lens
a piece of glass or plastic that refracts light
bending parallel rays of light that pass through it
A lens forms an image by
light having a slower speed in the lens. (going from gas to solid)
All lenses rely on
real lenses
not made of many prisms, but of solid pieces of glass or plastic with surfaces that are usually ground to a spherical shape
converging lens (convex)
thicker in the middle and thinner at the edges, causing rays of light that are initially parallel to meet at a single poin
diverging lens (concave)
thinner in the middle and thicker at the edges, causing the rays of light to appear to originate from a single point
optical axis or principal axis
All lenses have....
principal axis
a line passing through the center of the lens perpendicular to the lens surface
focal point
the point at which a beam of light, converges
focal plane
a plane perpendicular to the principal axis that passes through the focal point of a lens
focal length
is the distance between the center of the lens and its focal point
change the path of light rays before they enter your eyes
Lenses are used to
convex lense
Used to correct farsightedness
convex lense
Image formed depends on position of image in relation to the focal point
convex lense
Refracts parallel rays of light so that they
meet at a True Focal Point
convex lense
form either real (inverted image) or virtual images
positive number
The focal length of a converging lens is always a
convex lense
also called a converging sense
magnification
occurs when the use of a lens allows an image to be observed through a wider angle than would be observed without the lens
di/do or hi/ho (height of image/height of object)
M =
a magnifying glass
a converging lens (convex lens) that increases the angle of view and allows magnification to occur (objects appear larger)
between the focal point and the lens
A converging lens will magnify when the object is
right-side up (virtual) and on same side as the object
(magnifying ) the magnified (enlarged) image will be
negative, because on left side of lens
(magnifying) The di will be....
real image (upside down)
(non magnifying) When the object is beyond the focal point of a converging lens, the image formed is called a
positive number on opposite side (right side) of the lens
(non magnifying) The Di will be a....
the rays do not converge, they never intersect (forward or back) and therefore NO image is formed
if the object is at the focal point,
projecting pictures on walls or screens
converging lenses are used for
concave lens................virtual images
Because light
rays never meet, ________ only produce _________
concave lenses
with this lense...... parallel rays of light are bent away from center of lens, the lens shape causes the light rays to spread apart and the Image seems smaller
concave lenses
Used to correct nearsightedne
concave.......left...... not seen
with a ________ lense, the focal point would appear to be
on the _____ side of lens since the rays spread out on other side, but a true forming of a focal point is ______
diverging lens........ spread out
Concave lens are a type of________, because the lens cause the light rays to _______
virtual, right-side up, and smaller than the object and on the same side of the lens as the object
When a diverging lens is used alone, the image is always
the viewfinder on a camera
A diverging lens is often used for
negative number because the di is a negative number (on left side of lens)
The focal length of a diverging lens is always a
ray diagrams
show the principal rays that can be used to determine the size and location of an image
The size and location of the object
image distance from the center of the lens
and the focal length
used to construct the ray diagram
1/f = 1/o + 1/i
This is called the thin-lens equation
The mathematical relationship between object distance o, image distance i and focal length f is given by:
graphically analyze how light rays behave when they pass through a lens and predict where the image formed will appear
Ray diagrams are used to
object distance
The distance from the center of the lens to the object
image distance
The distance from the center of the lens to the image.
focal point
the point where parallel rays of light meet ( or appear to
meet) after passing through a lens
represent the object
(convex) An arrow is used to
know the paths of two rays from a point on the object.
(convex) To locate the position of the image, you only have to
point at the tip of the arrow
(convex) Choose a ____________ representing your object
refracted by the lens to the focal point
(convex) A ray parallel to the principal axis will be
with no appreciable change in direction
(convex) A ray will pass through the center ......
emerges from the lens parallel to the principal axis
(convex) A ray that passes through the focal point in front of the lens
Pick a point on the top of the object and draw three incident rays traveling towards the lens
Drawing ray diagrams of diverging lenses 1
once these incident rays strike the lens, refract them according to the three rules of
refraction for double concave lenses
Drawing ray diagrams of diverging lenses 2
virtual,
right-side up,
reduced,
cannot be projected on a screen
The image formed by a diverging, concave lens is always
Telescopes
use a collection of lenses to collect and focus light from very distant objects
microscopes
uses combination of lenses to enlarge or magnify an image that is near
cameras
uses lenses to focus light and record image of an object
binoculars
pair of identical telescopes mounted side by side
camera
an instrument that works most like a human eye
convex lens and sensitive film (or light-detecting chip) mounted in a light-tight box
A camera consists of a
real, inverted image on the film or chip
A camera lens forms a
compound lenses to minimize distortions called aberrations
In practice, most cameras use
a shutter and a diaphragm
The amount of light that gets to the film is regulated by
that the film is exposed to light
The shutter controls the length of time
the opening that light passes through to reach the film
The diaphragm controls
a lens that forms a real image of a distant object
A simple telescope uses
eyepiece
The real image is projected in space to be examined by another lens, called the___________, used as a magnifying glass
the image produced by the first lens is within one focal length of the eyepiece
The eyepiece is positioned so that
enlarged virtual image of the real image
The eyepiece forms an
A pair of telescopes side by side, each with a pair of prisms
makes up a pair of binoculars:
a pair of prisms that flips the image right-side up
Each side of a pair of binoculars uses
two converging lenses (convex lenses) of short focal length
A compound microscope uses
real image of a close object
The objective lens produces a
virtual image of the first image, further enlarged
The eyepiece forms a
cornea
Light enters through the transparent, protective covering, the ______. It helps focus light and also helps to protect the eye.
iris
The amount of light that enters is regulated by the_____, the colored part of the eye that surrounds the pupil
the pupil
the opening through which light passes
converging........retina
Light passes through the pupil and through the _________ lens and is focused on a layer of light-sensitive tissue at the back of the eye�the ________
optic nerve
The image is then sent to the brain along the _________ in order to interpret the image and turn the image right-side up
fovea
a small region in the center of our field of view where we have the most distinct vision
the blind spot
a spot in the retina where the nerves carrying all the information leave the eye in a narrow bundle
upside down
In both the camera and the eye, the image is
altering the distance between the lens and the film or chip
In a camera, focusing is accomplished by
the cornea, the transparent membrane at the outside of the eye
In the human eye, most of the focusing is done by
changing the thickness and shape of the lens to regulate its focal length
The image is focused on the retina by
accommodation.........ciliary
This is called _______ and is brought about by the action of the _________ muscle, which surrounds the lens
nearsighted
can see close up, but objects at a distance are blurry
nearsighted
the eye focuses light in front of the retina because the eyeball is too long
nearsighted
Need concave lenses in glasses to see more clearly because it will spread out the rays (diverge) before entering your eyes, causing the image to form further back in the eyeball, on the retina
farsighted
can see at a distance, but nearby objects are blurry
farsighted
Here the eye focuses light behind the retina because the eyeball is too short
farsighted
Need glasses with convex lenses bc makes the rays bend toward each other (converge), before entering your eye causing the image to form on the retina so you can see clearly
1/focal length
Power =
diopter
The SI unit for the power of eyeglasses is the
1/fglasses = 1/do(glasses) -1/do(noglasses)
also power=
negative diopter
means the lens is a Concave (diverging ) lens used to
correct Nearsightedness
Positive Diopter
value for a lens used to correct Farsightedness
Astigmatism
a defect that results when the cornea is curved more in one direction than the other (soft images)
astigmatism
Usually it is caused by an irregularly shaped cornea, but can also occur with an irregularly shaped lens
astigmatism
The remedy is cylindrical corrective lenses that have more curvature in one direction than in another