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Astrophotography Guide

 

Click here for all Astrophotography Telescopes 


Astrophotography is one of the most popular aspects of modern astronomy. Determining what telescope, mount and other equipment to get though, can be a complex process.

Key considerations that will affect your decision are;
 
1.  What do you want to photograph?
 
  • Bright objects such as planets?
  • Dim deep sky objects such as star clusters, nebulae and galaxies?
  • Both bright and dim objects? 
  • 2.  How do you want to take your astrophotographs? There are several ways;
  •  
    • Piggy-Backing your camera to the telescope/mount
    • Aligning your point-and-shoot camera or phone to your telescope eye-piece
    • Using you telescope as a telephoto lens for your SLR (single lens reflex)digital or film camera – known as Prime-Focus Photography
 
93609-Universal Piggyback Mount with Camera-694 Universal adapter IS-100 06 new-image-600x547-599 Prime focus ETX-90 550Da-2j-743
Piggy-Back System Smart Phone and Adapter Prime-Focus System


Of the three methods Prime-Focus Astrophotography tends to be the most involved. 

Following are key considerations and information to assist you getting started with equipment selection for Prime-Focus Astrophotography.

In addition to your Digital Single Lens Reflex Camera ( DSLR)  there are three others items necessary for good prime-focus astrophotography.  :   
  
1. The Telescope for Prime-Focus Astrophotography.
 
To assist, following is an overview of key terms used when discussing telescopes for astrophotography.
 
  • Aperture-is the diameter of the main lens or mirror.
    •  It very important for visual observation but less so for prime-focus astrophotography. 
  • Focal–length is the distance form a mirror or lens to the image it forms.
    • It is a more important consideration in prime-focus astrophotography as the telescopes focal length determines the magnification.
    • Note the focal length can be increased with a Barlow lens or decreased with a focal reducer.
    • Greater magnification results in a smaller field of view
    • Lesser magnification results in greater field of view. 
  • Focal Ratio is the focal length / aperture. 
    • This is not important for visual astronomy but is for astrophotoghy the focal ratio is very important as it determines how quickly a photo needs to be taken
      • Fast (also called small) focal ratios are f/3– to f/7  needing shorter shutter speeds
      • Medium focal ratios f/7 to f/10
      • Slow ( aslo called long) f/10 to f/15 – needing longer shutter speeds
    • Note:  some cassegrain telescopes can have their focal ratio converted from f/10 to f/6 even f/3 making them ideal for a variety of applications.
 


Telescope Types for Astrophotography: 

Click here for a Summary table of the telescope types and their attributes 
 
1. Refactor Telescopes
 
  • Use a lens to gather light
    • Achromatic lenses are cheaper but can cause false colour in your image – a minus-violet can be helpful to minimise this.
    • Apochromatic lenses (also called Apo’s) are more expensive but can reproduce colour accurately.
    • The ‘glass’ used to make the lens is also a consideration with ED (enhanced dispersion) glass lenses producing a better quality image.
  • Tend to have shorter focal lengths giving a lower magnification and a wider field of view – good for deep sky images.  Higher magnification can be achieved with a Barlow lens.
  • Tend to have medium focal ratios – requiring shorter exposures.
 Meade etx80 dewshield frontangle2-804
  Refractors to consider for astrophotophotography
Meade ETX80
Meade-LX90-ACF-8-inch-695		 Saxon 909EQ
Saxon 909eq2 refractor telescope		 Saxon 1021EQ3
Saxon 1021eq3 Refractor		 Sky-Watcher Esprit 100 ED Apo
SW Skywatcher-esprit-100-143		 Saxon 120 ED EQ5
Saxon-ED120-EQ5
 
2. Reflector Telescopes
 
  • Use a mirror to gather light
  • Are the most inexpensive design
  • Do not suffer from false colour issues but can have some optical aberrations such as field curvature and diffraction spikes
  • Can lack “back focus” which means you cannot move the focuser in or out enough to get the camera to come into focus
  • Tend to come in a range of focal lengths
  • Tend to have fast to medium focal ratios
 Saxon 1309-EQ2 astronomy reflector telescope
   
3. Cassegrain Telescopes
  • Use a combination of lenses and mirrors to gather light.
  • They are compact, which makes they easy to transport and easier to balance on a mount
  • Whist compact are relatively heavy requiring a sturdy mount.
  • Tend to have longer focal lengths providing great magnification, though a smaller field of view – great for planetary and small target photography. For an image with a very wide field of view a focal reducer may be needed.
  • Tend to have a slower focal ratio though this can be changed depending on requirements in some models.
 Meade-LX90-ACF-8-inch-612
  

So… what telescope

 
The best type of telescope for astrophotography will vary greatly depending on the type of imaging you want to do.
 
Solar System imaging
Having said astrophotograpgy in general can be complex, it’s a nice surprise to find that taking amazing images of Solar system objects is relatively easy and inexpensive. If you can see the planets from your location, you can photograph them.
 
While the Moon can be photographed through just about any telescope and camera, the planets need more magnification because their apparent size is so much smaller.
 
Therefore telescopes for imaging planets have;
  • a longer focal length
  • a slow or longer focal ratio
Deep Sky Imaging
If you want to photograph faint galaxies, planetary nebulae and star clusters which are faint and vary in size
 
The telescopes for imaging large objects needing a wide field of view such as large nebulae have;
  • a shorter focal length
  • a fast focal ratio.
The telescopes for imaging small planetary nebulae and galaxies have;
  • a longer focal length
  • a shorter focal ratio and a lot of aperture.
 Following is a Summary Table of the types of telescopes suitable for astrophotography and their attributes.
 
  Aperture Focal Length Focal Ratio Field of View Aberation Stable Mounting Planets Deep Sky - Large objects Deep Sky - Small Objects
Refractor Small Short Fast
f/2-f/5		 Wide False Colour 
 		 Easy Tiny** Excellent Small
Reflector Medium
to
Large		 Med Med
f/6-f10		 Medium Coma / Diffusion spikes Medium Good Good Medium
Cassegrain Medium
to
Large		 Long Slow*
f10-f15		 Narrow None Compact though Heavy Excellent Poor*** Excellent
*This can be changed to med f/5 or fast f1.8 in some models
**This can be improved with a Barlow lens to increase magnification
***This can be improved with a focal reducer to increase the field of view
 
 
2.  The Mount
 
Arguably, this is the most important part of your setup and astrophotography is almost ­impossible without a good mount. Your equipment can get quite heavy and require much stability for long exposed images so if possible, always err on over­-mounting your telescope and camera.
 
A motorised tracking system is also incredibly helpful and without this you will be unable to take clear images of the planets, other than the moon or deep sky objects.  This is due to a long shutter speed being needed and as the earth is rotating, without a tracking system your object will move out of your image before sufficient exposure occurs.

3. The accessories
 
Click here for all Astrophotography Telescopes 
​sm visa