Lenses and the Human Eye

This is a lens and this is a lens and this is a lens. In today’s video you will learn the basics of lenses and the
human eye. To begin with there are two types of lenses convex and concave. Convex lenses cause light beams to
converge on a point the focal point. In fact you can use this focal point to start
fires. Even the word focus means fire in Latin. Concave lenses cause light beams to
diverge and don’t have a focal point. Well, they
do, but its imaginary. You can trace these
rays back to where they seem to be coming from and that’s the imaginary focal point. A
convex lens can also be used as a magnifying glass. Hey, E pluribus unum. But a concave
lens has a magnification have less than one caussing objects to always look smaller. In fact another way to measure for the focal
distance of a concave lens is to look for the point at which the
image is half the original object’s size. To quickly find the focal distance of a
convex lens you want to look for the point at which the world flips from being upside down to right
side up. Find the point the nonsense point at which
no light is focused and no image is formed. Perhaps most important
use a convex lens is its ability to project images. Take a look at this. The
problem is these images always appear upside dow. Hey look Royce Hall. The same thing happens with
the human eye. We’re gonna be looking at the skeleton
using this human eye model. And was projected on the back you’ll see
what happens. But I have to turn off the lights. Don’t get scared now When light enters the eye the convex
lens focuses it on the retina in the back of the eye.
This image is of course upside down. You probably have long since
forgotten those blurry few months during infancy during which you train your mind
to see property. The human I actually contains two lenses one on the outside and one on the inside.
The one on the outside is called the cornea and you can feel your own cornea by
closing an eyelid and putting two fingers over in looking left and right. That little bubble you feel moving
around is the cornea, the outside lens. The lens on the inside
of the eye is called simply the lens and it changes
shape based on your focus whether you’re
focusing on close objects or faraway objects. And this opening
here is called the pupil. It can constrict to let in less light on a bright day. But what do you think
this will do? The cat eye pupil. How do you think that
will affect an image? Here the image of a light bulb is being
produced on the retina of this human eye model. When I insert the
cat’s eye pupil the effect is only two dim the image.
It does not destroy it. You see just because I blocked some the light
that’s going through doesn’t mean that I destroy the image. On
the contrary the same reason lights still make it
through to form the same image in the same place. Take a look at this
situation. Here the eye is unable to focus light
from near objects. We say it’s far sided. An inserted lens
of the right focal length corrects this, and the blurry image is
made clear.