Presented at the University of Guyana, May 2018

1. An Introduction to
Astrophotography
By Ferlin Pedro

2. Key Astronomical Concepts
• The Celestial Sphere
• Altitude/Azimuth Coordinates
• Light Spectrum

3. Celestial
Sphere

4. Alt/Az Coordinates
• Altitude is the angular distance of
an object above the local
horizon. It ranges from 0 degrees
at the horizon to 90 degrees at
the zenith, the spot directly
overhead.
• Azimuth is the angular distance
of an object from the local North,
measured along the horizon. An
object which is due North has
azimuth = 0 degrees; due East is
azimuth = 90 degrees; due South
is azimuth = 180 degrees; due
West is azimuth = 270 degrees.
• Source: http://spiff.rit.edu

5. Light Spectrum
• Light is measured in
nanometers (nm).
• Each nanometer represents
a wavelength of light or
band of light energy.
• Visible light is the part of
the spectrum from 380nm
to 780nm.
• Source: http://eyelighting.com

6. Types of Telescopes
• Two main types of telescopes are:
• Refractor
• Reflector

7. Parts of a Telescope
Example using a Refractor
Finder Scope
Objective Lens
Dew Cover Eyepiece
90 deg Mirror
Diagonal
Dovetail Mount Bar
Focuser
Image credit: Explore Scientific USA

8. How does a refractor work?
Image credit: Liverpool Astronomical Society
• Typical refractors have two lenses: a concave and a convex lens.
• The concave lens focuses the light given off by an object into one focus point (focal point).
• The convex lens spreads out the light from the concave lens to ‘focus’ light from a faraway object.

9. Key facts about Refractor Telescopes
• Uses lenses to produce an image.
• Inexpensive for small apertures; great for beginners. But gets
expensive as aperture increases; mainly for enthusiast.
• Refractors have an inherent problem of image distortion and
chromatic aberration (colored fringes).
• Expensive refractors (apochromatic) ‘corrects’ distortion and
chromatic aberration using specialized lenses.
• The famous Italian astronomer, Galileo Galilei, used a refractor that
was just under 2 inches long, magnifying at 30x.

10. Types of Telescopes (continued)
• Reflector (aka Newtonian Reflector)
Image credit: Explore Scientific USA

11. Key facts about Reflecting Telescopes
• Uses a combination of mirrors to gather and focus light – Primary and
Secondary.
• The amount of light gathering power is favourable since reflectors are
generally inexpensive for larger aperture sizes.
• Produces clearer images and no false colours.
• Best for observing large objects (e.g. Jupiter and Saturn) and faint objects,
such as galaxies and nebulae.
• An inherent flaw is ‘coma’, where stars in the field of view appears
‘stretched’ due to the curvature of the primary mirror. Can be corrected
with a ‘coma-corrector’
• English Physicist, Sir Isaac Newton, invented it in the 1680s.

12. How does a reflector work?
Image credit: Liverpool Astronomical Society
• No objective lens for light to enter. Instead, a concave mirror at the opposite end focuses an image of a faraway object.
• A small flat mirror redirects the image to the side of the telescope where the eyepiece is located.
• Light directly passes to the eyepiece, which then forms an enlarged image.

13. Simple Astrophotography Gear
• An inexpensive telescope with aperture ranging from 2”- 6”.
• A webcam or smartphone camera with 5-8 megapixals or better.
• Mounting accessories for webcam or smartphone to eyepiece.
• A sturdy tripod.

14. Smartphone
adapter

15. Example #1: Explore Scientific
90mm Refractor
• Telescope: 90mm Refractor
including Tripod - US$85
• Gosky Universal Smartphone
adapter – US$19

16. Budget Astrophotography
• Telescope aperture ranging from 3”- 8”.
• DSLR Camera with T/Adapter
• Sky Tracking Mount (Computerized or same as ‘Goto’)
• For DSO photography, an autoguider may be essential; guidescope
• Cost depends on components chosen, such as optional accessories
for imaging, better mounts, better telescope, type of photography
desired (DSO or planetary), etc.
• Software for image capturing and processing often used. Example,
BackyardEOS and Photoshop.

17. Example of a Budget Astrophotography
Setup
Image credit: astrophotography-tonight.com

18. Advanced Astrophotography
• Mainly for the enthusiast
• Professional equipment may include ‘correctors’ for inherent optical
problems (coma, chromatic aberration, flat-field).
• High-end DSLR CMOS (complementary metal-oxide-semiconductor)
cameras or CCD cameras (Charge-coupled device).
• Could be planetary or fainter DSOs.
• Larger apertures and longer focal lengths (e.g. 14” f/8 or greater).
• Autoguider will be necessary for DSO photography.
• Broadband vs narrowband imaging.

19. Example of an advanced setup
Image credit: astroanarchy.blogspot.com

20. Broadband vs Narrowband Imaging
• Broadband uses the three primary colours (RGB) combined.
• Narrowband focuses on specific bands of the light spectrum using
specialized filters (Ha-Hydrogen-Alpha, OIII-Oxygen II, Sii-Sulphur II)
• Narrowband follows the classic ‘Hubble Palette’.

21. Image source: swagastro.com

22. Constraints to Astroimaging
• Light Pollution (Can use filters or Narrowband imaging)
• Weather conditions
• Atmospheric conditions
• Wind
• Dew control (Dew prevention using dew caps, heating straps)
• Other factors: available funds, learning curve, time and effort, time,
and more time.

23. Stacking and Processing
• Combining images to reduce noise and other unwanted image
artifacts.
• Improves signal-to-noise, resulting in better image quality and detail.
• Reduces exposure time in the field.
• DSO – Photoshop, Nebulosity, Pixinsight, MaximDL
• Planetary – Autostakkert, Registax, Photoshop for processing.

24. DSO Stacking

25. Planetary
Stacking
Source: http://keithwiley.com

26. • THE END