If you’ve been shooting (landscape) astrophotos for a while but are relatively new to astronomy, you may be contemplating stepping up to a telescope for your astrophotography. But taking the next step isn’t as simple as getting a longer lens for more magnified views. You should understand the changes in your shooting and equipment that this implies.
For most landscape astrophotography, much of the emphasis is on what is in the foreground — an interesting person, landscape, or city-scape, with a night sky backdrop (usually the Milky Way). But for telescopic astrophotography, unless you plan to stick to photographing only the moon and sun against the landscape, the objects in the sky itself become the primary subjects. So, before committing to the plunge into the deep end of the pool, here are some recommendations for easing in.
Learning the Sky
Needless to say, it’s important to know what objects of interest are out there, just as you must know where interesting viewpoints are on our own Earth if you’re into landscape photography. You must also know other aspects such as how large the target subject appears in the sky, how bright or dim it is, when it can be seen, etc. Learning the coordinate system of the sky (Right Ascension and Declination) is important too and is no harder than understanding latitude and longitude on Earth.
While there seems to be an ever-growing number of YouTube videos from amateur astronomers, there is actually a great deal more to it than can be learned from a few 15-minute videos. Here, a well-organized book is a better resource. One “classic” recommendation I have is:
- The Backyard Astronomer's Guide by Terence Dickinson and Alan Dyer
While this book has been out for a while, it presents a well-organized walk through the practical aspects of amateur astronomy, including astrophotography. And if you have a little patience, the fourth edition of this book is due to be published in September 2021, undoubtedly updating the astrophotography equipment section to catch up to the rapidly moving technology changes that have occurred since 2002.
Planetarium Program: Stellarium
If you haven’t already gotten a planetarium program for your desktop PC for astrophoto planning, I recommend starting out with Stellarium. Even if you have an app on your phone or tablet (Sky Safari is a good one), I recommend using Stellarium on a desktop PC since a very widescreen with high resolution is very beneficial, allowing some labeling of objects without cluttering the display too much. With this program, you can start to become familiar with the deep sky objects — nebulae, clusters, and galaxies. Stellarium also has a provision for incorporating photos of your own horizon to create a virtual view of the sky against your familiar surroundings.
I also recommend using Stellarium to create seasonal or monthly screenshots of your own sky, then installing them as desktop wallpaper to help you in becoming familiar with the sky above you. Change them regularly and gaze at them out when you need a break from your daily tasks. The features in the sky should become as familiar to you as landmarks on the ground over time. And the next time someone asks you what that really bright light in the sky is, you’ll immediately be able to tell them it’s Venus!
Another item I suggest you invest in is a set of printed sky charts. Why do I recommend old-school paper star charts? Access speed, wide coverage, and high resolution. Star charts that cover the entire sky in say, 20 sheets, have enough detail to locate deep-sky targets and yet see their locations relative to other objects across the sky. Unless you are constantly traveling, you can pare down to half the charts to cover your hemisphere and even down to a third of those to cover just what you’ll be able to see for a few months at a time. I have accumulated a variety of charts (I have an interest in terrestrial maps too), but I find the best compromise of scale and objects shown is Sky Publishing’s
Don’t be alarmed at the reference date of 2000. This refers to the date of the coordinates of the objects plotted. Despite nearby stars, which may be moving and coordinate changes due to the wobble of the Earth’s axis, the inaccuracies are not at a level to be of concern to amateur astrophotographers.
Alternatively, some free printable star charts are also available, but unless you have a large format printer, I recommend purchasing the Sky Atlas series, which comes on large pages with a color option.
For shoot planning, with the help of field-of-view templates printed on clear sheets of plastic, you can rapidly frame your targets or compare the fields of view for various instruments. You can do that also on a PC planetarium program such as Stellarium, but the process is slower and less convenient as you have to pan and zoom to get the same functionality. Make the templates to match the field of view for the telescopes and camera sensors you are contemplating to see how well the interesting deep-sky objects fit in your camera.
If you want a deeper look into the sky (dimmer stars and smaller objects), Stellarium or other programs are much more convenient and can include millions of dim stars not available on printed atlases, but the ultimate printed deep-sky atlas is The Millennium Star Atlas. At the image scale of this atlas, the maps had to be packaged as 3 large, thick volumes, which are inconvenient to reference, to say the least. And sadly, this classic is no longer in print and can only be found in the collectible marketplace.
