Notes on eyes, vision problems, microscopes, telescopes, and cameras

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Eyes:Light tends to travel in straight lines.

Lens and cornea of our eyes bend light into a focused beam.

Cornea: outer most part of the eyes collects all the light that bounces off an object and focuses through a small hole (pupil).

Pupil: center of the eye, opens up wide more when its dark to let in as much light as possible.

Iris: opens and closes around the pupil, depending on the amount of light there is.

Lens: right behind the pupil, focuses the light onto the back of the eyeball. Clear, curved, changed shape depends on what kind of things you want to focus on, acts like the lens of the camera.

Retina: the back of the eye is coated with this special tissue, acts like the film of the camera, covered with photoreceptive cells (light sensitive cells)There are two kinds of photoreceptors on the retina: cones (6 or 7 million cones, can detect colors) and rods (more than 120 million rods, very light sensitive, can be even sensitive to a photon).

Lens projects image onto the retina, where the cones and rods transform the light and color into electrical impulses, and these impulses are transmitted up the optical nerve and into the brain, where the brain decodes the images.

When lens of the eye focus an image on the retina, its up-side down, but when the brain processes the images, it turns it back.

Raptors have eyesight 10 times better than ours. Eagles also do.

Vision problems:When light hits an object, it bounces off and is reflected into the eyes. Cornea and lens are light bending parts of the eyes; they focus the light onto the retina, a light sensitive tissue at the back of the eye.

Images are mostly focus onto the retina perfectly. But some peoples cornea is not shaped right, so they focus the image in front of the retina. Then the person is called myopic (nearsighted). Concave lenses refocus the light so it converges onto the retina.

Some people have cornea that focus light behind the retina. They are hyperopic...
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