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
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
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
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.
More advanced or ambitious hobbyists can spend a bit more, opting for faster
FireWire webcams and software expressly designed for their needs, such
as Astro IIDC.
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
Aligning and stacking software -- Lynkeos (free)
Image processing software -- MacGIMP (free)
So, even a dream set-up comes in at less that $180, of which the lion's
share of the cost is the webcam itself, and a lot less than the cost of
a single premium eyepiece. Of course there's more to astrophotography with
a webcam than what operating system you use, and the specific techniques
and skills general to both Mac and Windows users fall outside the scope
of this article. But what I hope to have made clear here is that simply
because most of the webcam astrophotography websites are done by Windows
users, doesn't mean that Mac users can't enjoy this part of the hobby.
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: