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Introduction to Astrophotography. Blythe Guvenen Kitt Peak Visitor Center. Astrophotography.

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introduction to astrophotography

Introduction to Astrophotography

Blythe Guvenen

Kitt Peak Visitor Center

  • Astrophotography is a specialized type of photography that involves making photographs of astronomical objects in the night sky such as planets, stars, and deep sky objects such as star clusters and galaxies.
  • Astrophotography is used to reveal objects that are too faint to observe with the naked eye.
  • Digital cameras
    • Can accumulate and sum photons over long periods of time.
  • Astrophotography poses challenges that are distinct from normal photography.
    • Subjects are usually quite faint, and are often small in angular size.
  • First photographic plate, thin film of polished silver on a copper base.
  • Invented by Louis Daguerre in 1838
early astrophotography henry draper
Early Astrophotography!Henry Draper
  • First to photograph the Orion Nebula; September 30th, 1880
  • 50 minute exposure!
the human eye
The Human Eye
  • No permanent record of images.
  • No way to change exposure time.
  • No good way to measure quantitatively.
to film or not to film
To film or not to film?
  • Pros:
    • Well-established
    • Archival quality (black and white)
  • Cons:
    • Finicky to temperature, humidity, processing conditions
    • Fragile; brittle
    • Low efficiency: 1-10%
    • Non-linear (reciprocity failure)
    • Difficult to get quantitative information
    • Nearly extinct!
charge coupled device ccd
Charge Coupled Device (CCD)
  • Semi-conductor based solid state detectors
  • Incoming photons generate electrons that are added up to form an image
  • Excellent quantum efficiency: 60-90+%!
  • Available for a wide range of wavelengths:
    • 300 - 1100 nm (Si)
    • 1 - 5 µm (InSb)
    • 1 - 25 µm (HgCdTe)
astrophotography using a camera
Astrophotography Using a Camera
  • Good quality, wide-angle photographs of the night sky can be made by almost anyone using a single lens reflex digital cameras.
  • Should travel far away from the bright, light-polluted skies.
    • Prevent the photograph from being completely washed out and ruined by bright urban light pollution.
fixed position mounting
Fixed-Position Mounting
  • Equipment needed
    • Camera capable of long (>30 sec) exposures
    • Sturdy tripod
  • Techniques
    • Amount of trailing depends on exposure time and declination
    • Digital stacking
    • Time-lapse
tracked wide angle shots
Tracked Wide Angle Shots
  • Equipment
    • >30 second exposures
    • Tracking mount
    • Piggybacked camera w/ lens
  • Techniques
    • Digital stacking
    • Foreground will trail (unless you use a flash to freeze it)
short exposure astrophotography
Short Exposure Astrophotography
  • Use CCD with “Hyperstar” or modified webcam
  • Short exposures = less expensive mount
    • Align and stack
    • Exact polar alignment is less important
    • Larger periodic error is tolerable
    • Unguided
long exposure astrophotography
Long Exposure Astrophotography
  • Good mounting is critical
    • Exact polar alignment is necessary
    • Solid connections (rings, plates, etc.)
  • Must be guided
    • Manual or auto
    • Need reticle EP or autoguider
long exposure astrophotography1
Long Exposure Astrophotography
  • Guiding
    • Piggyback
      • Need adjustable rings
      • Need larger mount
      • Differential flexure
    • Off axis guider
      • Can be hard to acquire guide star
    • Built in autoguider
      • Guides through filter  less sensitivity
astrophotography using a telescope
Astrophotography Using a Telescope
  • Afocal
  • “Prime” focus
  • Eyepiece projection
  • “Piggyback”
afocal photography
Afocal Photography
  • Simplest telescope coupling (unguided)

- Skylight filter recommended (protect camera lens)

  • Difficult alignment and focussing
  • Variable results - lots of patience!
  • Good telescope method to start with

- Digital cameras

  • Requires good quality eyepiece
prime focus
“Prime” Focus
  • Camera directly coupled to telescope
  • Telescope objective acts as very long focus lens
  • Camera replaces telescope eyepiece
  • Focusing easier than afocal method
  • Telescope guiding desirable!
prime focus1
“Prime” Focus

Cassegrain telescope

Off-axis guider

Focus on chip