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1
Physics 1230: Light and Color
Lecture 11:
Cameras, their parts and how to use them and
some Exam 3 review.
Reading: Chap. 5: The Eye part 1.
Exam 3 on Chap.3 in class on Wed.
HW8: Will be due Thursday, 5PM
22
Lec. 11: Ch. 4 –The Camera and Photography
Camera parts
Lenses for cameras
Controlling light
Photography as art
Photography as science
We
are
here
2
Ansel Adams
1902-1984
5
Early Daguerreotype
photos
5Poe, 1848
Paris, 1838
Subject must remain still for minutes.
Mercury droplets on polished silver.
Cameras existed for hundreds of
years (pinhole and lens versions)
The revolution (early 19th century) was FILM:
The method to store and reproduce the
images.
6
But first, let‟s understand the camera system.
7
I. Camera parts
1. Lens
2. Shutter
3. Diaphragm
4. Focusing screen
5. Film (or digital
imaging chip)
7
8
Camera parts
8
Lens
Sheet film
holder
Bellows
Shutter &
DiaphragmFocus
knob
This is an old-fashioned
view camera.
9
Two common kinds of cameras
• Point and shoot
One lens, viewfinder or
liquid crystal display (LCD)
Point and shoot digital
• Single lens reflex (SLR)
Interchangeable lensesSingle-lens reflex
LCD is on the back.
10
Camera parts
10
Sheet film
holder
Bellows
Shutter &
Diaphragm
Focus
knob
Lens
Produces the
image that you
want to record.
11
A Question
50 mm normal lens
85 mm portrait lens
Back o
f cam
era
You have a camera back and can use two different focal
length lenses to produce an image on the camera back.
(A) 50mm
(B) 85mm
Which lens produces the larger image size?
12
Focal length of lens determines
magnification and field of view• Short focal length = wide angle (more things in the image)
• Long focal length = “telephoto” (larger, but fewer things)
50 mm normal lens
85 mm portrait lens
Back o
f cam
era
13
Some common lens focal lengths
40º
28 mm f. l.Wide angle
50 mm f. l.
normal
135 mm f. l.telephoto
15º
65º
14
Zoom lenses have adjustable focal length
25 mm f.l. to 250 mm f.l = 10x zoom
Lens may have two fixed groups and two moving
groups to hold focus constant while zooming
15
Camera parts
1. Lens, focal length
2. Shutter (on the lens)
3. Diaphragm (on the lens)
4. Focusing screen or LCD
5. Film (or CCD chip)
We
are
here
Controlling the light that enters.
The Shutter: Opens the camera lens for
a controlled amount of time
You can open the shutter on your camera for
1 sec. or for ½ sec. Which one lets more
light energy hit the film?
16
A) 1 sec. because the light power is on longer
B) ½ sec because the light power is on less
C) The same, because the power hitting the lens is
the same in both cases.
D) None of these.
17
Shutter speed
The shutter controls the duration of the light.
Common shutter speeds
1/15 sec
1/30 sec
1/60 sec
1/125 sec
1/250 sec
1/500 sec
Each change lets in half the light.
FACTORS OF 2 in light
energy entering the
camera
18
F number controls the amount of light
Big diameter lens = low f-number, like f-number 1.4
Heavy. Cost more! Works in low light and indoors.
Small diameter lens = big f-number, like f-number 3.5.
For outdoors, weigh less.
d
F
opening ofdiameter
length focalf
Example: 200 mm focal length / 25 mm opening = f-number 8
19
F-number scale = factors of two in light
1 Big opening
1.4
2
2.8
4
5.6 Factors of √2 apart
8
11
16 Small opening
Amount of light scales with area
Area scales with (diameter)2
more light
less light
Diaphragm has variable opening.
21
Amount of light
f number Amount of light
1 100%
1.4 50%
2 25% or 1/4
2.8 1/8
4 1/16
5.6 1/32
8 1/64
22
Why can images be out of focus?
F
fuzzyin focus
Rays of light diverge on either side of the focal point.
23
What is depth of field?
Depth of field is how far objects can be apart
and still be nearly in focus.
F
Are not in
focus at the
same place
24
Here are two lenses. One is f-number 8 and the other
is f-number 2. The top lens is which one?
F
fuzzyin focus
big blur
small blur
(A) f-8 (B) f-2
25
f-number 8 has more depth of field (less blur)
than f-number 2
F
fuzzyin focus
big blur
small blur
More like a pinhole camera
26
Equivalent exposure settings (same light)
¼ sec. lets subjects move
Background in focus
(good depth of field)
1/250 sec. stops motion
Background out of focus
27
Equivalent exposure settings
These combinations give the same light
f number shutter speed
1.4 1/250
2 1/125
2. 1/60
4 1/30
5.6 1/15
8 1/8
11 1/4
Sports events, stops
motion.
Great depth of field, some
motion
28
Which is best for taking a picture of
a bird in a tree?
A. focal length 200 mm
B. focal length 50 mm
Longer focal length, larger image of a smaller
field of view. Telephoto lens.
29
Which gives more light?
A. f-number 4
B. f-number 22
f= F/D so SMALLER f-number is a larger D and
therefore, more light.
30
Which gives more light?
A. shutter speed 1/4 sec
B. shutter speed 1/16 sec
Longer time open is more light.
31
Which f-number gives half the light of f-4?
A. f-2
B. f-2.8
C. f-4
D. f-5.6
E. f-8
f = F/D, so you need a LARGER f-number for
less light. 5.6 is sqrt(2) smaller than 4, so twice
the light.
32
Which pair gives the same amount of light?
1/30 sec. and f number 4 and
a) 1/120 sec. and f-1
b) 1/120 sec. and f-2
c) 1/120 sec. and f-4
4x more light for ¼ the time.
3333
Lec. 9: Ch. 4 –The Camera and Photography\
Camera parts
Lenses for cameras
Controlling light
Photography as art
Photography as science
We
are
here
33
3434
Albert Bierstadt
Looking Down Yosemite Valley
Oil painting
1865
3636
William Henry Jackson. Mountain of the Holy Cross. 1873.
Photography replaced painting
to describe the western US
Albert Bierstadt
Looking Down Yosemite Valley
Oil painting
1865
41
Imogen Cunningham
1883-1976
Ansel Adams by Cunningham
42
“Fine focus”
Means directional
lighting
“Soft focus” (not out of focus)
Means diffuse lighting
48
Ray Tracing: One method to understand
spherical mirrors and lenses.
Example:
(A) Or (B):
The image is LEFT or RIGHT of the lens.
The image is REAL or VIRTUAL.
This device is the „magnifying glass‟. The
image appears larger than the object.
49
Ray Tracing: One method to understand
spherical mirrors and lenses.
Example:
What is the magnification?
SO
SI
SI is the image height
SO is the object height
I
O
SM
S Ray tracing plus a ruler to
measure things and you can
determine magnification.
Magnification formula
S0 = object height
Si = image height
Note the similar triangles.
51
Demo: big mama lens and bulb
We do the following: Image on opposite side of lens?
XI is positive (otherwise negative)
Image on opposite side of axis?
SI is negative. (otherwise positive) Object lengths are
ALWAYS POSITIVE.
The lens equation:
The land of “One-Over-Everything!”
FXX IO
111F = focal length
XO = object distance
XI = image distance
Usually, F and XO are given.
We want to find XI OI XFX
111
52
Distant objects:
Let Xo be very large, say 1,000,000 meters.
Then 1/Xo = 0.000001, which is very small. You can ignore it.
Then
FX I
11
For distant objects,
the image is at the focal point
(ask a burnt ant)
Demo: find focal length of lenses