Cameras 1

CamerasCameras

Cameras 2

Introductory QuestionIntroductory Question

If you’re building a camera and If you’re building a camera and want to make a larger image (a want to make a larger image (a telephoto lens) you should:telephoto lens) you should:

A.A. increase the diameter of the lensincrease the diameter of the lens

B.B. decrease the diameter of the lensdecrease the diameter of the lens

C.C. increase the curvature of the lensincrease the curvature of the lens

D.D. decrease the curvature of the lensdecrease the curvature of the lens

Cameras 3

Observations about Observations about CamerasCameras

They record a scene on an image They record a scene on an image sensorsensor

Good cameras must focus, cheap ones Good cameras must focus, cheap ones don’tdon’t

They sometimes have zoom lensesThey sometimes have zoom lenses Some cameras have bigger lenses Some cameras have bigger lenses

than othersthan others They have ratings like focal length They have ratings like focal length

and f-numberand f-number

Cameras 4

Light from an ObjectLight from an Object

An illuminated object reflects or An illuminated object reflects or scatters lightscatters light

You see object via reflected or You see object via reflected or scattered lightscattered light

The object’s light forms diffuse The object’s light forms diffuse illuminationillumination

You can’t tell what object looks like You can’t tell what object looks like from this diffuse illuminationfrom this diffuse illumination

Cameras 5

Converging LensesConverging Lenses

A converging lens bends light rays A converging lens bends light rays via refractionvia refraction Light rays convergeLight rays converge Rays from a common point on an object Rays from a common point on an object

converge to a common point on far side converge to a common point on far side of the lensof the lens

Cameras 6

Real ImagesReal Images

An image forms in space on far side An image forms in space on far side of the lensof the lens

The image is a pattern of light in The image is a pattern of light in space that exactly resembles the space that exactly resembles the object, except for size and object, except for size and orientationorientation

The image is “real” – you can put The image is “real” – you can put your hand in ityour hand in it

Cameras 7

Lenses and Image SensorLenses and Image Sensor

Film records the pattern of light it’s Film records the pattern of light it’s exposed toexposed to

If you put film in a real image, it will If you put film in a real image, it will record a pattern of light resembling record a pattern of light resembling the objectthe object

For a good photograph, the real For a good photograph, the real image should be sharply focused on image should be sharply focused on the image sensor and have the right the image sensor and have the right sizesize

Cameras 8

FocusingFocusing

Light reaching lens from an object is Light reaching lens from an object is divergingdiverging

The nearer the object, the more its light The nearer the object, the more its light divergesdiverges

Converging lens has trouble with Converging lens has trouble with diverging lightdiverging light Real image of nearby object forms farther Real image of nearby object forms farther

from lensfrom lens Real image of distant object forms closer to Real image of distant object forms closer to

lenslens

1 1 1Object distance Image distance Focal length

Cameras 9

Focal LengthFocal Length

Focal length measures lens’ converging Focal length measures lens’ converging abilityability Long focal length: weak lens, long image Long focal length: weak lens, long image

distancedistance Short focal length: strong lens, short image Short focal length: strong lens, short image

distancedistance Larger the object distance, then bigger Larger the object distance, then bigger

imageimage Long focal length: big imagesLong focal length: big images Short focal length: small imagesShort focal length: small images

Cameras 10

Lens DiameterLens Diameter

Larger lensLarger lens converges more lightconverges more light brighter imagebrighter image focus becomes more criticalfocus becomes more critical less depth of focusless depth of focus

Smaller lensSmaller lens dimmer imagedimmer image focus becomes less criticalfocus becomes less critical more depth of focusmore depth of focus

Cameras 11

Introductory Question Introductory Question (revisited)(revisited)

If you’re building a camera and If you’re building a camera and want to make a larger image (a want to make a larger image (a telephoto lens) you should:telephoto lens) you should:

A.A. increase the diameter of the lensincrease the diameter of the lens

B.B. decrease the diameter of the lensdecrease the diameter of the lens

C.C. increase the curvature of the lensincrease the curvature of the lens

D.D. decrease the curvature of the lensdecrease the curvature of the lens

Cameras 12

Wide Angle vs TelephotoWide Angle vs Telephoto

Wide angle lensWide angle lens Strong to converge rays quickly and focus Strong to converge rays quickly and focus

closeclose Bright, small image forms near lensBright, small image forms near lens Small diameter lenses are usually adequateSmall diameter lenses are usually adequate

Telephoto lensTelephoto lens Weak to converge rays slowly and focus farWeak to converge rays slowly and focus far Dim, large image forms far from lensDim, large image forms far from lens Large diameter lenses are usually necessaryLarge diameter lenses are usually necessary

Cameras 13

Aperture or f-numberAperture or f-number

Aperture characterizes the diameter of the Aperture characterizes the diameter of the lenslens

F-number is focal length over lens F-number is focal length over lens diameterdiameter

Large f-numberLarge f-number Dim imageDim image Large depth of field/focus (focus is forgiving)Large depth of field/focus (focus is forgiving)

Small f-numberSmall f-number Bright imageBright image Small depth of field/focus (focus is critical)Small depth of field/focus (focus is critical)

Cameras 14

Lens FlawsLens Flaws

Dispersion Dispersion different colors focus different colors focus differentlydifferently Use low-dispersion glass (fluoride Use low-dispersion glass (fluoride

glasses)glasses) Use multi-piece lenses or “achromats”Use multi-piece lenses or “achromats”

Reflections Reflections fog in photographic fog in photographic imagesimages Use antireflection coatingsUse antireflection coatings

Cameras 15

EyesEyes Our eyes have lenses and an image sensorOur eyes have lenses and an image sensor

Unlike in cameras, eyes focus by changing Unlike in cameras, eyes focus by changing the focal length of the lens.the focal length of the lens.

Cameras 18

Digital CamerasDigital Cameras

Instead of film, use CCD imaging chipInstead of film, use CCD imaging chip Chip is divided into tiny squares or pixelsChip is divided into tiny squares or pixels Photon causes charge transfer in pixelPhoton causes charge transfer in pixel After exposure, pixels retain charge imageAfter exposure, pixels retain charge image Charge is shifted out of pixels using Charge is shifted out of pixels using

MOSFETsMOSFETs Camera obtains and saves imageCamera obtains and saves image