This is a continuation of a general introduction to the tools and methods of astrophotography. We’ve discussed mount, telescope, and camera; now we need to have a computer and appropriate software to control the camera, and probably the mount.
Why You Need a Computer
To do digital astrophotography you will need a computer and some specialized software. This equipment has several purposes.
Controlling the Camera and Acquiring Images
If you are using a DSLR you may be able to do the actual acquisition of images without a computer at the telescope, just by pressing the shutter button on your camera and downloading your images from camera to computer later. (Most modern DSLRs, however, can be also controlled by a computer and there are numerous advantages to doing so.)
Specialized astronomy CCD cameras must be used with a computer at the telescope – they are incapable of being used on their own. Dedicated Astronomy CCD cameras also produce image files in a specialized format, and a computer will be needed to read and organize these files.
If you are taking long-exposure images, you will need an autoguider, and most autoguiders require a computer to do the analysis and calculate the guiding corrections to be sent to the mount.
Once you have taken the exposure and produced an image file, the job is far from over. (In fact, in terms of the time you will invest, it has only begun.) A substantial amount of post-processing of the image is usually necessary to make the captured detail visible and pleasing. This computer task is not normally performed at the telescope, but can be indoors, in comfort and during daylight hours or on cloudy nights.
Planning and Control
While not necessary, and not really a part of astrophotography, a computer at the telescope can also help align and control your mount, locate targets, manage your observing plan, and keep your logs and journals.
The remainder of this article offers advice on the selection of a computer and software for astrophotography.
Your imaging computer will be with you at the telescope every night, and may also be the machine you use indoors for your post-processing. It doesn’t have to be an ultra-high-end computer, but there are some features and specifications that you need to take into account. Let’s review some of the major choices.
Mac or PC?
I really like Macintosh computers. I have both Macs and PCs in my life, and prefer the Macs. I think they are superior in many ways, and always use a Mac when I have a choice. The web site you’re reading now was developed entirely on a Mac, as is most of my work.
However, my imaging computer in my observatory is a PC. Although there is imaging software for the Mac, and some cameras and telescopes include Mac control software, my experience is that the vast majority of drivers for astronomy devices are PC-only, and the vast majority of specialized astronomy applications are PC-only. Some of this software works in a Mac running Windows under Parallels or VMWare, but some does not. (When it doesn’t work, the problem is usually around the USB-to-Serial conversion that is often needed to run the Serial-port connection.)
If there was a way to do this with a Mac only, I would. However, the sad fact is you’re going to feel a strong need for a PC to do imaging.
My solution: both. PCs are cheap – especially considering that you don’t need a high-end one. So I have a PC in the observatory for telescope and camera control and image acquisition. Then, I have a Mac in the house on which I do my post processing (some with specialized PC software using Parallels), and then fine tuning with the Mac version of Photoshop.
There is Mac-native software available for many parts of the problem, and you might want to try to live that way. Your problem will be device drivers, so start by making sure you can actually talk to your camera. If you can’t make that connection work, nothing else will matter.
Update: I’ve recently converted my “mainstay” imaging control software from Maxim DL to TheSkyX(Pro). It is fully supported on both Mac and PC, and seems to support a generous number of cameras and other devices on the Mac-side. I suspect I could assemble a Mac-only imaging system at this point (but I’m not going to bother changing now). ASCOM (see below) is PC-only, but I suspect that by using TheSkyX(Pro) as the hub, I could manage without ASCOM, but at this point I’m not inclined to take the time to find out.
Laptop or Desktop?
Most beginner astroimagers will be using portable gear that must be set up at the beginning of a session and taken down at the end, so a laptop computer is the natural approach. A laptop also has the additional advantage that, being portable, it can come indoors with you after the imaging session and be your post-processing computer. The disadvantage of a laptop is its relative fragility. (I have already dropped one and damaged it, when cold and stupid at the end of an imaging session.)
If you have the luxury of a permanent setup for your telescope, you might want a permanently-installed desktop computer to go with it. However, remember that such a computer may be in a harsher environment than desktop computers are designed for – for example, it will be cold, and it may be damp with condensation (I’m assuming it will be inside a structure and won’t actually be rained on).
