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Chapter 3 Digital Cameras Lens Camera Lens Focal length Measured in millimeters (mm), e.g. 35mm, 50mm The longer the focal length, the more magnification of the scene. 100mm 300mm Fixed Lenses Compact digital cameras have fixed lenses Optical Zoom Digital Zoom Interchangeable Lenses

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chapter 3

Chapter 3

Digital Cameras

slide2

Lens

Camera

slide3
Lens
  • Focal length
    • Measured in millimeters (mm), e.g. 35mm, 50mm
    • The longer the focal length, the more magnification of the scene.

100mm

300mm

fixed lenses
Fixed Lenses
  • Compact digital cameras have fixed lenses

Optical Zoom

Digital Zoom

interchangeable lenses
Interchangeable Lenses
  • Digital single lens reflex (SLR) cameras have interchangeable lenses.
lens speed
Lens Speed
  • A fast lens has a large maximum aperture.
  • A slow lens has a relatively small aperture.
  • A fast lens is normally more expensive.

200mm f2.0

lcd displays
LCD displays
  • Most digital cameras have built-in LCD displays.
  • The LCD display of a digital camera allows the user to preview digital images taken.
  • Some digital cameras also use their built-in LCD displays as electronic viewfinders.
lcd displays8
LCD Displays
  • Advantages
    • Instant review
    • Movable LCD viewfinders extend camera-holding positions.
  • Disadvantages
    • Consume battery power
    • Some LCD displays are not bright enough for outdoors
    • Limited resolution and inaccurate colors could show misleading previews

LCD panel production

optical viewfinders
Optical Viewfinders
  • Advantage
    • Help save battery power
  • Disadvantages
    • On most compact digital cameras, optical viewfinders are separated from the lens and do not align with the sensor. (Worse for macro).
    • On most digital SLRs, optical viewfinders show a slightly “cropped” view of what the image sensor would receive.

Optical

viewfinder

Sensor

the shutter
The Shutter
  • Pushing the shutter button of a digital camera involves:
    • Charging the sensor
    • Activate the storage media
    • Meter for exposure and white balance
    • Auto focus
    • Etc.
  • Problem: Shutter lag
  • Solution: Half-press shutter button to pre-meter, and pre-focus.
storage media
Storage Media
  • Common types
    • CompactFlash (most common, biggest in size)
    • Microdrive (biggest capacity, most economical)
    • SmartMedia (getting obsolete)
    • Memory Stick (Sony)
    • xD-Picture (Fuji, Olympus)
    • Multimedia Card (MMC) / Secure Digital (SD)
  • Latest trend, smaller size
    • Mini-SD, RS-MMC, Memory Stick Duo
flash
Flash
  • Built-in flash
    • Main problem – too close to the lens in most compact digital cameras; tend to cause overexposure and red eyes
  • External flash
    • Some compact cameras also have sockets (hot-shoes) for external flash units – useful
image sensor
Image Sensor
  • A image sensor device is actually composed of millions of tiny light-sensitive sensors
  • When light hits the device, different sensors receive different amount of light
  • Each sensor converts the amount of light it receives into a corresponding electrical charge
  • Every electrical charge is then measured and recorded as a number (analog-to-digital conversion)
  • This is how an image is “digitized”.
bit depth
Bit Depth
  • An image is recorded digitally as a matrix of numbers.
  • Bit depth affects the possible range of each of these numbers.
  • E.g. 8 bits support 0-255; 12 bits support 0-4095
  • Higher bit depth supports “finer” image tone.
blooming
Blooming
  • When the amount of light exceeds the capacity of a sensor, the electrical charge could overflow or leak to adjacent sensors
  • Blooming occurs with high contrast scenes
noise
Noise
  • Unlike film grain
  • Digital camera noise caused by
    • Electronic interference
    • Various components of the digital camera could interfere the electrical charges on the image sensor
    • Heat is a major cause
ccd vs cmos sensors
CCD vs. CMOS Sensors
  • Charged Coupled Device
  • Complementary Metal Oxide Semiconductor
  • CCD sensors used to have better image quality and higher dynamic range in the past.
  • CMOS sensors have improved a lot and are being used in high-end professional digital cameras. See this link, link,
physical dimensions of sensors
Physical Dimensions of Sensors
  • Currently, image sensors come in different dimensions, e.g.
    • Canon 1Ds Mk II – 36mm x 24mm
    • Nikon D2X – 23.7mm x 15.7mm
    • Sony DSC-F828 – 8.8mm x 6.6mm
    • Canon A100 – 4.5mm x 3.4 mm
  • Compared with 35mm film:
    • 36mm x 24mm
sensor filters
Sensor Filters
  • Each sensor only captures the intensity of light, but not its color – “color-blind”
  • Each sensor actually has a colored filter in front of it – each sensor only sees one color
  • Red, green, and blue filters are arranged in some pattern to cover all sensors on a sensor device,
  • e.g. the Bayer pattern
color interpolation
Color Interpolation
  • A particular sensor only knows the intensity of one primary color; it guesses the intensities of the other two primary colors based on adjacent sensors’ readings
  • Could lead to inaccurate colors, undesirable patterns
dynamic range
Dynamic Range
  • The ability of a sensor device to capture the full tonal detail of an image from highlights to shadows.

The SuperCCD SR sensor device with extended dynamic range

Olympus Full Frame Transfer CCD