Scouting the Sky Locations
Before diving into the deep end of the pool by getting a telescope, astronomical mount, and astrophoto-specific camera, there are a few warm-up steps I recommend taking.
- Get your camera (DSLR or Mirror-less) camera modified for enhanced red sensitivity. Another option is to purchase one of the few commercial models, which are factory-designed for astrophotography such as the Canon Ra.
- Get an external intervalometer that can be programmed to take multiple long exposures on your camera in “bulb” mode.
- Get a star tracker such as the Star Adventurer.
Recommendation one is to allow you to capture photos of galactic nebulae, which are often defined by the glowing gas of ionized Hydrogen. Modification is an option (mainly for Canon or Nikon cameras), done by a few camera dealers who are experienced with the insides of consumer cameras. Basically, they replace the IR blocking filter in the camera with another one that does not cut so deeply into the red end of the spectrum. Typically, this modification is done for $300-$400 and, of course, will void the manufacturer’s warranty, so you may want to do this on an older model spare body or purchase a used body for just astrophotography.
Recommendation two is something you will probably need, as most cameras cannot do exposures longer than 30 seconds and many do not have an intervalometer function built in.
The star trackers are miniature versions of astronomical mounts, which can be mounted on a standard, though heavy-duty photo tripod. They will get you acquainted with the way astronomical mounts need to be pointed at the celestial pole and allow longer exposures by tracking the stars as the Earth rotates.
With a tracker compensating for sky rotation, you will be able to do longer exposures and use longer focal length lenses, but personally, I don’t recommend going much beyond a 100mm lens due to the weight of the setup. And though some trackers have an autoguiding capability, they are only motorized in one axis and require adding even more weight to the setup because a secondary scope and electronic camera need to ride along with your imaging camera. A computer is also necessary to provide the autoguiding function.
While it’s possible to do this (you’ll see numerous examples on YouTube), I don’t recommend it, because the weight and awkwardness of the mounting introduces many chances of adding problems and frustrations that have more to do with overtaxing the mount than doing astrophotography. Of course, if you believe overcoming these sorts of problems is the character-building challenge you’re after, then go for it!
An Exercise For You
With camera, lenses, and tracking mount in hand, my suggestion is to run through an organized exercise of picking some targets in the sky, perhaps whole constellations with interesting nebulae or galaxies and systematically photograph them with the goal of processing the shots as deep-sky astrophotographers do. This includes:
- Take multiple long exposures (e.g. two-plus minutes long) of the intended target.
- Take multiple dark frames (same exposure length) with the lens covered.
- Take multiple bias frames (shortest exposures possible) with the lens covered.
- Take flat frames, which are multiple shots of an evenly illuminated white screen before adjusting anything in the optics (focus, aperture, zoom, etc.).
Start with just a few shots (say four) of each type, then work your way up to 20 or 30 to see the improvements you get with more shots in your stacks. The purpose of this exercise is to:
- Get used to the kind of post-processing necessary to get the most out of deep-sky astrophotos.
- Assemble your own photographic survey of areas of interest in the sky to get an idea of what telescopic photos will be able to pick up.
You can get an even better idea of what you can target if you stop down your lenses to match typical astronomical telescopes (f/4 to f/7).
The processing details are beyond the scope of this article, but the software you can start with is free. I recommend starting with Deep Sky Stacker, which handles all of the aspects of astronomical image processing you will need. This step is usually referred to as image pre-processing or image calibration, as you will be left with an image that should then be processed in Lightroom or Photoshop for final color balancing, contrast, and the other normal photo finishing steps.
When you do end up with your photographic survey shots, you can match the visible objects with the star charts to give you a good idea of what will be possible with a telescopic setup when your adventure really begins! The other benefit is that your shots will help to familiarize you with the sky in general. This is helpful when going out with a telescope and your planned target is shrouded in clouds. With a good familiarity with the layout of the sky, you can quickly decide on an alternative target for the evening.
As a final note, I want to add that I haven’t gotten rid of my own tracker and wide lens setup. I still use my simple wide-field setup on most nights alongside my telescopic setups. Having a wide lens on a camera snapping “free” frames all night allows me to make time-lapse movies of the sky or capture meteors. And sometimes, the sky conditions just aren’t good enough for telescopic shots, so the wide shots keep me from having to go home completely empty-handed.