You don’t need a particularly fast computer for controlling a telescope and camera and acquiring images; the computer spends most of its time waiting for the telescope to move, or waiting for the camera to complete an exposure. In fact, even an older, used computer is probably fast enough.
However, you do want to make sure that the computer can respond to real-time events rapidly. For example, when autoguiding, the computer needs to calculate and send out the guiding correction commands within a second or two of taking a guiding exposure. A generous amount of RAM is a good idea, so the computer isn’t caught up in paging to disk when it should be responding, and, more important, you should configure various resource-intensive maintenance operations (such as software updates and virus scans) so they do not happen during your imaging session.
You do need good processor speed for post-processing. Calibrating, aligning, and stacking images, filtering them for noise, adjusting colour balance, etc., are processor-intensive tasks that will benefit from a fast processor. Most modern PCs have multiple processors and most processing software knows how to allocate work to take advantage of this, so a “multi-core” processor is a worthwhile investment.
RAM is always a good investment for a computer. It reduces paging, allows smoother multi-processing, and allows image processing software to run much more quickly. You should outfit your astroimaging computer with several gigabytes of RAM – it’s about the best performance investment you can make.
Astro-imaging takes up a lot of disk space, so you need either a large hard drive (many hundreds of gigabytes) or a large disk attached to your household network, or both.
Files produced by astro-imaging cameras and high-end DSLRs are quite large and you will be collecting a lot of files to assemble one finished image.
For example, a good-quality full-colour image of a nebula might involve capturing:
- 10 or more dark frames;
- 10 or more flat frames per filter (which means 40 or more flat frames if you are doing LRGB colour imaging);
- 10 or more actual image frames per filter.
So, for one finished product, you might collect 80 to 100 image files, each of which might be several megabytes in size. Then add several more copies of the image files as you go through the various stages of post-processing. This adds up to gigabytes of file space very quickly, for one final image product.
If you are using a PC (and you probably have to) it is a good idea to avoid the latest release of the Windows operating system. Not because it will be experiencing growing pains, although that is often true, but because there is a good chance that the device drivers for your camera and telescope won’t be available. Telescope and camera manufacturers don’t have the resources to run major software development labs, and they tend to be a release behind in the provision of drivers.
For example, at the time I was drafting this (2010), Windows Vista had just been replaced with Windows 7, and yet the 10-year-old Windows XP system was still the de facto standard for most telescope and camera control, with drivers for Windows Vista just starting to show up and become stable.
So, before you purchase your computer, check with the support community for your camera and telescope and make sure you understand what systems are supporting the necessary drivers.
This may cause you another problem: most large electronics department stores sell only the latest operating systems on the computers they stock, since their typical customers are doing routine home computing, not device control. So, if you want to buy a new computer running a late-model operating system you may find you need to shop at a smaller specialty store, or be prepared to “downgrade” the operating system yourself.
Some other considerations for your imaging computer include:
There are a variety of software packages you will need on your imaging computer. Some are “givens”, the drivers and control software needed to operate your camera, while others offer a variety of choices. This field is far too large to give a complete description here, but let’s do a quick overview to help you plan your system.
Image Capture Software
If you are imaging with a DSLR you might choose to capture images just using the camera’s built-in controls. However, most DSLRs can also be controlled externally with software, and dedicated Astronomy CCD cameras must be controlled externally with software.
Most cameras come with necessary drivers, and with basic imaging software capable of controlling the camera and capturing an image. Such software is often proprietary and limited in function. While it will do to get you started, you might wish to move to something more capable, and most cameras can be successfully connected to non-proprietary imaging applications through their proprietary drivers.
Proprietary Camera Software
You will find proprietary, device-specific image capture software included with most specialized planetary webcams (e.g. the Meade Lunar and Planetary Imager), and with entry-level CCD cameras such as the Orion Starshoot and the Meade DSI.
A web search will reveal a number of inexpensive, device-independent imaging packages. I have used and been impressed with Nebulosity by Stark Labs. It is inexpensive and very capable. And, unusually for astronomy software, it is available for both the PC and Mac platforms.
