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Webcam Astrophotography on the Mac
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The majority of computer users run Windows software, so it is no real surprise that most of the websites that describe webcam astrophotography are written for Windows users. But does that mean Mac users can't participate in this exciting branch of the amateur astronomy hobby? A couple of years ago, and the answer might well have been in the negative, but recently Mac users have seen a surge in the number and quality of the astrophotography tools available to them, and there really is no reason for someone with a portable Mac not to have a go at taking a portrait of Jupiter or the Moon.
A picture of Jupiter with its four largest moons, taken using the iBot webcam and the Astro IIDC image capturing software.
This article is a collection of ideas and observations that are intended to help someone with a Mac get started in webcam astrophotography. While the PC-oriented websites are undoubtedly worth looking at, for Mac users the frequent reference to Windows software can be off-putting. This is unfortunate, and this article is presented here to try and counterbalance this by providing tips on what applications are available and how they can be used. The focus of this article is also firmly on unmodified webcams; not because you can't use modified webcams with Macs, you can, but only because my experience is with unmodified webcams.
What You'll Need
Apart from a Mac running OS X and a telescope of some kind, you'll need a few other bits and pieces before you can get started. The first thing, naturally enough, is a webcam. Webcams sometimes come with only Windows software, but many also have Mac software included, and getting one of these is obviously very convenient. But some of the webcams that work best for astrophotography (like the Philips 'Vesta' series) don't come with Mac software. Fortunately, these will run just fine using third party drivers and image capturing software. The ongoing open-source Macam project is one option, offering free drivers that work with a huge range of USB webcams. If you prefer your software built to commercial standards, then IOXperts offer $20 drivers that work with a both USB and FireWire webcams.
Next you'll need a way to connect the webcam to your telescope. There are lots of ways to do this, but the simplest approach is to remove the lens from the front and replace it with a screw-in adapter. Steven Mogg makes 'Universal Webcam Adapters' for $20 a throw, and these can be ordered online at his website. Make sure to look through his catalogue carefully so that you order the correct one, as not all adapters work in all webcams.
Connecting the webcam to your PowerBook or iBook isn't going to be difficult, as all of the recent models of these come with both FireWire and USB ports. But which is best, FireWire or USB? On paper at least, FireWire trounces USB 1.1 (the standard USB interface on webcams) because it allows a much greater flow of data from the webcam to the computer. This means movies can be recorded with higher resolution, greater frame rates, and less compression, three things that help ensure that no detail is lost. Having said this, many of the very best images taken by amateurs have been done with USB webcams, despite their theoretical shortcomings.
A bit more serious an issue is whether or not the webcam has a 'CMOS' or 'CCD' chip inside it. These are the bits that actually catch the light and turn it into electrical signals, and of the two, CCDs have rather better performance in low light conditions. It's difficult to tell whether or not a webcam has a CCD or not by looking at it, but it should say so on the box, and failing that you may be able to find that information out from the manufacturer. CMOS webcams can still be used for astrophotography though, and I've seen great pictures done using webcams of both sorts.
Image Capture Software
The Equinox planetarium program includes webcam image capturing software built in.
Image capture software is usually included with the webcams sold as Mac-compatible ones, and more often than not the software is some version of BTV Carbon or BTV Pro. Shareware versions of these programs are also available for use with either USB or FireWire webcams, at $20 and $40 respectively. The Pro version has some extra features but nothing all that important for astrophotography, and either will do what we need adequately well.
If you have FireWire webcam, the Astro IIDC program is far superior to even BTV Pro, and well worth looking into. More will be said about that program later in this article. Another alternative, this time for people with USB webcams, is the image capture utility supplied with the Macam drivers mentioned earlier. If you want something a bit more sophisticated, Keith's Astro Imager ($10) offers a few extra features particular to astrophotography that Macam, BTV Carbon, and BTV Pro lack. Yet another option is to capture your images directly from your webcam through the popular shareware planetarium program, Equinox ($39). Like Keith's Image Stacker, Equinox is designed with the amateur astronomer in mind, and has some interesting features like on-screen focusing algorithm, an alignment grid, and on the fly summing and stacking of frames to give, at least approximately, some idea of how much detail is coming through.
The primary task of image capture software is to record the images collected by your webcam and record them to your hard disk as movies. On the Mac, these movies are usually in the QuickTime format, as opposed to the AVI format favoured by Windows users. Neither is intrinsically better than the other for the purposes of astrophotography, but Mac users do need to remember a couple of key things about QuickTime movies. The first is that its usefulness as a medium for recording the detail on objects like planets that occupy only a small region of each frame depends greatly on the compression method used. The second issue is that Windows software, like Registax, cannot read QuickTime files, so if you intend to use to do some of your image processing in Virtual PC (or heaven forbid a real PC!) you will need to convert the QuickTime movie to the AVI format.
