Twenty-five years ago I abandoned astronomy to pursue
other interests. Today, I return to the hobby and discover a booming field
ripe with technological
innovation. The bad news is that everything I knew has to be learned again,
the good news is that the sky is full of rewards that were unthinkable
a quarter of century ago. This beginner's guide is not intended as a dazzling
of good astrophotography but rather as a mundane account of my new adventures
in astro-photography, complete with mistakes and growing pains. Amateur
is one of the few areas where the internet has lived up to its hype: a
staggering amount of free information is available on-line, shared by an enthusiastic
and talented community: this article is my way to thank all those who have
contributed knowledge, hardware tips and great software.. Clear skies to
Analog or Digital? Decision Time
The amateur on a budget has
three astrophotography options: digital cameras, web cams or , conventional
photography. These choices are not mutually
exclusive and, if you already own a digital camera, it is quite possible
both digicam and web cam photography for less than $500. In fact, this
is the path
I chose for my own investigations. Let's first examine the possible choices:
Having worked with conventional photography
in my early days, I advise you to ignore that route today. While great images
can still be obtained on
film, if you have no experience, conventional astrophotography could be frustrating:
focusing is hard, exposure somewhat random and, even in the days of 30
mini labs, the delay between the shoots and the results can be agonizing.
Believe it or not, digital images produced by today's amateurs are often
what major observatories published in the 70s. Also the experience gained
in conventional astrophotography will be lost if you choose to push your
further in the future. If that wasn't enough, conventional photography
is also the most expensive choice in the long run.
Digicams take acceptable single shots (Olympus 2100 UZ, Scopetronix Adapter,
no processing) but the setup can be extremely bulky
Digital Cameras are hot! One can find excellent
second hand digicams such as the members of the Nikon 99x family (or even
the more recent 4500)
for a little
less than $500 and still coerce an afocal adapter in the budget. The
strong points of digital cameras are their high resolution, good quality
different zoom levels, good color sensitivity, good single shot abilities
and, in some models, good long exposure (bulb) abilities. However,
are not perfect: paired with an eyepiece, they often suffer from vignetting.
Their weight and bulk can stress your mount. They will definitely affect
its pointing accuracy. Vibrations will force you to use delayed or
You don't want to drop that gun on your toes!
Unless you shoot in RAW or TIFF mode, the jpeg compression algorithm
will actually work against further digital processing. Working in
RAW or TIFF mode carries an additional price: it is relatively slow and its
will increase the cost of your imaging system. Don't forget that
quality may, in theory, suffer a bit since the diagram lenses are
often made of several
lenses: when one adds the two or three optical interfaces of the
scope to the several lenses of the eyepiece and of the camera, one can quickly
of interfaces. Finally, digital cameras do not defy Newton Laws:
drags them to the ground, action-reaction breaks them apart! While
this may sound
like a joke, this isn't. Look at the size and bulk of a typical setup
and imagine that thing hooked to your focuser, in the dark...
said, Digital Photography is an extremely fast moving area and a very credible
imaging choice: if you have a relatively large
budget, a Canon
D60 on rock solid mount is an outstanding tool. It's likely to
get better and cheaper tomorrow, why not wait a bit?
web cams are small and light
At first, with their low resolution (typically 640 by 480) and low
image quality, web cams seem an unlikely candidate for astrophotography. Looks
can be deceiving:
amateurs with 10 to 12 inches telescopes routinely use web cams to obtain planetary
images that surpass what analog photography and very large telescopes could
achieve in the 70s. Because of their acquisition speed, web cams are able to
take advantage of the fleeting instants of good seeing that conventional photographers
will miss. Since seeing is the limiting factor as far as planetary imaging
is concerned and since planetary imaging is a very important part of what the
amateur on a budget can do, a web cam is the ideal partner for the budget minded
astrophotographer. They are also the cheapest ($120 gets you a conventional/deep
sky dual mode camera and an adapter), do no suffer from vignetting and do not
stress the telescope mounts or focuser. Since they are software controlled
and have no shutter or curtain, vibrations are a non issue (it helps not to
trip on the USB cable). They feed streams of uncompressed BMPs into AVI movies
upon which image processing can work its magic. They introduce the novice to
the basic techniques of image acquisition and image processing that have become
the backbone of today's digital astronomy: the knowledge gained from their
use will not be lost should you one day move to "real" astronomical
Web cams are not perfect though. The right web cam can be hard to find
in the US, unassisted focusing can be tedious, their field of view is small,
color accuracy isn't great. Last but not least, they easily get dirty. However,
since these shortcomings are either unimportant for the amateur on a budget
or since work-around do exist, I believe web cam astrophotography is the
way to go.
