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The Inexpensive Digital
Revolution
Essay by
By Peter Caspari
Instructor
Melissa Hulbert
HET609
Swinburne Astronomy Online
“All of the work contained in this essay is my own original work unless otherwise clearly stated and referenced”
Introduction
There have been remarkable advances in digital
photography over the past few years. Almost everyone
now has a digital camera whether it be a stand alone
device or a feature of a mobile phone. Photographic
film is disappearing.
This technology has also prompted a revolution in
observing methods for amateur astronomers.
Digital imaging has brought capabilities within the
reach of amateur astronomers that were previously
available only to professional astronomers.
Excellent images of astronomical objects have become
common place in astronomy magazines and websites
and many of these are produced by amateur
astronomers working within very reasonable budget.
Let us examine some of the inexpensive digital camera
options and their remarkable performance now
available to the amateur astronomer.
Webcams
A webcam is a video capturing device originally
intended for use with personal computers.
It wasn't long before these humble and inexpensive
cameras were pointed at the night sky with remarkable
results.
Figure 2. Lunar Image taken with a Logitech
QuickCam Express with a CMOS detection chip.
The above image was taken with a Logitech Quick
Cam express which has a CMOS detection chip. The
telescope used was a 4.5” Newtonian without tracking
facilities. This image is a mosaic of many images.
To modify a webcam for basic astronomical use is
relatively straight forward. Adapters can be purchased
that replace the existing lens and allow the camera to be
put in a standard 1.25" telescope focuser tube. An even
more inexpensive alternative is with the use of a 35mm
film canister. This film canister can be modified with a
pair of scissors and attached to the camera with super
glue. This will also allow it to fit perfectly in a
standard 1.25" telescope focuser tube.
Figure 1 – A Logitech Quickcam Pro 3000 webcam
These cameras can have a CMOS or CCD detection
chip. The ideal detection chip is a CCD however even
CMOS detection chip cameras can produce excellent
lunar images.
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Basic Overview of Image Processing
To get the high quality images achievable from a
webcam a process called image stacking is required.
This remarkable process combines many individual
images into a single image. The movie file captured by
the webcam can be loaded into a software application
which makes this stacking process relatively straight
forward. An example of such an application is
Registax (Regiweb) which is very capable at this task
and is also free.
This image can then be further enhanced to sharpen the
image and bring out the detail. This can be done by
any of a number of graphics packages such as
Photoshop.
Figure 3 – A Logitech Quickcam with Mogg adapter.
www.moggadapters.com
The limitation of these cameras in this standard
configuration is that they are only capable of short
exposure times limiting them to the Moon and bright
planets. Some webcams have also been successful
used to image deep sky objects.
Any basic webcam capture software can capture a
movie file that can then be processed by freely
available software to produce remarkable images.
For planetary imaging, the small apparent size of the
target often requires the use of a Barlow lens which
effectively enlarges the image.
Figure 5. Saturn before and after processing
Long Exposure Webcam Modifications
As discussed earlier the limitation of standard webcams
is that they are only capable of short exposure times
limiting them to bright objects such as the Moon and
bright planets.
Modifying them for longer exposures allows more
photons to be collected by the CCD detector. This
allows for imaging of fainter objects such as nebula and
galaxies.
Figure 4. Image of Jupiter plus its moon Europa
casting a shadow on the planet.
Perhaps the best known pioneer in modifying webcams
for use in astro work has been Steve Chambers who
developed what is now called the SC mods (SCweb).
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These modifications require some basic electronics
skills and may not be for everyone. However the
images produced are excellent considering the low
costs involved.
Modified Surveillance Cameras
Modified webcams, while powerful and capable of
produce stunning images, do not have the sensitivity of
the high end purpose built CCD cameras. This
sensitivity is need to image very dim objects.
A list of webcams, their sensitivity and options as far as
long exposure modifications is available on Dave
Molyneaux website (DMweb).
For those who want to chase “dim and fuzzies” a low
light surveillance camera can be modified in a similar
way to the long exposure webcams. This setup can
produce a camera with remarkable sensitivity.