Compression and Image Quality
If you are imaging the Moon, the default compression settings will probably
be fine, at least to begin with, but if you want to photography the planets,
then you will almost certainly need to change the webcam video settings.
This is normally done through your image capture software; in BTV Carbon
and BTV Pro choose the 'Video Settings' options under the Settings menu.
By default, QuickTime 6 comes with lots of different compression modes,
known as 'codecs'. These compression modes are sometimes described as being
either 'lossy' or 'lossless' depending on whether or not they throw away
data. Since we are interested in maintaining all of the information that
the webcam collects about colour, contrast, and brightness, lossless compression
modes are preferable. The downside to this is that lossless compression
modes produce larger QuickTime movies than lossy ones because they are
storing more information.
BTV Pro, and most of the other webcam image capturing programs that use QuickTime, offer a wide variety of compression modes so that you can get the most data into the smallest files.
You also have the option of not using any compression at all (by switching the compression setting to 'none'). Although you know that everything is being recorded, not using any compression at all does result in simply huge files, several hundreds of megabytes in size for thirty seconds of 640 by 480 footage. If you happen to have a laptop with a few gigabytes of space, then this is often the easiest way to go, but otherwise using one of the lossless compression modes is much more efficient.
Unfortunately, the QuickTime documentation doesn't tell you which codecs are lossy and which ones are lossless. You can find this out on the Web easily enough, and it is also in the BTV documentation as well. In fact you really don't need to know this information so long as you avoid any of the codecs designed for animations or use with slow computers and network connections. These include the Animation, BMP, Cinepak, Graphics, H.261, H.263, and Photo JPEG, none of which is really much use for astrophotography. Much better choices are the codecs meant for high-quality video, such as Component Video, the various DV codecs, MPEG-4, and Sorenson. Any of these should work well, but there are differences between each that means that you will need to do some experimentation do find out the best for your webcam and whatever it is your are trying to photograph. In general, both MPEG-4 and Sorenson are good all-rounders, and probably the best ones to start out with.
As an alternative to buying or using webcam drivers and image capturing software designed for applications other than astrophotography, why not get some software made expressly for the task? Astro IIDC ($50) is designed for use with FireWire webcams and cannot be used with USB ones, which limits the range of webcams it can be used with. But this minor limitation is more than compensated for by the variety of astronomy-specific features it offers. Among other things, Astro IIDC allows you to do long exposure shots without needing to modify the webcam in any way. These long exposures are limited to slightly over one second, but this is plenty of time to capture detail on the planets that wouldn't otherwise have been possible in each frame, making stacking and processing much more effective.
Astro IIDC doesn't use the QuickTime codecs or third party driver software,
instead communicating directly to the webcam and compressing video using
a proprietary format designed specifically for scientific imaging. A copy
of this codec is installed on the Mac to allow you to play back movies
using standard Macintosh software (such as the QuickTime Movie Player)
but otherwise the program is completely self-contained.
Astro IIDC includes lots of features useful for amateur astronomers, such as true control of exposure length, up to a maximum of one second.
How does running Astro IIDC alongside a telescope feel different to using a standard image-capturing program? The first thing you'll notice is that you can more easily change things like the brightness and gamma on the fly. This is useful because the settings that will work well on a bright, contrasty object like the Moon aren't the best ones to use on Saturn or Jupiter with their more subtle details. Colour balance is important too, and you can either allow Astro IIDC to correct for this automatically (which won't always be effective) or use the sliders to adjust the red and blue gain.
You also get to change the exposure length. While the other webcam image capture programs do allow you to alter the number of frames recorded per second, all this does is increase the interval between each exposure. The exposures themselves don't increase in length, and stay at about one-thirtieth of a second. In contrast, Astro IIDC allows the use to increase the frame length as well as the number of frames recorded per second. Obviously, the longer the exposure, the fewer you can record per second, so that when the camera is set to the maximum exposure length, focusing becomes more difficult because the image you see on the screen is updated only once per second.
Processing the Image
Once you have the images recorded to your hard drive, the work of processing begins. There are three main steps here, aligning the individual frames to compensate for things like vibrations in the telescope's mount; stacking the frames to create a single composite with enhanced detail; and finally using various graphical sleights of hand to improve the final image.
No fewer than three Mac OS X programs exist that will allow you to do all of these things within a single application: Keith's Image Stacker, Lynkeos, and AstroStack. Keith's Image Stacker ($10) has been around for several years and is probably the most widely used astrophotography program on the Mac. It uses a highly graphical interface, comes with lots of image enhancement tools including unsharp masking and colour adjustment tools, and imports QuickTime movies directly.
