Pentax Camera

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Pentax Camera

• Julius Yellowhair
• OPTI 522A
• Fall 2003

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What is a camera?
Pinhole Camera
film plane
object
pinhole
My whole world is upside down.
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Pentax Cameras
Point shoot
Medium format
SLR
Digital
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SLR Camera

• What is it?
• Its a single-lens reflex (SLR) camera
• Very advanced camera system

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How does it work?

• Flip mirror allows the viewer to see through the
  lens, but swings up during the exposure of the
  film
• Advantages
• photographers ability to view a scene through
  the camera lens itself (the same lens that takes
  the picture)
• enabling precise framing
• viewing of the effects of focusing
• Disadvantages
• Bulky, very expensive

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Features

• Fully automatic mode point and shoot with
  automatic settings
• User-controlled mode set shutter speed,
  aperture, exposure, etc.
• Major features
• Auto focus 7 AF zones, CMOS sensors
• Viewfinder eye-level penta-mirror
• Exposure control metering, film speeds, shutter
  speeds

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Auto-focus mechanism 1Passive Image Coincidence
Rangefinder
Beamsplitter
?
Rotating Mirror encodes the scene distance

• Often used as visual aid for focusing
• Based on triangulation and parallax

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Auto-focus mechanism 2Passive Automated
Coincidence Rangefinder

• 2 images with parallax imaged onto 2 CCDs
• Signals from the 2 CCDs are compared to obtain
  image coincidence
• When both CCDs see the same thing, object is in
  focus

Line-of-sight
Reference
CCDs
Near object
Far object
Tilting Mirror coupled to lens motion
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Auto-focus mechanism 3Passive Automated
Coincidence Rangefinder
Viewing screen

• One detector array is optically coincident with
  the film plane
• 3 CCD images are analyzed for contrast
• Determines the direction of lens motion for
  focusing

Film
Flip Mirror
C B A
Beamsplitters
A
B
C
Move lens
In focus
Move lens
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Auto-focus mechanism 4Through the Lens Phase
Matching

• CCD is conjugate to the film plane
• Lenslets select light from part of the pupil

Lenslets
Film plane
CCD
Object focused inside film plane
Detector outputs
Object in focus
Object focused behind film plane
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Auto-focus mechanism 5Active Triangulation
LED
L
f
l

• Return spot on detector is kept in focused by
  tilting the detector array (Scheimpflug condition)

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New auto-focus technology

• Active infrared auto-focus system (7 zones)
• Based on the active triangulation extended to
  2-dimensions
• Two cases
• 7 LEDs, 1 detector, or
• 1 LED, 7 detectors

Seen through the viewfinder
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References

• J. Greivenkamp, OPTI 502 class notes, Fall 2003.
• E. Hecht, Optics,
• Pentax corporate website, www.pentax.com.