When you start work with long exposure images
background noise becomes an issue which adds some
complexity to the image processing. A method of
reducing the background noise is to cool the CCD chip
and some amateurs have successfully done this but its a
complex modification.
Jon Grove developed the long exposure modification
for the 1004X low light surveillance camera (JCweb).
It requires some significant modifications similar to
webcam long exposure modifications however the end
result is a very sensitive monochrome camera.
Some of the background noise can be subtracted from
the image with the use of “Dark” and “Flat” images.
Dark images contain hot pixels that are faulty pixels
common in CCD chips. Flat images contain a
background that often has some inconsistency. These
images are subtracted from the actual image to reduce
the noise introduced by longer exposures.
Otherwise the image processing techniques are
basically the same for the unmodified webcams.
Figure 7. M51 with Modified Surveillance camera
(http://www.geocities.com/jgroveuk/Galaxies.html)
Entry Level CCD cameras
If the modifications involved with webcams are not
suitable there is a range of camera on the market that
offer similar and better performance such as the Meade
DSI range of camera. While more expensive than
webcams these cameras have remarkable performance
and are reasonably priced (Meadeweb).
Figure 6. M42 and M43
Long exposure modified Logitech Quickcam Pro 3000
(http://keithwiley.com/astroPhotography/images.shtml)
Using these cameras is usually easier than webcams
especially the modified variety however their
sensitivity still does not match the purpose built
medium to high end astro camera such as an those
available from SBIG (SBIGweb)
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One of the most sensitive entry level CCD cameras that
have been on the market was the SAC Imaging SAC8II. This camera is basically the modified surveillance
camera discussed above with peltier cooling packaged
into a commercially available product.
This camera has many limitations such as only being an
8-bit monochrome camera with low resolution.
However it has exceptional sensitivity and can image
very faint objects with relatively short exposures. Its
quantum efficiency is comparable to many medium and
high end CCD cameras.
The sensitivity of such cameras makes them suitable
for more scientific purposes such as astrometrics and
photometrics in addition to astrophotography. The
SAC 8-II with an 8” Newtonian can approach
magnitude 20 in moderately light polluted skies
(SAOProjweb).
Figure 9: This spectrum was created from an image
taken with a SAC-8II and a Star Analyser diffraction
grating
An example of what can be done with a diffraction
grating such as a star analyser (SAweb) and an
inexpensive camera is calculating the redshift of
Quasars. The redshift of Quasar 3C273 was calculated
by comparing the emission lines of Hydrogen.
This configuration has also been used for photometry
and can produce light curves on objects as dim as
Magnitude 14.
While achieving scientific results with such a camera
may requires more image processing than a medium to
high end CCD the cost saving is dramatic.
In this case, Quasar 3C 273 had its Hydrogen Beta line,
Hb, (normally 4861.33 Angstroms) shifted to 5679
Angstroms. From this shift a redshift of z = 0.1542 was
calculated which is close to the expected z = 0.158339.
Spectral Analysis
Another powerful use for the types of cameras
discussed is spectrum analysis. This is something
previously only available to the professional
astronomer now available to amateur astronomers on a
very reasonable budget.
Spectrum analysis is a scientific method of charting and
analyzing the chemical properties of matter and gases
by looking at the bands in their optical spectrum. This
can be done by mounting a diffraction grating in front
of the camera. The spectrum is then spread across the
image. The image can then be analysed with a
software package such as Visual Spec (VSweb).
Figure 8: This image was taken using a Star Analyser
diffraction grating and a Philips ToUcam Pro webcam.
(http://www.patonhawksley.co.uk/gallery.html)
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(SBIGweb) which may only offer a marginal
improvement in limiting magnitude.
Bringing it together
BDI Observatory, located 25 km south of Sydney
Australia, and is an example of how this technology
can be utilized.
The primary limitation with the SAC 8II is that it is
only an 8 bit camera however the work around for this
is to take many short exposure images and stack them.