Lynkeos (open source freeware) is a more recent addition to the Mac scene, and offers a simpler alternative to Keith's Image Stacker. While easier to use, it does lack many of the advanced tools for image enhancements that Keith's Image Stacker offers. So while it can be used as a standalone application, it works even better when used with a graphics program like Photoshop.
AstroStack has been popular among Windows users for years, and is now available in a Mac version.
The third option is AstroStack (free in its 'limited edition' form, otherwise $59). AstroStack has been around for years on the PC, but now exists in Linux and Mac OS X versions as well. Compared with Lynkeos, it's a complex program, and unlike Keith's Image Stacker, it doesn't work with QuickTime movies directly. Instead, you'll need a program capable of extracting frames from QuickTime movies and saving them as individual BMP, GIF, JPEG, or PNG files. There are various applications capable of doing this, but GraphicConverter ($30) is a particularly good choice because it can also be used as a graphics editor for the later stages of image enhancement as well. If you already have QuickTime Pro ($30) installed on your Mac, you can also use this to convert a movie to a set of individual frames, using the Export command and choosing the option to save the files to an Image Sequence. While doing this, you'll be given various graphical format options to save the images as; in general, PNG files are probably the best ones to go for, having the best balance between size and image quality.
GraphicConverter is a useful program for any Mac users (and comes as part of the software bundle on some Mac models). Of prime importance to users of AstroStack is its ability to create a stack of images from a QuickTime movie in any format you want.
A fourth program is on the way to becoming yet another option for the Mac-using astrophotographer, and that is AstroYacker (freeware). Currently its most important application is as a fix for the problem with alt-azimuthally mounted telescopes, their inability to compensate for the slow rotation of the target as it moves across the sky. A few other errors are corrected as well, and the movie is also cropped down to a region of interest so that subsequent editing can be carried out much more quickly. In time, the writer of the program intends to add on features building AstroYacker into a highly graphical, QuickTime-savvy, image stacker and editor. While not there, this is certainly one to watch.
Registax on Virtual PC
Though running PC software on a Mac is anathema to some, there's no question that it does offer you some extra tools, such as Registax, that can be very helpful.
There are two popular webcam image stackers and processors on the Windows platform, AstroStack and Registax. AstroStack exists in Macintosh and Linux versions as well, but Registax is a Windows only application. Even a cursory survey of the astrophotography galleries on the Web will reveal that Registax is widely used and highly effective. Luckily for Mac users, Registax runs very well in Virtual PC ($229 with Windows XP Home Edition included).
One of the nice things with Registax is that it comes with very detailed help files and instructions, so that even a new user can get to grips with this program very quickly. It includes several tools for simplifying the frame selection process by using mathematical analyses to separate the sharp, contrasty frames from the poor ones. While any of the Mac programs will allow you to select frames, stack them, and then enhance them, getting really good images seems to be just a tiny bit easier in Registax than any of the other programs around.
The only thing Mac users need to worry about when using Registax in Virtual PC is that Registax works with AVI files, not QuickTime movies. Converting between the two is easy in QuickTime Pro (choose the Export command) and set the compression codec to 'None'. While you can copy the AVI file across to the Windows desktop in Virtual PC, it is much faster to simply move the AVI file to a shared folder. Virtual PC allows most programs to read and write to shared folders on your Mac hard drive just fine. Once you are finished working with Registax, you can save the image file to the same shared folder for further editing in your Mac OS graphics program or uploading to your web page.
Final Image Editing
While AstroStack and the other image processors described here all have tools for enhancing the final image and saving it in a format suitable for posting on web pages or printing, most users will prefer to do these final steps in a traditional graphics application. Photoshop is of course one option, but this is a big, expensive application that is overkill for the needs of the Mac-using amateur astronomer. Costing precisely nothing but the time it takes to download, MacGIMP is a great alternative. It runs in the X11 environment within OS X users, so has a somewhat different look and feel to Aqua applications, but it does contain all the tools that we need to tweak our images.
The main things you'll need to do are 'unsharp masking' and 'Gaussian
blurring', the first makes the detail more obvious, and the second smudges
away overly-artificial looking spots and blotches that sometimes follow
the image enhancement process. In MacGIMP, you'll find these two tools
under the Filters menu item (control-clicking the image should make them
available, too). You will probably also need to adjust the colour balance
and brightness of the image. The Curves and Levels tools are especially
useful for this sort of thing, and these are in the in the Colour Tools
subsection of the Tools menu item (again, control-clicking will bring these
MacGIMP is free but very powerful, and gives you access to all the filters and image enhancement tools you're likely to need.
