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Camera: Image
Formation
By
Heather Winchester
&
Krista Delucchi
In order to begin,
a vocabulary lesson is
necessary….

Vocabulary
Refraction
– deflection from a straight
path undergone by a light
ray or energy wave in
passing obliquely from one
medium (as air) into another
(as glass) in which its
velocity is different
– the action of distorting an
image by viewing through a
medium
– change of direction of a
wave: the change in
direction that occurs when a
wave of energy such as light
passes from one medium to
another of a different
density, for example, from
air to water
– degree of wave redirection:
the degree to which a wave
of energy is refracted
Vocabulary

Snell’s Law
– law governing refraction angle: the law stating that
for a light ray passing between two media the ratio
of the sines of the angle of incidence and the
angle of refraction is a constant
– 1/0 + 1/i = 1/f
Index of Refraction
Snell’s Law
Indexes of Refraction The refractive index of a substance measures how the substance affects
light traveling through it. It is equal to the speed of light in a vacuum divided by the speed of
light in that substance. When light travels between two materials with different refractive
indexes, it bends at the boundary between them.SUBSTANCE
REFRACTIVE INDEX*
Vacuum
1.0000
Air
1.0003
Ice
1.309
Water
1.33
Ethyl alcohol
1.36
Glass (fused quartz)1.46
Glass (crown)
1.52
Sodium chloride (salt)
1.54
Zircon
1.92
Diamond
2.42
* For light with a wavelength of 590 nm (590 x 10-9 m)
Microsoft ® Encarta ® Reference Library 2005. © 1993-2004 Microsoft Corporation. All rights
reserved.
Vocabulary

Converging
– meet: to reach the same point coming from different
directions
– arrive at same destination: to gather or meet at the same
destination
– mathematics approach finite limit: to approach a finite limit
as the number of terms in an infinite series increases

Diverging
– 1. separate: to separate and go in a different direction or
different directions
Vocabulary

Focal Point
– point where rays
from lens
converge: the
point at which
parallel rays
meeting a lens,
curved mirror, or
other optical
system converge
or appear to
diverge.
– Also called
principal focus
Vocabulary

Aperture
– in optics, the opening of a lens through
which light can enter. In photography, the
relative aperture, or f number, is the ratio of
the lens's focal length to the diameter of
the effective aperture—that is, the diameter
of the widest ray of light that can enter the
lens.
– Microsoft ® Encarta ® Reference Library 2005. © 1993-2004 Microsoft
Corporation. All rights reserved.
Image Formation in a Camera

Image captured using a lens

Lenses

If a piece of glass or
other transparent
material takes on the
appropriate shape, it
will be capable of
taking parallel rays of
incident light and
either converging
them to a point or
appear to diverge
them from a point.
Such a piece of glass
is referred to as a
lens.
A lens is merely a
carefully ground or
molded piece of
transparent material
which refracts light
rays in such as way
as to form an image.
Lenses can be
thought of as a series
of tiny refracting
lenses, each of which
refracts light to
produce their own
image. When these
prisms act together,
they produce a bright
enough image
focused at a point.
Lenses

Converging and Diverging
Lenses
http://www.physicsclassroom.com/
Lenses

Camera lenses are categorized according to
their focal lengths and maximum apertures.
The longer the focal length, the larger the
image inside the camera will be. The greater
the size of the aperture, the more light the
lens will admit. Focal length is the distance
from the optical center of the lens to the
image formed inside the camera. Because
this distance varies depending on how the
camera is focused, focal length ratings are
defined by measuring the distance when the
focusing ring is set for photographing a
distant subject (indicated on the focusing ring
with the symbol ∞, called infinity).
Lenses Continued

A lens with a short focal length is commonly
called a wide-angle lens; with a long focal
length, a telephoto lens. Lenses that
approximate the angle of view of the human
eye are called normal lenses.
 Focal length determines the magnification
and angle of view of the image. With the
camera in a fixed position, objects
photographed with a wide-angle lens will
seem farther away than with a normal lens;
seen through a telephoto lens, the same
objects will seem closer (and closer together).
The wide-angle can take in a broader angle
of view than the eye can see, while the
telephoto narrows this view.
Lenses Continued

The zoom lens offers a range of focal lengths.
 The zoom lens offers a range of focal lengths,
and is one of the most popular types of
lenses today. The user can change the focal
length by simply pushing a button or turning a
ring on the lens barrel. So-called true zooms
maintain focus while changing the focal
length; this allows photographers with singlelens-reflex cameras to focus precisely at high
magnification before framing the picture at a
different focal length. Another type of zoom
lens, the varifocal lens, must refocus as the
focal length changes—a disadvantage only if
the camera does not offer automatic focusing.

Microsoft ® Encarta ® Reference Library 2005. © 1993-2004
Microsoft Corporation. All rights reserved.