As a result literally thousands of images are taken
during a typical observing session and these images
need to be stacked in to a manageable set of images.
Most stacking software requires manual selection of an
alignment area which would be cumbersome however
DeepSkyStacker (DSSweb) does not and it can be
driven from other software application which can
automate the entire stacking process.
This is an example of some of the additional tinkering
that may be involved in working with a low end budget
camera however the resulting images are of a high
enough quality for astrometric and photometric use.
This configuration is being used to do follow up
astrometric asteroid observations for the Minor Planet
Center (MPCweb). Before these types of observations
can be submitted the Minor Planet Center requires a
test submission with better than 1 arc second accuracy.
Also BDI Observatory can produce light curves and has
determined the rotational period of a number of
asteroids whose periods where previously unknown.
This led to the publication of a paper in the Minor
Planet Bulletin, (Caspari 2008). “Minor astronomical
discoveries from an inexpensive camera.”
Figure 10: SAC-8II as primary camera plus Quickcam
Pro 3000 attached to zoom lens operating as an
electronic finder scope
(http://www.peter-caspari.com/bdi)
While this configuration is not ideal for “pretty picture”
astrophotography it can still produce reasonable images
and false colour images using colour filters.
The telescope used at BDI Observatory is a basic home
built 8” f/6 Newtonian and the cameras used are the
SAC 8-II and Quickcam Pro 3000. The Quickcam Pro
3000 is used for occasional planetary imaging however
the SAC8-II is typically installed due to its sensitivity.
BDI observatory typically does asteroid related work.
The Quickcam pro is typically installed in a 35mm
zoom lens and operates as an electronic finder scope
capable of detecting stars down to magnitude 7. This is
an unmodified webcam however with the SC
modification this basic configuration could be used as a
guide scope with software freely available.
The total cost of this complete configuration would be
considerably less than a single high end purpose built
astro CCD camera such as those offered by SBIG
Figure 11: Spiral Galaxy M83 taken with the SAC8-II
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References
Caspari, P 2008: Minor Planet Bulletin, Edition 35-4,
185
DMweb: Webcams for Astroimaging,
http://homepage.ntlworld.com/molyned/webcameras.htm (2008)
DSSweb: Deep Sky Stacker,
http://deepskystacker.free.fr/ (Accessed 28 March
2009)
JCweb: Astrophotography,
http://www.geocities.com/jgroveuk/Astrophotography.
html (Accessed 26 March 2009)
Meadweb: Meade Telescopes, http://www.meade.com/
(Accessed 26 March 2009)
Figure 12: M42 close-up taken with the SAC8-II and
colour filters
MPCweb: Minor Planet Centre,
http://www.cfa.harvard.edu/iau/mpc.html (Accessed 28
March 2009)
Conclusion
Regiweb: Free image processing software,
http://www.astronomie.be/registax/ (2009)
Webcams and other digital cameras offer the amateur
astronomer a viable alternative to the significantly
more expensive purpose build astro CCD cameras.
Some of these options require some electronics skills to
implement however the cost savings can be dramatic.
SAweb: Paton Hawksley Education, Star Analyser,
http://www.patonhawksley.co.uk/staranalyser.html
(Accessed 26 March 2009)
SBIGweb: Santa Barbara Instrument Group,
http://www.sbig.com/ (2009)
The performance of these digital cameras can be
comparable to purpose built CCD cameras especially if
they are modified for long exposures.
SCweb: Poor Meadow Dyke Observatory,
http://www.pmdo.com/ (Accessed 26 March 2009)
Whether your interest is astrophotography, astrometry,
photometry or spectral analysis these cameras can offer
a real and inexpensive option. These cameras may
provide the all the functionality required or supplement
purpose built cameras. Either way their capabilities for
astro imaging can not be ignored.
SAOProjweb: HET 603 project, http://www.petercaspari.com/bdi/P100-HET603-PeterCaspari.pdf
(Accessed 26 March 2009)
VSweb: Visual Spec - home page,
http://www.astrosurf.com/vdesnoux/ (2008)
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