Concave Vs Convex

Focal length

Focal length (shown in red) is the distance between the center of a convex lens or a concave mirror and the focal point of the lens or mirror — the point where parallel rays of light meet, or converge.

Focal point• The focal point of a lens or mirror is the point

in space where parallel light rays meet after passing through the lens or bouncing off the mirror.

• A "perfect" lens or mirror would send all light rays through one focal point, which would result in the clearest image.

Anatomy of an Eye

corneaAs light enters the eye, it first passes through a lubricating tear film that coats the cornea. The clear cornea covers the front of the eye and helps to focus incoming light.

aqueousAfter light passes through the cornea it travels through a clear, watery fluid called the aqueous humor. The aqueous humor circulates throughout the front part of the eye, maintaining a constant pressure inside the eye.

irisThe iris is the colored part of the eye. As light conditions change, the iris may dilate to make the pupil bigger or constrict to make the pupil smaller. This allows more or less light into the eye.

lensAfter light travels through the pupil, it must pass through the lens. The human lens, much like the lens of a camera, is responsible for focusing light. The lens can change its shape to focus on nearby and distant objects.

vitreousAfter being focused by the lens, light passes through the center of the eye on its way to the retina. The eye is filled with a clear, jelly-like substance called the vitreous.

retinal vessels

The retinal blood vessels nourish the inner layers of the retina.

retinaThe retina is a thin, light-sensitive tissue lining the back of the eye that acts much like film in a camera. Light must be properly focused onto the retina, and the surface of the retina must be flat, smooth, and in good working order to produce a clear image.

maculaThe center, or bulls eye of the retina is called the macula. The macula contains a high concentration of photoreceptor cells which convert light into nerve signals. Because of the high concentration of photoreceptors, we are able to see fine details such as newsprint with the macula. At the very center of the macula is the fovea, the site of our sharpest vision.

choroidBehind the retina, a layer of blood vessels called the choroid

supplies oxygen and nutrients to the outer layers of the retina.

scleraThe white part of the eye is called the sclera. The sclera is composed of tough, fibrous tissue that protects the inner workings of the eye.

optic nerve

The optic nerve is a bundle of nerve fibers which carries visual information from the eye to the brain.

Light and Color

• Seeing color– You see what color is reflected by the object back

to your eye– Cones are cells in the back of your eye that detect

color– Rods are cells in the back of your eye that are

sensitive to light– Color blindness results from cone cells that do not

function properly in the eye

Common Vision Problems

Nearsightedness:Farsightedness:Astigmatism:

Nearsightedness : (Myopia)• Causes distant objects to appear

blurry• Occurs either because the cornea is

too curved or the eye ball is too long• Can be corrected by a concave lens .

Above: a myopic eye is longer than average.

Farsightedness: (Hyperopia)•Causes near by object to appear blurry•Occurs either because the cornea is not curved or the eye ball is too short•Can be corrected by a convex lens.

Above: a hyperopic eye is smaller than average.

Astigmatism:•Condition in which objects at any distance appear blurry•Occurs because the cornea or lens is misshapen.•Can be corrected by lens with two different focal points.

Color

• The colors present in white light in order of increasing

wavelength are: violet, indigo, blue, green, yellow, orange & red.

Roy G. Biv

Seeing Color 1

• An object absorbs all colors of light except the one that you see. For example, a red

shirt appears red, because red is the only color it sends to

your eyes.

Seeing Color 2

• A green piece of clear plastic appears green, because it only

allows green light to pass through it & it stops all other

colors.

Primary Light Colors

•White light can be broken down in the Primary Colors of

Light. These are Red, Yellow & Blue. All other

colors are combinations of these.

Seeing Colors 1

• Light enters the eye & is focused on the back on the

retina. • The retina contains two light sensitive cells, the rods & the

cones.

Seeing Colors 2

• The Rods detect the presence of absence of light. They are

mainly used for vision at night or in dim light.

Seeing Colors 3

• The cones give us our color vision. There are three types

of cones: red cones, green cones & blue cones.

Seeing Colors 4 • The brain interprets the

signals sent to it from these detectors & produces the

images that we see. Our sight is produced in the brain.

Pigments 1

• Pigments are colored materials that reflect some

colors of light & absorb other colors.

Pigments 2

• There are three Primary Pigment Colors: Magenta, Cyan & Yellow. By mixing

these pigments in different amounts we produce all

colors.

Pigments 3• Magenta absorbs Green and

reflects Red & Blue.• Cyan absorbs Red and reflects

Blue & Green.• Yellow absorbs Blue and reflects

Red & Green.

Colors & Pigments 1

• Primary Light Colors are known as the Additive Colors & produce White when seen

together.

Colors & Pigments 2

• Primary Pigment Colors are known as the Subtractive

Colors & produce Black when seen together.