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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. 1 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). 2 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) 3 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) 4 (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 5 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) 6