Here is a summary of the different imaging opportunities open to the amateur
on a budget
||good to excellent
||extremely hard, delayed results
|field of view
||small (can be a +)
||some, eventually a lot
||heavy (lever effect)
||from medium to extremely heavy
||some, requires remote or timer
||a lot, requires masking
||extremely easy and rewarding
||quick (save & download time)
|tools and techniques
||many available free, lots of information
||lab material harder and harder to find
||$150 - less than $500 gets you cooled results
||from $600 up to several thousands
||from $50 to several thousands
||approx $15 per film roll, batteries.
||cheap plastic adapter works well
||wide field eyepieces, strong connections
||standard adapters for most cameras
||easy with cheap cable up to six meters
|| fall, cheap mount's brake could slip or break
||same as digital
||one, the scope
||up to ten lens interfaces
||from none to many
Choosing a web cam
The Philips ToUCam Pro (or Vesta Pro) also known as the 740K
or the "egg" has
become the de facto standard for amateur astronomy. It is based on a Sony ICX098BQ
CCD chip that is both very sensitive to light and of relatively high quality.
Be especially careful not to choose the non pro version, also known as 730K
as it uses a CMOS sensor that is roughly ten times less sensitive to light
and therefore less suited to astronomical use. The objective of the camera
has to be removed and an adapter is required to align the camera into the focuser.
While this is an area where you can save and recycle old film cans to build
a home made adapter, I suggest that you do not: alignment is too important.
A hardware guru called Steve Chambers found a way to modify the design of a
typical web cam to allow longer exposures, suited to deep sky imaging. Should
you get such a Deep Sky capable web cam? That mostly depends on the precision
of your telescope mount, but I would recommend that you go for the modified
web cam since the price difference is relatively small. Besides, you will only
know how your mount tracks after you have tried it. If you can not find a ToUCam,
Molyneaux's site: it offers valuable information about web cams
and their suitability to astro-photography.
The Toucam and its adapter (left) The eye of the "egg" - yes,
it's dirty (right)
Don't forget to install the camera software drivers before going
out! It is also a good idea to become familiar with its control panel as
it has some quirks
that could disorient you during your first session. You will also need software
to acquire the images: there is a truckload of them, most of them freeware.
I personally have settled on a program called K3CCD Tools by Peter Katreniak,
but this is simply a matter of preference since most programs use the same
method to acquire images.
K3 CCD Tools is one of the many freeware available to acquire astronomical
images from a web cam It even does support the long exposure modification.
Your pre-flight checklist should looks like
- is the camera connected and recognized?
- is the resolution chosen?
- is a default directory defined for the night's
- is there enough disk space?
- is the default naming convention chosen?
- is the default acquisition speed
- Quiz: what can you say about the picture on the left? (see answer
started - the acquisition phase.
If you have an equatorial mount, your telescope
will be polar aligned. It will also have cooled down. With astrophotography,
more than ever, having
properly polar aligned makes your life easier. Having the scope cooled
down makes sure you'll get the best images possible: if you are using a
MAK design, allow 2-3 hours of cooling before beginning your session.
