Astrophotography 101: Advice and Tips From Photographer Joshua Rhoades
When I saw the image above in my Facebook newsfeed, I was blown away! I had to know who took that stunning image! Joshua Rhoades is a photographer from Elkhart, Illinois. And I think its safe to say he is very modest when he says he is still in the "amature ranks". I was so excited when I asked and Joshua was happy to contribute a guest post for the blog about astrophotography! After reading this myself, I am beyond inspired by his talent, patience, and knowledge!
Likely you’ve seen the beautiful and seemingly unreal images of colorful wispy nebulae like those sent back to Earth from the Hubble Telescope. Perhaps images such as these have come across your social media feed (maybe some of them are my images!). While they may sometimes seem more art than photography, they make you pause and wonder what they are, how they are created, and question how exactly they are captured. How do we know these somewhat abstract and very colorful gaseous objects, surrounded by thousands of stars, really exist as depicted in these photographs? I mean, we surely don’t observe these objects in the night sky with our eyes. In fact, observation of these deep-sky objects is not possible visually (thanks short-exposure eyes). Even my light bucket (an 8-inch Schmidt-Cassegrain telescope) generates views of deep-sky objects that are...well, underwhelming. Stars through a telescope are still just points of light, and it becomes clear why deep-sky objects are termed “faint fuzzies” by visual observers. To satiate my curiosity of deep space, which began while observing Halley’s Comet through a telescope as a child, I embarked on a journey into the hobby of astrophotography. Now while I am very much within the amateur ranks (having been involved in astrophotography for only a couple years), I do have deep-sky photographs recently published in issues of both Sky and Telescope and BBC Sky at Night magazines. For me, it’s a hobby driven by curiosity and fascination, and I enjoy it as a blend of art, science, and technology (though at times it may seem more like research and data collection). Oh...and it’s technically a subset of photography too!
Astrophotography is a broad discipline that encompasses any photography of the night sky, from star trails and Milky Way photography to tracked sky photography and prime focus deep-sky astrophotography. It can be simple or complex. Here I’ll touch on the complex, jumping right into the deep end, but let me say that I quite enjoy spending summers shooting the Milky Way. Why summers? Well...the Milky Way has a season (approximately June through August) when the photogenic galactic core is located above our horizon in the southern night sky.
Deep-sky prime focus astrophotography requires a significant amount of specialized equipment. While a standard DSLR camera will suffice for many deep-sky targets, as in the case of the Orion Nebula, other deep-sky targets like the North American Nebula may require modifications to the camera in order to achieve more sensitivity to certain wavelengths of light outside of the visible spectrum (i.e. hydrogen alpha and ionized oxygen). In addition to modified DSLR cameras and specialized charge-coupled devices (some of which must be cooled when operating) a standard tripod will not suffice. Instead, a sophisticated tracking mount atop a substantial tripod must be used and be capable of being aligned with the North Star (termed polar alignment). Unlike wide-field night sky photography with a DSLR camera, there is little room for error when capturing photons through a telescope (even a telescope with a wide field of view). The potential for star elongation due to Earth’s rotation is relatively high, and small shifts in focus occur throughout the capture session due to expanding/contracting glass as a result of small temperature fluctuations. Since a telescope collects less light compared to a camera lens, exposure times for many of these dim deep-sky objects range from 120 seconds to 480 seconds per exposure (and you may collect anywhere from 10 to 100 exposures). With such long exposure lengths, there are obviously many sources of error when imaging deep-sky objects.
You may at this point think that the aperture of the telescope determines success in imaging. A larger aperture will allow more light to enter the scope and be recorded by the camera’s sensor, right? It is counterintuitive that this is not the case. Aperture is king for visual observation, as you need the telescope to gather as much light as possible to transmit to your eye. So if you’ve been thinking of purchasing a telescope for visual use - go big (plus, aperture fever is a real thing in astronomy!). If your budget allows, I suggest no less than a 6-inch aperture for visual observing. However, if you want to start imaging and be immediately successful, obtain a fast wide-field telescope, preferably an 80mm refractor, which will be significantly more forgiving for those long exposures than a slower and larger aperture telescope. Why a refractor? The optics are generally great with minimal chromatic aberration and the maintenance is minimal since typically no adjustments are necessary as with some other types of telescopes. Should you choose to get into the hobby, you will acquire more than one telescope anyway, much like you have probably acquired more than one camera lens. I currently have a Celestron 8SE 8-inch Schmidt Cassegrain for visual observing and lunar/planetary photography, a Skywatcher 130 DS Newtonian Reflector for imaging at a medium scale, and a Stellarvue SV80-Access 80mm refractor for wide-field imaging. Bottom line...there’s no single piece of kit that will do it all. But if I could only have one scope for imaging, I would keep my 80mm f/7 refractor due to the fast optics and the fact that there are countless deep-sky objects that are very large and fit nicely into its wide field of view.
As for the telescope mount I mentioned earlier, I currently use (and recommend for any beginner) a Celestron Advanced VX mount due to both its quality and affordability. Weighing in at nearly 75 pounds fully loaded, these tripods/mounts are substantial! Advanced computers and databases in the mount allow for precise go-to capability when setup properly and allow one to image throughout the night without the need for too many adjustments. Although this class of mount is relatively precise at tracking on its own, I use a camera inserted into a small 60mm refractor telescope (piggybacked atop the main telescope) to guide the mount and make small corrections to the tracking. The camera captures 0.1 second exposures via computer and analyzes the movement of a selected star in the camera’s field of view. If the mount is unable to keep that selected star within a specified tolerance on its own, the computer sends a signal to the mount to make small corrections to the tracking. The process is called guiding and is required for any exposure longer than 120 seconds.
Astrophotography can be overwhelming (I haven’t even begun to scratch the surface). Like any hobby it can be frustrating, as frigid nighttime temperatures and technical difficulties can be discouraging and the learning curve steep. However, when you begin to see a nebula, star cluster, or other deep-sky object, something you’ve never seen before take shape in front of you on your computer screen, you will be in awe! You will feel the same inexplicable pull to continue deeper...into the black hole that is astrophotography. Clear skies!
Thanks so much Kori for having me as a guest!
Thank you Joshua for this amazing post!!! Your work is stunning! I am positive that this has insired many photographers, including myself!
Do you have your own astrophotography images? I'm obsessed with them! Post your link to them in the comments!
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