Digital Cameras

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Chapter 3

• Digital Cameras

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Lens

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

100mm
300mm
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Fixed Lenses

• Compact digital cameras have fixed lenses

Optical Zoom
Digital Zoom
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Interchangeable Lenses

• Digital single lens reflex (SLR) cameras have
  interchangeable lenses.

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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
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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.

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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
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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
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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.

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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

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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

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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.

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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.

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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

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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

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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,

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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

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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

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A microscopic view of a CCD sensor device
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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

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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