If you are going to do astrophotography, you have a lot to set up and, later, to put away. This article cannot possibly replace the instructions for any of your equipment. Rather, I intend it to give you a basic idea of how much work is involved, when to do it and in what order, and how to prepare.
I suggest doing the following steps in order presented here, an order that tries to make the best use of daylight and dusk, so you are ready to make the best use of total darkness when it arrives. Adapt these steps to your own unique circumstances as you gain experience.
This article assumes you are setting up portable equipment for astrophotography, whether in your own yard or at a remote site. If you have a permanent or semi-permanent setup, your steps will be different.
You hear and read a lot about the importance of dark adaptation when doing astronomy (giving yourself time – 30 to 60 minutes – for your eyes to become accustomed to the dark and then carefully protecting your night vision by avoiding all light, or by using only a dim red light when necessary). This restriction doesn’t apply so much for astrophotography: your eyes are not doing the work; the camera is, and it doesn’t require dark adaptation time. You can safely ignore dark adaptation if
- you are doing only astrophotography, not visual observation; and
- you are finding your targets with a Go-To system, not your eyes; and
- you are alone – not with other astronomers.
Under these circumstances, don’t struggle in the dark; use a light to help you while setting up. A small table lamp, a gooseneck lamp, a clip-on light, or a head mounted flashlight are all convenient. (Don’t try to do complex setting up with a flashlight held in your mouth. It’s not nearly as much fun as it looks.) However, remember your light will attract bugs. Personally, I’ve learned to work in the dark rather than having to deal with being harassed by insects.
Be sure to turn all of your lights off before you begin actually doing your imaging. Although you are not protecting your own night vision, you do need to keep stray light out of the camera.
There are times when dark adaptation is still important:
- If you are mixing astrophotography and visual observation, for example, by trying to locate your targets visually using star-hopping. Some equipment, such as flip-mirrors, supports this by allowing you to easily switch an eyepiece in and out of the optical path. However, most experienced imagers don’t do that; once you have a camera attached to the telescope, you are unlikely to do visual observation. Even if you locate your target by star-hopping, you’ll do so by repeated camera exposures, not with an eyepiece.
- If you are with other astronomers, such as at a star party, it is essential that you not use a light. You may not be worried about your own night vision, but you must not ruin the night vision of your neighbours. Even if your neighbours are also doing astrophotography, you won’t know when they are taking exposures; keep the lights off to remain welcome. If you are with other astronomers at a star party, even your laptop screen and indicator lights are probably too bright, and you will have to do something to dim the screen and cover the lights.
Finally, of course, once you are actually exposing images, it is important to keep stray light out of the telescope. You should have no lights on during this phase, and point your laptop screen away from the telescope.
Comfort and convenience
This may seem trivial, but you will quickly find it is not. You will be spending substantial time outdoors, working on your computer and waiting while things happen. It is important that you be comfortable for this process. This is not just a luxury – if you are uncomfortable you will make mistakes. You will need a small table, at least large enough to hold your laptop and some accessories, and you should have a small but comfortable folding chair. Dress warmly too – you will be surprised how cold you get when sitting still, outdoors, in the dark and damp.
Insect control will be important too, but don’t use insect spray near your equipment: if it gets on the mirrors or lenses it can damage the coating. If you must use a spray repellent, walk well away from your gear (and, especially, other people’s gear), and downwind, before spraying. Better still, find some other solution to your insect problem. If they are really bad, use protective clothing, including a mesh hat if necessary.
Recently, I have been using ThermaCELL insect repellers with great success. These small devices use a butane cartridge to heat a chemically-impregnated repellant pad and keep mosquitoes out of an area about the size of my scope seating area quite effectively, with no residue.
Assembling the mount and optics
Our first major chore will be to assemble the mount and optics. Again, do as much of this as possible before it’s dark. First, you have a lot of small fiddling parts to connect and that is much easier when you can see; second, you don’t want to be wasting your precious dark time assembling gear.
So, assemble your mount using the normal procedure. Since we are doing astrophotography, we can assume you are using either an equatorial mount, or a fork mount with an equatorial wedge. Do all the basic setup, including the coarse leveling and coarse polar alignment. Next, assemble all of the optics onto the amount, in the normal way. Pay particular attention to ensuring that the various clamps and fasteners are tight, since it will not be obvious later, in the dark, if they work loose.
Large telescopes may have electronic assistance for cooling, such as internal fans. Turn those on now, to give your scope plenty of time to drop to the external air temperature. Now, we should mention one of the unfortunate side effects of cooling: dew. If you are going to be out late, and for a long time, you will probably experience a build-up of dew on your main mirror, main lens, or secondary mirror. Some optical designs are more susceptible than others to dew, and you will quickly learn how big a problem it’s going to be for you. At the least, you will probably need an external dew shield, which you should attach now. If you’re using one of the optical designs that are particularly vulnerable to dew, you will need electric dew heaters, and you should install those now, although you will not need to switch them on until after dark.
