Lenses and Human Vision Lesson - PDF

How does the Human Eye Perceive Light? What is a lens? “ The difference between mirrors and lenses is that mirrors reflect light, whereas lenses refract light. A lens is a curved, transparent material that is shaped in such a way, that light refracts in a predicta...

How does the Human Eye Perceive Light? What is a lens? “ The difference between mirrors and lenses is that mirrors reflect light, whereas lenses refract light. A lens is a curved, transparent material that is shaped in such a way, that light refracts in a predictable and useful way. There are 2 types of lenses: a) Converging Lens b) Diverging Lens Let’s think...what type of lens is our eye? Converging Lens (Convex) A converging lens is also known as a convex lens. As parallel light rays travel through a convex lens, they are refracted toward the principal axis. Rays move toward each other, meeting at a focal point. Principal Axis Diverging Lens (Concave) A diverging lens is also known as a concave lens. As parallel light rays pass through a concave lens, they are refracted away from the principal axis. The rays move apart, never meeting on the other side. Principal Axis  Click on parts of the eye to find out their function! cornea iris retina Incoming pupil Parallel Light Rays Optic nerve ciliary muscles 8 Cornea - Outer surface where light enters - Thin like a credit card - Heals if scratched GO BAC K 9 Pupil - Dark, circular opening which allows light to pass through GO BAC K 10 Iris - Coloured part of the eye - Circular band of muscle that regulate the size of the pupil and how much light enters GO BAC K 11 Retina - Lining at the back of the eye which acts as a projection screen for incoming light rays - Brain inverts this image, so that it is right-side up GO BAC K 12 Ciliary Muscles GO BAC K 13 Light’s Journey Through The Eye As light rays hit the cornea of the eye, the light is refracted. The rays move through the pupil which is a hole that regulates the amount of light going into the eye. The iris makes the pupil larger or smaller, depending on how much light we want to come in. The rays continue through a converging lens where light refracts again. An image is formed on the retina, at the back of the eye. The image on the retina is real – meaning its upside down. Electrical impulses from the retina travel through the optic nerve to the brain where we “see” the image. We See With Our Brain via the Optic Nerve The optic nerve takes the inverted image from the retina and sends it to the brain which flips it so that the image we “see” appears upright. Our eye is used to gather light. But we actually see with our brain! Far-Sightedness (Hyperopia) Distant objects are seen clearly, but objects close-up are blurry. A converging lens in front of the eye helps the light rays form the image correctly on the retina. Near-Sightedness (Myopia) Nearby objects are seen clearly, but objects far away are blurry. A diverging lens in front of the eye helps the light rays form the image correctly on the retina.