reflected or emitted travels into the eye through the cornea. It passes through the lens and focuses on the retina at the back of the eye. Cells in the retina absorb this light and send the info along the optic nerve to the brain.

If your eye is functioning normally, the light image will converge at your retina, creating an inverted image.

The cillary muscles surrounding the lens contract and relax, therefore changing the shape of the lens.When the cillary muscles are

relaxed distant objects are focused on the retina, when they are contracted, closer images are focused.

cillary muscles

Nearsightedness (can see near)

A concave lens introduces divergence to correct focus.

The focal point of the light is to short to reach the retina. Light focuses in front of the retina.

Animation of Nearsightedness

http://www.mylasikdoc.com/html/eyesight.html

FarsightednessThe focal point of the light behind the retina short to reach the retina. Light focuses in behind

A convex lens introduces convergence to correct focus.

Animation of Farsightedness

http://www.mylasikdoc.com/html/eyesight.html