There really aren't any optimal settings for the sliders that control all these adjustments and filters. Instead, you'll need to experiment to find out what works best for you, and this is going to vary with each image you do. The main thing is to work on a copy of the original image file, so that if you mess it up you can always discard it and start again. Once you're done, you can export the image as a JPEG for posting on a website, but if you can, check the image out on a Windows PC beforehand. Windows and Mac computers have slightly different 'gamma' settings; essentially the overall brightness of the screen, and sometimes images that look fine on a Mac can be very dim on a PC.
What Went Wrong?
Before wrapping up this article, it's worth making a quick diversion into the other factors that affect webcam astrophotography beyond the software. Lots of people take images, find that even their best shots are a bit small or blurry, and having seen some of the spectacular images on other people's web sites get disillusioned with the whole thing and give up. This is a shame; like any other artistic endeavour, practice is absolutely central.
So what are the factors that are important when recording movies of the Moon or planets? Top of the list is seeing conditions. While sky darkness doesn't matter, and even transparency isn't all that important, if the atmosphere isn't steady, then all the stacking and processing in the world isn't going to bring out details that were blurry before they even hit the webcam. Visual observing is a good way to estimate the seeing conditions, and what you want is for your view of Jupiter or Saturn to be crisp and sharp at a magnification of 200 or more. This isn't to say you can't do some imaging when the sky isn't that steady, you can, it's just that your maximum magnification is going to be limited, and therefore the amount of detail you can capture will be relatively low. On nights of poor seeing, you're probably best imaging Moon, where high magnification isn't essential.
Next on the list of potential problems is your telescope. Collimation of reflecting telescopes is absolutely essential. SCTs in particular seem very sensitive to poor collimation errors at high magnifications. Even if the collimation is spot-on, if the telescope hasn't cooled down enough, then air movement within the optical tube can mess up your images. Tracking can be an issue, particularly if you are recording images of the planets, but even basic go-to telescopes should track acceptably well for our purposes. Heavy-duty equatorial mounts, or alt-azimuthal mounts with field de-rotators, are obviously better, but they certainly are not essential.
Barlow lenses and star diagonals are less critical but still significant.
Most of the best photographs of the planets are taken with telescopes running
at f/30 or even more. This corresponds to using a x3 Barlow lens with a
standard 200 mm SCT, resulting in magnifications significantly above those
we normal observe visually with. If you only have a x2 Barlow lens, or
a 'fast' telescope like a wide-field refractor, then you are going to be
limited in the magnifications you can achieve. Low magnifications mean
that the image from the telescope is cast on only a small proportion of
the CCD chip inside the webcam, which reduces the resolution and thus the
amount of detail it is possible to capture. Star diagonals are another
weak link in the chain, and ideally you want to avoid using them. Cheap
star diagonals (which includes most of 1.25-inch models that come with
go-to telescopes) tend to scatter the light, particularly when they are
dirty or dusty, and this degrades the quality of the image.
It's well worth going back to old QuickTime movies and unprocessed images to try out different approaches using your aligning, stacking, and editing software.
Most of these issues can be avoided or worked around, so none is fatal, and none has anything to do with your computer. Even once you've recorded and processed your movies, there's nothing wrong with coming back to them again later and processing them again. I've found subtle differences in the way each program works, and sometimes I find one program works best and other times another. Similarly, trying out different settings on the unsharp masking and Gaussian blurring filters can have huge effects, and as you get more experienced with all of these tools, you'll find yourself able to bring detail out of old QuickTime movies you missed before. Patience and practice should be your watchwords, and if you feel the images you obtained weren't that great, try and figure out what went wrong.
I took this shot of Saturn from an urban garden using an SCT that wasn't properly collimated and running at only f/20, and on a night of average seeing to boot. If I can do it, so can you.
Mac users have a terrific range of software and hardware suitable for webcam astrophotography at their disposal. A basic set-up needn't cost very much, essentially the cost of the webcam is the only essential expense.
- Webcam -- $50 or so for a basic USB model
- Webcam adapter -- make your own
- Drivers -- included with the webcam, or use Macam drivers
- Image capturing software -- included with the webcam, or use the Macam software
- Aligning and stacking software -- Lynkeos (free)
- Image processing software -- MacGIMP (free)
- Webcam -- $100 for something like the Fire-i or iBot
- Webcam adapter -- Steven Mogg adapter ($20)
- Drivers -- Unnecessary with Astro IIDC
- Image capturing software -- Astro IIDC ($49)
- Aligning and stacking software -- Keith's Image Stacker ($10) or AstroStack Pro ($59, plus a utility for converting movies to a sequence of images)
- Image processing software -- MacGIMP (free)
Neale Monks is author of Astronomy with a Home Computer, a book written for Windows, Mac, and Linux users alike and part of Patrick Moore's 'Practical Astronomy' series. He regularly writes astronomy software reviews for AppleLust, has created a couple of trivial little astronomy programs, and keeps as small gallery of his own astrophotography work online, at: