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

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Introduction to Astrophotography

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Introduction to Astrophotography

Blythe Guvenen

Kitt Peak Visitor Center


Astrophotography

  • 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

  • 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.


Daguerreotype

  • First photographic plate, thin film of polished silver on a copper base.

  • Invented by Louis Daguerre in 1838


Early Astrophotography!First Lunar Daguerreotype 1840 - John Draper(20 minute exposure!)


Early Astrophotography!Henry Draper

  • First to photograph the Orion Nebula; September 30th, 1880

  • 50 minute exposure!


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?

  • 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)

  • 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

  • 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

  • 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

  • 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

  • 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

  • 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 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

  • Afocal

  • “Prime” focus

  • Eyepiece projection

  • “Piggyback”


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


Afocal Coupling


Afocal Photography


Digital Camera Adapters


“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” Focus

Cassegrain telescope

Off-axis guider

Focus on chip

Detector

Camera


WebCam Astrophotography


Schmidt Camera


Schmidt Camera


“Astrograph”


Questions?


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