Our first target will be the Moon. Use a low power eyepiece to center
the moon, then a high power eyepiece to select a zone of interest. Once
remove the eyepiece, insert the web cam and focus. Bingo, that's all
there is to it: on the Moon, the web cam is usually able to use auto-exposure
to obtain decent images. Your first images of the Moon could look like
image. Not too bad, for a first try.
first light on the moon
The Planets: Jupiter, Saturn
Imaging the planets is trickier though. The first
problem is to put the planet in the limited field of the web cam: use a low
power eyepiece, center the planet,
then use a high power eyepiece for fine positioning. When the target is perfectly
centered, replace the eyepiece with the web cam The second problem is to
focus the planet while keeping it in the field of view: if you have a telescope
focus shifts the mirror a bit and whose drive backlash is capricious, this
simple operation can be frustrating: be patient, we'll soon revisit the focus
The third problem is to keep the planet on the CCD: if you have a
motorized mount, make sure it is tracking accurately; if you have a manual
mount, make sure fine movement in Right Ascension is enough to keep the
planet centered. If you have a manual azimutal mount, imaging is still possible
but so tricky and time consuming that I would probably despair. If you can
you have my admiration. The fourth and last problem is setting the correct
exposure. If you are coming from the Moon to Jupiter, chances are that
Jovian monster will be grossly over-exposed - here is my very first Jupiter
picture. Hardly satisfactory, however, the satellites are there!
Fine tuning the exposure and focus
In order to improve the image, we'll have
to put the camera out of full automatic exposure mode image controls to
access the camera control panel and set the
gain to its lowest value. Gain acts like a booster on the sensitivity of
the camera at the expense of increased noise levels.: The lower you can keep
gain, the better the image will be
On Jupiter, setting the gain to its lowest value, the frame rate to 10, the
white balance to outdoor usually yields acceptable results. The frame rate
of ten images per second is a good compromise between image quality and atmospheric
turbulence. Don't be afraid to experiment a bit! Saturn may require a bit
of boosting. Whatever you do, do not overexpose your pictures. Overexposed
areas are saturated at 100% level and there is no technology in the world
that can extract information from such a signal, regardless of the number
of frames available. Under-exposing pictures is not nearly as bad since stacking
and eventual complex analysis can extract meaningful data from multiple exposures.
single avi frames, unprocessed.
Depending on your telescope, you'll easily get results like the ones above.
Now, this is much better! Can we improve on that?
The impact of the seeing
One critical factor in astronomy is called the seeing.Consider,
for example, this single frame of Jupiter: even though it is slightly underexposed
grainy it is much better than the one above: rather than two dull bands
it show three
bands and a faint GRS. The telescope and operator haven't changed, that
atmosphere has! In fact, the above pictures of Saturn and Jupiter were taken
days and the seeing was much better for Saturn. The seeing does matter
a lot! If you think you have done your best and you are not getting good
do not despair and try again another night.
single avi frame, unprocessed, good seeing.
Focusing, gamble or science?
Reaching the perfect focus can be hard, especially
when one knows the enormous impact a slightly missed focus can have on
the resolution of the final image.
While it is possible to reach decent focus on Jupiter thanks to its satellites
(push the gain and focus until the satellites are as small as possible) or
on Saturn (if Cassini is visible, then the focus is about right) it can be
impossible on stars. A very cheap tool can help you focus better: the Hartmann
mask. The mask is basically an objective cap with holes (2, 3, 4) that you
put on the scope. Select a reasonably bright star, center it and try to focus:
as long as you are not in focus, you'll see 2 (2 or 3 or 4) images converging.
Merge them and you have reached the Holy Grail of perfect focus. (Hartmann
masks were invented in the early 17th century by a certain Scheiner, a two
holes Hartmann mask should be called a Scheiner mask)
a standard web cam, a home made Scheiner mask and a modified "deep sky
capable" web cam
How much power is enough?
In astronomy, greed is not rewarded. Those who jump
for the highest magnification will not necessarily get more details. While
this is obvious to any visual
observer who tries to push his scope beyond its ability, the matter is less
obvious with astro-photography where one feels that something can always be
improved. Unsatisfied with the images I was getting with my Celestron Ultima
2x Barlow lens, I made the mistake of buying a TeleVue PowerMate 3x. Of course,
the images became even worse! The reason is simple: both with the Celestron
and with the TeleVue, I was pushing my equipment far beyond its resolving power!
