How Glasses Work to Correct Vision

How do glasses work?

You may be a person who needs glasses in order to see properly.

You may be farsighted ( hyperopia) which means you can see objects far away, but objects close up are blurry. This condition is created because the lens of the eye focuses the light beyond the retina.

A convex lens is usually used to correct this condition.

A convex lens is thicker in the middle than the edges. As a result, it refocuses the light and moves the focal point closer to the retina so that objects appear in focus.

When you are nearsighted (myopia) objects near to you are in focus and objects far away appear blurry.

This is because the lens of the eye focuses the light in front of the retina.

Concave lenses are used to correct this condition. A concave lens moves the focal point further away and directly on the retina.

In the video, I use a laser pointer and several different types of lenses to demonstrate how the focal point is moved either further away from the retina or closer to the retina. 

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Concave Convex Lenses

What is the difference between a convex and a concave lens?

Lenses are used in glasses, telescopes, microscopes, flashlights, and many more helpful objects.
A convex lens is a lens that is thick at the center compared to the edges. Convex lenses are also called converging lenses because as the light passes through the lens the rays come together at a focal point.
As the light passes through the lense it bends the light towards the center.
A convex lens is called a positive lense because the location of the focal point is in front of the lens.
A convex lens has the ability to magnify things and make them look bigger.

The human eye uses a convex lens to focus light and a convex lens can be used to correct long-sightedness or hypermetropia.

A convex lens is also used in a microscope and telescopes.

A concave lens is thicker at edges compared to the middle.
You can remember a concave lens because you are going into a cave.

It is also called a diverging lens because as the light passes through the lense they separate from one another.
As the light passes through a concave lens the light is bent outward from one another.

A concave lens is called a negative lense because the focal point is behind the lens.
It is used to correct short-sightedness or myopia.

Concave lenses are used in flashlights to spread out the light.
 Binoculars and telescopes use convex lenses to magnify objects and make them appear closer, but the image may be blurry. Binocular and telescope manufacturers use concave lenses in the eyepieces to help focus images more clearly.

Door viewers or peepholes use concave lenses in order to have a wide view of the area.

Summary Chart of Convex and Concave Lenses

	Convex	Concave
Structure	Thicker at the center compared to the edges	Thinner in the middle compared to the edges
Alternate Name	Converging Lens Positive Lens	Diverging lens Negative lens
Light Rays	Bend towards the center	Bend away towards the outside
Use	Our eyes, correct long-sightedness, hypermetropia, telescope, microscope	Correct nearsightedness, myopia
Focal Point	Positive focal point	Negative focal point

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