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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

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Lec. 11: Ch. 4 –The Camera and Photography

Camera parts

Lenses for cameras

Controlling light

Photography as art

Photography as science

We

are

here

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Ansel Adams

1902-1984

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Ansel Adams

44Siege of Yorktown, 1861

James F. Gibson

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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.

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But first, let‟s understand the camera system.

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I. Camera parts

1. Lens

2. Shutter

3. Diaphragm

4. Focusing screen

5. Film (or digital

imaging chip)

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8

Camera parts

8

Lens

Sheet film

holder

Bellows

Shutter &

DiaphragmFocus

knob

This is an old-fashioned

view camera.

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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.

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Camera parts

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Sheet film

holder

Bellows

Shutter &

Diaphragm

Focus

knob

Lens

Produces the

image that you

want to record.

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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?

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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

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Some common lens focal lengths

40º

28 mm f. l.Wide angle

50 mm f. l.

normal

135 mm f. l.telephoto

15º

65º

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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

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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?

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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.

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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

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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

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F-number scale = factors of two in light

1 Big opening

1.4

2

2.8

4

5.6 Factors of √2 apart

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11

16 Small opening

Amount of light scales with area

Area scales with (diameter)2

more light

less light

Diaphragm has variable opening.

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What f-number scale looks like

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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

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Why can images be out of focus?

F

fuzzyin focus

Rays of light diverge on either side of the focal point.

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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

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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

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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

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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

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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

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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.

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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.

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Which gives more light?

A. shutter speed 1/4 sec

B. shutter speed 1/16 sec

Longer time open is more light.

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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.

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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.

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Lec. 9: Ch. 4 –The Camera and Photography\

Camera parts

Lenses for cameras

Controlling light

Photography as art

Photography as science

We

are

here

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Albert Bierstadt

Looking Down Yosemite Valley

Oil painting

1865

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Ansel Adams

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

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Wright Bros., 1903

Photography as proof. Jackalope, 2003?

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Alfred Stieglitz

1864-1946

Photography

as art

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Edward Steichen,

1879-1973

Glamour photography

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Edward Weston

1886-1958

Compare to 15th

century painting

with folded cloth

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Imogen Cunningham

1883-1976

Ansel Adams by Cunningham

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“Fine focus”

Means directional

lighting

“Soft focus” (not out of focus)

Means diffuse lighting

4343Ansel Adams

Snake River 1942

http://micro.magnet.fsu.edu/primer/java/mirrors/convex.html

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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.

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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.

Object distance, image distance, focal length

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XiXo

F

Magnification formula

S0 = object height

Si = image height

Note the similar triangles.

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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

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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

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For distant objects,

the image is at the focal point

(ask a burnt ant)

Demo: find focal length of lenses

Demo with your telescope

lenses.

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