At the high end, there are a variety of commercial software packages for managing image acquisition and post-processing. These usually handle a broad range of cameras and other gear. Maxim DL from Diffraction Limited, the camera add-on to TheSkyX(Pro) from Software Bisque, and Nebulosity from Stark Labs are examples. (I am using TheSkyX(Pro) for most capture control, with CCDAutoPilot to automate bulk capture of darks and flats.)
Unless you are using a stand-alone autoguider, you need software to read the images from your guide camera, detect drift, and send corrections to the mount.
Feature of Comprehensive Software
Commercial comprehensive imaging software such as the Maxim DL and TheSkyX packages already mentioned have features to manage autoguiding. If you already have one of these packages, using the built-in autoguiding features may result in fewer things to run and configure, better integration with other functions, more status displays, etc.
Freeware and Shareware
There are some excellent free and shareware programs available for this purpose, such as “Guide Dog” and “PHD”. I’ve used PHD (“Push Here, Dummy”) from Stark Labs and find that it is easy to use and that it works very well. These inexpensive packages are usually limited only in the range of unusual cameras and mounts they can control, and in lack of integration with other functions.
Mount Control Software
Although it is optional, in a sophisticated setup you may also want to have your physical mount operation controlled by the computer. Most high-end mounts can be computer-controlled, and this can make your imaging more efficient by automating the location of objects, the location of suitable focusing stars, and the precise re-acquisition of objects for adding more exposure time later. Again, there are several options for this.
Feature of Comprehensive Software
Commercial comprehensive imaging software such as TheSkyX and Maxim DL have features to manage various equipment, including pointing your mount. If you already have one of these packages, using the built-in features may result in fewer things to run and configure, better integration with other functions, more status displays, etc.
Specialized Mount-Control Software
Some mounts come with their own specialized control software, and there are numerous inexpensive, limited-purpose programs available. It is worth taking the time to do an online search for your specific mount.
Another interesting option is that practically every Planetarium or Star Chart application has some capability to control a telescope. Examples of packages that can do this are Starry Night, TheSky, Stellarium, Carte du Ciel, etc. Since you probably have one or more of these packages anyway, it may be all you need.
On some of these packages the ability to point a telescope is basic, provided as a convenience. On TheSky, the capability is quite sophisticated and, in fact, TheSky is the only way to control the very high-end Paramount mounts.
Now we come to one of the surprises of astrophotography. After you have pointed your telescope and used your imaging software to capture an image with your camera, you may think your job is nearly done.
You have only begun. You may not even be able to see your target yet, and it certainly won’t look good enough that you consider it ready to save or publish.
You will probably need to combine multiple images to improve resolution or signal-to-noise, and doing this will also require precisely aligning multiple images. You will need to do Dark Frame Subtraction to eliminate camera noise, and probably also calibrate your images with Flat Fields. Then you will need to do multiple adjustments to the relative brightness of the colour channels, and adjustments to the contrast.
All these steps are collectively known as Post-Processing. Again, there are many choices of software available for this.
Feature of Comprehensive Software
Commercial comprehensive imaging software such as the Maxim DL, CCDSoft, and Nebulosity packages have post-processing features such as alignment, stacking, calibration, and level adjustments. They are a convenient way to do many of these tasks, and often include automated “do everything” features that combine all the necessary tasks into one operation.
Specialized Astro-Imaging Post-Processing Software
Moderately-priced, and even free, packages are available that focus exclusively on post-processing. CCDStack is the one that I use most of the time and ImagesPlus is another popular choice. By focusing on a single problem area, these packages tend to offer more comprehensive features with an overall simpler interface. They are often single-author products, so they may have less polished user interfaces and documentation than some of the large commercial offerings.
Specialized Video-Stacking Software
The above comments are somewhat biased toward the kind of software you would be using to process still photos of deep sky objects. If you are using a video camera to do Lunar and Planetary imaging, you will need software to process the captured video: selecting, aligning, and stacking a large number of frames.
Although there are certain other choices, and some of the commercial packages mentioned above can do this, the de facto standard in this space is Registax. It is an excellent shareware package specifically designed to select, align, and stack video frames into a final image. It’s complex and has a substantial learning curve, but is worth the effort.
