Introduction to Astrophotography

1. Introduction to Astrophotography Blythe Guvenen Kitt Peak Visitor Center

2. 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.

3. 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.

4. Daguerreotype • First photographic plate, thin film of polished silver on a copper base. • Invented by Louis Daguerre in 1838

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

6. Early Astrophotography!Henry Draper • First to photograph the Orion Nebula; September 30th, 1880 • 50 minute exposure!

7. The Human Eye • No permanent record of images. • No way to change exposure time. • No good way to measure quantitatively.

8. 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!

9. 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)

10. 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.

11. 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

13. 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)

15. 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

16. 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

21. 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

22. Astrophotography Using a Telescope • Afocal • “Prime” focus • Eyepiece projection • “Piggyback”

23. 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

24. Afocal Coupling

25. Afocal Photography

26. Digital Camera Adapters

27. “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!

28. “Prime” Focus Cassegrain telescope Off-axis guider Focus on chip Detector Camera

29. WebCam Astrophotography

30. Schmidt Camera

31. Schmidt Camera

32. “Astrograph”

33. Questions?