Finally, a reminder: assembly may seem like a lot of work but remember that you also need to dis-assemble everything at the end of your imaging session – and you may be rushing because of a sudden threat of rain or an intolerable attack of mosquitoes. Remember to leave time and energy for disassembly; if you are disassembling your gear when you are cold, numb, and exhausted, you will make a mistake and break or lose something.
Next, you should set up all of your electrical and electronic gear, including all power and signal cables. (We did the mount first so we would know the appropriate distances that cables would have to reach.)
Use a heavy-duty extension cord if you have 110 V power nearby, and end with a good-quality power bar. Things are going to get damp – especially things on the ground – so use outdoor-rated cords. For a portable setup, you will need to have one or more heavy-duty 12 V batteries. Run all of the power and control cables to your computer, mount, camera, and other accessories.
This is a good place to give two pieces of warning advice:
First, for some reason, many control cables for telescope mounts use very low-quality and flimsy connectors. Power connectors and the connectors for auto-guider inputs and for drive motors seem to be particularly prone to being loose or breaking. Be very careful with the connectors on such cables. Build up a collection of spare cables as you repair or replace what fails, and bring the spares with you.
So, pay attention to keeping the arrangement of your cables neat, especially ensuring that they cannot snag on anything when the mount moves in its normal manner.
Generally, the best way to do this is to run your cables up the centre of the mount and then along the body of the OTA to wherever they need to terminate. Minimize extra slack in the cables, and keep any slack away from the moving parts of the mount.
Your next step should be to balance your mount in right ascension and declination. Again, do this before dark – there is no reason to waste your precious dark hours on this simple mechanical task.
In fact, it is a good idea to do a “trial run” of assembling all of your gear and balancing it on a different day before you even set out on an imaging session. The first time you set up for imaging, you may discover that you cannot bring your scope to a balance point in the normal manner. The camera and other accessories add weight to the eyepiece end of the scope, and you may need an additional counterweight to balance in right ascension, and extra weight or some other arrangement to get the declination axis to balance. The time to discover this, and make whatever arrangements are necessary, is ‘’before’’ you set out for imaging, not that evening.
On some mounts, some imagers recommend keeping the mount deliberately imbalanced to a very small degree, slightly weighted toward the East. This way, the weight of the OTA is always being lifted by the right ascension drive gear. If the mount is perfectly balanced, or imbalanced toward the West, then the drive gears may “wander back and forth” across the slight gap caused by the backlash in the gears, which will result in irregularities in the right ascension tracking. On mounts with significant backlash in the RA gear, a slight East-imbalance can improve tracking; but too much imbalance may overload the RA motor.
Not all mounts should be imbalanced in this way, and the amount varies (although it is always small). I found my Losmandy G11 mount benefited from this technique. I would bring the mount to perfect balance, then move the RA counterweight 5-6 mm in the direction that produced a bias toward the East. (Moving the counterweight down when it was on the East side of the mount, or up when it was on the West side.) I recommend you start with perfect balance, and just remember this technique as something more advanced to try later, especially if you have unexplained variation in your RA tracking.
Some higher-end mounts don’t require this, either because of more precise machining or because they use other mechanical means to eliminate backlash drift in Right Ascension. The Paramount, for example, preloads the RA gears with a spring so that deliberate imbalance is not required, and is, in fact, not recommended.
Next, you can do the one or two kinds of alignment that your mount requires: your equatorial mount or wedge-adapted fork mount will require polar alignment and, if it is a go-to mount, it will also require the appropriate alignment for the go-to system.
A word about these two different kinds of alignment: I frequently see beginners confused about the difference between the two.
- Polar alignment is used to ensure your mount tracks accurately enough for long exposure imaging.
- Go-To alignment (such as the common “two star” or “three star” alignment) is used only to set up the Go-To system to accurately point the telescope at targets. It has nothing to do with the accurate tracking of a target, once found, during a long exposure.
In online user groups, when one hears questions such as, “My stars are streaked. Does that mean I need to do a better two-star alignment?”, this is a confusion between polar alignment and go-to alignment. (A clarification: on some very advanced mounts, the sky model of the go-to system is used to make minor corrections to tracking, and can improve long exposures. However, no mount you are likely to encounter as a beginner has this feature.)
Although go-to alignment does not affect your mount’s tracking performance, the reverse does happen: polar alignment does affect the go-to performance. So, if you modify your polar alignment, you will need to re-do the go-to alignment.
You can do your rough polar alignment before dark, and you may also be able to do your go-to alignment at dusk, since you only need to see a few bright stars for alignment.
In practice, it is often best to do these two alignments in two passes: do a rough polar alignment in daylight, then do a go-to alignment at dusk. Then, do a more serious polar alignment, such as a drift alignment, and, finally, re-do the go-to alignment. With practice, you will be able to complete all of these steps before it is dark enough for imaging.
There’s a lot involved in setting up for imaging. The keys to making it a success are:
Now that we’re set up (or before would have been good too), let’s select a target to photograph.