Lenses and Vision Topic #4

Types of Lenses A lens is a curved piece of transparent material Light refracts as it passes through the lens, causing rays to bend Lenses are generally made of plastic or glass

Types of Lenses (cont.) A double concave lens is thinner and flatter in the middle than around the edges – causes light rays to diverge

Types of Lenses (cont.) A double convex lens is thicker in the middle than around the edges – causes light rays to come together or converge

So where do we use lenses?

So where do we use lenses? Eyeglasses

So where do we use lenses? Eyeglasses Overhead projectors

So where do we use lenses? Eyeglasses Overhead projectors Movie projectors

So where do we use lenses? Eyeglasses Overhead projectors Movie projectors Telescopes

So where do we use lenses? Eyeglasses Overhead projectors Movie projectors Telescopes Cameras

So where do we use lenses? Eyeglasses Overhead projectors Movie projectors Telescopes Cameras Microscopes

So where do we use lenses? Eyeglasses Overhead projectors Movie projectors Telescopes Cameras Microscopes Your eyeball!!!

Your Eyeball The lens in the human eye is a double convex lens It takes light rays from objects and by refraction, focuses the light at a certain point In a normal eye, the light is focused to the back of the eyeball on a light-sensitive area called the retina

Eye Problems Some people have eyes that are too long or lenses that aren’t properly shaped The image forms in front of the retina These people are near-sighted – they have problems seeing distant objects

Eye Problems (cont.) Some people have eyes that are too short or lenses that aren’t working Therefore, the image has not formed by the time it reaches the retina These people are far-sighted – they have problems seeing close objects

Mr. Churchill’s problem Astigmatism occurs when the cornea or lens (or both) are not perfectly symmetrical Astigmatism is the loss of focus (or Refractive error) caused by this irregular shape.

Camera vs Eye In your eye, your eyelids open and close to limit the amount of light reaching your eye In a camera, the shutter does the same thing

Camera vs Eye In your eye, the iris expands or contracts to limit the amount of light hitting the lens and retina In a camera, the diaphragm does the same

Camera vs Eye In your eye, the iris expands or contracts to make the pupil bigger or smaller In a camera, the aperture is the same

Camera vs Eye Both in an eyeball and a camera, there is a lens However, in some cameras, lenses can be changed or added to give you a greater magnification

Camera vs Eye In your eye, the retina receives the images from the lens and then sends that to your brain via the optic nerve In a camera, film or the image sensor captures the image from the lens. The image is either printed or sent via a memory card or cable to a computer, similar to an optic nerve