Digital Camera

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Digital Camera

• Essential Elements
• Part 1
• Sept 13 2007

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Basic Digital Camera

• Lens - usually with variable focal length to
  allow wide angle to telephoto view
• Shutter (either mechanical or electronic)
• A view finder to compose the image
• Sensor - an array of several million color
  filtered photo sensors, or pixels (the Bayer
  array) converts light (photons) to electrons
• An amplifier to modify sensor output
• An analog to digital converter to digitize sensor
  output
• A computer to convert the raw data to a visible
  image
• A Liquid Crystal Display to view image
• A data storage device usually removable
• A power source standard batteries or custom
  rechargeable battery

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Bells Whistles

• Automatic exposure
• Automatic focus
• Image stabilization (anti-shake)
• Live view
• Built in Flash
• Movie mode
• Adjustable image size compression
• RAW mode

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Simple Camera
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Compact Point and Shoot
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Super Compact (Image Stabilized)
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Super compact (folded optics)
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Super Zoom
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Hybrid
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Traditional
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4/3 format Digital SLR
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APS format Digital SLR
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Digital SLR Cross Section
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Digital Camera Concepts

• Lens Focal Length
• Focal Length Multiplier
• Depth of Focus
• Sensor Types
• Bayer Array
• Image Quality
• Digital Noise
• Dynamic Range

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Lens Focal Length

• The lens focal length for digital cameras is
  usually stated in terms of 35mm equivalent a
  carry-over from the most popular film format
• The true focal length is much shorter because
  most digital camera sensors are much smaller than
  the 35 mm film frame
• Normal zoom range is 3X to 4X
• Super zoom ranges from 12X to 15X

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Focal Length Multiplier (FLM)

• FLM is equal to the diagonal (43.3mm) in the 35mm
  film frame divided by the diagonal of the digital
  sensor.
• The concept is important on a digital SLR when
  older 35mm film camera lenses are attached.

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Depth of Focus / Depth of Field

• Depth of Focus is the distance on either side of
  image plane where focus is acceptable
• Acceptable is defined by the Circle of
  Confusion d
• d is approximately Sensor Diagonal(mm) / 1500
  
• Depth of Field is the distance in front and back
  of the object plane that will yield acceptable
  focus. When a lens focuses on a subject at a
  distance, all subjects at that distance are
  sharply focused. Subjects that are not at the
  same distance are out of focus and theoretically
  are not sharp. However, since human eyes cannot
  distinguish very small degree of unsharpness,
  some subjects that are in front of and behind the
  sharply focused subjects can still appear sharp.
• We can use smaller apertures for increasing the
  depth of field at some cost in terms of
  maximum sharpness of focus

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DOF Concept
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Lens Summary

• Consumer digital cameras are fitted with lenses
  with short focal lengths to create 35mm
  equivalent field of views on their small sensor
  surfaces.
• Because of the shorter focal length lens used,
  DOF, the depth of field, is much more than 35mm
  film cameras with the same field of view.
• This allows for economical automatic focus on
  digital cameras
•  
• Example Sensor diagonal 1/4 of 35 mm frame,
  lens set to 8mm focal length, F/4 aperture. DOF
  is equivalent to a 35 mm camera with 32 mm lens
  stopped down to F/16

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The Sensor

• CCD / CMOS are common types
• CCD (Charge Coupled Device)
• CMOS (photo transistor with on pixel
  electronics)

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CCD Sensor
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CCD Cross Section
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CMOS Sensor Array
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(2) Sensor Contd

• RBG Bayer Array
• A pattern of pixels with alternating R G B G
  filters that enable a computer to synthesize
  color. (The sensor has no color sensitivity)

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Bayer Layout
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Bayer Filter Array
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Bayer Interpolation
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(3) Sensor Continued

• Sensor Array Size seldom expressed in simple
  terms

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Common Sensor Sizes (Approximate)
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(4) Sensor Contd

• Megapixels Marketing emphasis because its
  simple, has some relevance and plays to
  conditioned response Bigger is Better
• Physical Size never expressed clearly
• The important dimensions are pixel pitch and
  number of active pixels
• Pitch defines the area of a pixel thus its
  light gathering ability
• Number of pixels relates to fine detail
  resolution