The table on the right shows a "back of the envelope" estimate of
the ideal barlow given a defined web cam and optical instrument. It should
be taken with a grain of salt since the Rayleigh criterion (one of several
method to estimate the resolving power of an instrument of a certain diameter)
can be used to demonstrate that the Cassini division should not be visible
in instruments where it definitely is visible.. Nonetheless gives a useful
ballpark figure - a 3x Barlow on an ETX-125 is definitely too much.
Where diameter, focal length and F/D are obvious, Rayleigh is the theoretical
resolution of the optic, ideal is the ideal sampling rate according to Nyquist
(basically half the Rayleigh criterion), pixel is the number of arc seconds
per pixel on a ToUCAM at 5.6 micron per pixel with the default F/D and Barlow
is the hypothetical Barlow lens needed to achieve ideal sampling. (Note:
the Sparrow criterion seems to be better than the Rayleigh criterion)
In the good old days, cloudy nights allowed the amateur astronomer
to maintain a plausible social life.. then came image processing! Today,
it is not uncommon
to see amateurs devoting more time to their image processing than to their
observing sessions! What is the hype all about?
raw Saturn frame.
Digital image processing is
a set of extremely powerful enhancement techniques that can be used to improve
the appearance and actual resolution of your
pictures, but before examining in in more details, let's remember that.
processing does not beat fine focus.
- image processing does not beat proper
- image processing, just like statistics, can tell any lie.
This being said,
image processing is what makes web cam astronomy so rewarding! Since it is
as much an art as it is a science, it is also a lot of fun to
explore and to invent ones own cooking recipes. Again, many freeware programs
are available. In my opinion, Registax (by Cor Berrevoets) offers the best
lunar and planetary results in a very easy to use package. Registax combines
three enhancement methods;
several 5 seconds AVIs of Saturn, stacked and processed in Registax
Image selection if you watch your avis frame by
frame, you will notice that while some of the frames are sharp, others are
fuzzy: this mostly reflects
atmospheric turbulence. Registax offers both an automated and manual way
of selecting the best frames.
stacking of 100 frames and wavelet transform
Stacking is the least controversial image enhancement
technique. Its goal is to average the information contained in a large number
of frames to increase
the signal to noise ratio. While the details can be subtle (sum stacking
vs median stacking for example) the principle of operation is easy to understand:
noise , random in nature, cancels itself while the signal is proportionally
This Jupiter shows a fair amount of actual detail, but is also clearly over
processed. The red circle artifact is not a processing artifact but an operator
error at capture time.
Wavelet transforms detect edges in images. Adding those edges
to the summed image literally extracts and emphasizes the details it contains.
One of the
big advantages of the wavelet transforms is that they allow the user to select
the size of the features he wants to extract: Registax supports several processing
scales: level 1, 2 and possibly 3 are the most useful for planetary imaging.
Image processing raises some ethical questions: is an image resized, sharpened
and re-colored in Photoshop closer to reality than it is to a plain
drawing? Must Jupiter Great Red Spot absolutely be red when it is not in
reality? The "correct" answer probably does not exist.
The Cassini-Eudoxus region, processed in Registax.
And what about the deep sky?
You may have noticed that even though a "deep
sky capable" web cam
was used in this tutorial, very little has been said about Deep Sky imaging.
The reason is very simple: it is extremely hard to get good deep sky results
with cheap telescope mounts. While I am sure I can turbo-charge and fine tune
my ETX-125's drives to obtain some results, I also know that I am ultimately
doomed by its staggering periodic error. One possible strategy to work around
a poorly driven equatorial mount is to blindly and automatically take a set
of exposures and select the ones that are not blurred because they were shot
during windows of precise tracking.
Nice stars in Praesepe pictured when testing the Hartman mask. The odd shape
is due to tracking errors. I liked the color difference!
Wrapping it up..
That's all folks... now you probably have enough information
to answer the Quiz: the picture of Saturn in K3CCD Tools can't be a single
frame. It is
way too sharp and well defined. It has simply been pasted in the K3CCD
for aesthetic purposes.. I hope this article will help you define your
path in the rich universe of astro-photography.