DSO Astrophotography: What Equipment?

Astrophotography is quite a learning curve (I won't lie to you) but, man is it worth it!

It's expensive, complicated and time consuming but, once you've accepted (or dismissed) these aspects, your all ready to get some fantastic works of art captured light years away from Earth.

You'll spend hours capturing the data, followed by hours post-processing it and then you'll find that once the images are completed, you're desperate to get out and get more data. It's an endless cycle where the acquisition and tweaking becomes more absorbing and enjoyable than the results themselves - but what's wrong with that?

But before you get started, here's what you'll need equipment-wise (ouch!):  

 

Mount 

eq6

You're going to need an Equatorial Goto mount. A much sturdier Goto mount than for visual astronomy. That's because you need something that will eliminate any vibrations entering your scope (vibrations mean star trails during long exposure photography) and you need your mount to hold much more weight. Much more...

 

 

Telescope

refractor woflt132

Quite obviously you need a scope. Bigger scopes will allow you to get more detail but may have too much magnification for larger Deep Sky Objects. For big nebulae and galaxies a 90mm refractor is the biggest you'll want, whereas for faint nebulae and the smaller galaxies an 8" reflector or larger might be more suitable.

 

 

Guidescope

refractor orion80st

Next up is a guidescope. A smaller scope - usually around 80mm and a far cheaper model than your primary scope - will need to be piggly-backed or mounted side-by-side with your main scope. This houses a guiding camera (I'm coming to this) which will lock onto stars to ensure your mount will track the sidereal movement of the skies. Purists each have their preferred method of mounting a guidescope but your dedicated telescope retailer will weigh up your budget and setup to give you your best options.

 

 

Autoguider

autoguider setup

To ensure your mount won't stray from a fixed point, be it a galaxy or star cluster, you'll need an auto guider. This attaches to the guidescope and fixes onto a star within your field of view and forces your mount to keep this in the same position indefinitely.

You may be thinking that this is unnecessary with a Goto mount but even these mounts aren't accurate enough for photographic exposures of more that a couple of minutes - even with a perfect polar alignment.

 

 

 Field Flattener

field flattener

It's an inherent problem with refractors' curved lenses that stars towards the edge of view become elongated. This is often tolerable or imperceptible during visual use, but becomes prominent and intolerable in imaging. To correct this elongation ('comatic aberration', or 'coma'), you can use a field flattener. 

There will be a field flattener designed for your particular make and model of scope and it fits between the telescope focuser and the CCD or DSLR.  

 

Now your choices split two ways...

The CCD Route:


atik 314l a

A dedicated CCD camera attaches to your primary scope and can take rapid successive exposures for planetary images or very long exposure images for deep sky imaging.

Most CCDs have fans to keep the sensor cool and, thereby, reduce noise, while others use liquid coolants.This route produces the better images - but at greater cost.

 

 
laptop

CCD astrophotography requires a laptop or PC/Mac (if you have an observatory). But this allows you to slew to your target using planetarium software and EQMOD, focus with precision, store collected data straight to the computer's memory and process older images while you're taking new ones.

This is not a portable solution by any means but it is very solid & flexible.

 

filter wheel and filtersA filter wheel permits monochrome CCDs to record colour images by inserting red, green and blue filters and taking exposures in each colour - which are combined during image stacking and post processing. They're also useful for narrowband imaging using Hydrogen Alpha, Sulphur II and Oxygen III to recreate Hubble colours, for example. 
 

The DSLR Route:

 canon-eos-600dA standard DSLR camera can be attached to your main scope and used to take rapid successive exposures for planetary images or very long exposure images for deep sky imaging, using the 'bulb' setting'. Canon or Nikons are often preferred and megapixel count is king.

Having the IR filter removed by a skilled 3rd party will improve your astro-images but leave it useless for normal photography.

 


laptop or synguiderDSLR astrophotography often utilises a laptop in a similar way to CCDs but a Synguider or NexGuide allows you to be more portable as the images are stored on the camera's removable memory device and the slewing is done by the Goto mount. 

However, for precision focusing you'll need a liveview function on the DSLR with a 5x or 10x zoom capability or a Bahtinov_Mask

  


t-ring

To connect a DSLR you'll need a T-ring. Just remove the camera lens and insert the T-ring which will allow you to screw in a nosepiece (usually supplied) or attach it straight to your scope or field flattener.

Be aware that an EOS T-ring won't fit a Nikon and vice versa, so get the right on for your make of camera.