General-Purpose Image-Processing Software
Even with dedicated imaging programs, many successful astrophotographers still do the finishing touches on their images with standard commercial image-processing software. The industry standard for this is Adobe Photoshop. You will need it eventually, although the cheaper “LE” version will probably be sufficient.
For a free alternative, check out GIMP, which is a GNU foundation image editor quite a bit like Photoshop. It’s less well documented and lacks some of Photoshop’s features, but it’s quite powerful, and it’s free.
Note that most astro-imaging cameras don’t produce JPG files. They produce a specialized file format called FITS, which is a standard in the Astronomy field, but which photography-oriented software such as Photoshop can’t read. So, you will also need a converter or plug-in such as the free “FITS Liberator” application, that converts a FITS file to a TIFF file that Photoshop can read.
Planning and Administration Software
As you grow in sophistication (or if you just like gadgets) you may want to add software that helps with the planning and administration of your activities. There are a wide variety of additional software packages that may assist you; let’s look at a few to give an idea.
Planetarium and Star Chart Software
- planning an observing session before you head outside, getting a general idea of what objects are in what part of the sky;
- looking ahead to see what dates are well-suited for specific imaging targets;
- passing time on the many more cloudy nights you will experience once you take up imaging.
With some of these applications, such as TheSkyX, you can add a photo of the horizon from your own observing site, so you get the sky map drawn in the context of the exact horizon you are dealing with (showing what trees and buildings are in the way, etc.).
More specialized software is available to assist in planning observing targets but that omit the fancy graphics of planetarium programs. AstroPlanner is one example – it can generate a list of targets for your location and a given date, constraining them by type of object, brightness, location in the sky, etc.
Once you have built up a collection of advanced tools, you might want to explore the sophisticated automation software available. Packages such as “CCD AutoPilot” and “ACP Observatory Control” integrate your many other packages to provide a centralized, complete automation service. For example, you can completely automate a sequence such as:
- Open your motorized observatory dome (!)
- Take flat frames against the twilight sky
- Automatically focus using a suitable star near your imaging target
- Automatically centre the imaging target
- Take a sequence of exposures via various filters, refocusing as the temperature changes and between filters, and automatically keeping the dome rotated as the sky moves through the night;
- Automatically image a reference star for colour correction
- Close the dome as dawn approaches
- Detect rain or cloud, and automatically shut down and close up.
If you have equipment of this nature, you’re more sophisticated than I am, and this article has nothing more to suggest for you.
ASCOM: a Standard Hub for Connecting Components
A final special mention goes to a package of software that is not an application and that you will never run directly, yet which may be critically important to you.
The astronomy equipment field has many manufacturers, highly specialized equipment, and few standards. Originally, each equipment manufacturer would release customized software for each product. Each product would work well on its own, but there was no way to connect products from different manufacturers, or even from different product lines from a single manufacturer. Not only did this mean you had to have a large number of software packages, but it prevented you from using a mix of different packages as your preferred environment – each device could be connected to one and only one application at any given time. For example, if you had a manufacturer’s proprietary mount control program connected to your mount, then you could not also connect your planetarium software to your mount at the same time – the device would be willing to connect to only one piece of software.
This is the problem addressed by the ASCOM interface. This is a free, open-source software collaboration that develops and supports “hub” software.
Think of ASCOM as a connector box that sits between your collection of control programs and your collection of equipment.
On one side, ASCOM can look like a generalized piece of Astronomy equipment on your computer, and practically every piece of device-control software (camera control, mount control, etc) has “ASCOM” as one of the devices it can support. On the other side, drivers are available (downloaded separately) that lets ASCOM connect to and control practically every kind of mount, camera, and other device on the market.
This arrangement allows you to run multiple different control programs, all connected to ASCOM, and have them all cooperate in the control of your devices. It’s an elegant solution and works very well.
The next and final topic in our introduction to astrophotography equipment will be a recommendation that you develop and maintain some overall system diagrams in various levels of detail to help you assemble, debug, and reassemble your setup.