The Great Orion Nebula & The Trapezium
Object Data: The Great Orion Nebula (M42, NGC 1976) is located in the 'Sword' part of the constellation of Orion, just below Alnitak, the Eastern-most of the three stars that comprise Orion's belt. As well as being the brightest, M42 is perhaps the most famous and most photographed nebula in the night sky. With a visual magnitude of 4.0 it has undoubtedly been observed since antiquity but its nebulous nature was probably not recognised until telescopes were first turned on it. The famous comet hunter Charles Messier first catalogued it in October 1764. Approximately 1,270 light years distant, M42 is a very active and turbulent cloud of gas and dust and an important star forming region of particular interest to astronomers. There are many hot young stars (most notably the 4 Trapezium stars close together in the centre) which fuel the dense swathes of surrounding gas, causing it to ionize and produce a red emission glow. M42 has a particularly complex range of of emission sources as part of it's spectrum, as well as a strong component of reflected broadband light, which probably accounts for the wide range of visible colours.
Photo for Reference to my images further below.
Image credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team.
Click for original page at NASA/ESA.
Location: Grantham, Lincs, UK
Conditions: Calm, very cold (near freezing), transparency=7, seeing=8
Optics: Orion Skyquest XT10i OTA f/4.7 10" Primary Reflector telescope
Mount: Standard "push-to" Dobsonian Mount - no EQ tracking!
Camera: Un-modified Philips SPC900NC Webcam + IR Filter at prime focus
Guiding: No guiding!
Exposure: 640x480 AVI @ 5fps 50 secs reduced to 30 secs for useful image frame size. K3CCDTools 2x Mode.
Processing: Image acquisition and initial processing using K3CCDTools, post-processing in Photoshop.
The night I took the photographs below I had originally intended just to take some shots of The Pleiades to try out my new Focal Reducer, and had set the webcam to monochrome mode. I couldn't get focused with the webcam using the FR, so a little disgruntled I removed it and thought I would try the Orion Nebula instead, and this proved surprisingly successful given the method I use.
In hindsight I wish I had attempted taking colour shots. The false colour versions below were created by some Photoshop trickery, so even though I enjoyed turning the black & white versions of the images into colour, they are not truly representative, although I did make reference to professional photos of M42 (I am however mildly colourblind!), and my humble little webcam was not able to gather as much light as a Hubble telescope (as in the above photo)!!!
First have a look at the movie footage captured directly through the Orion Skyquest XT10i telescope, as it gives you a good sense of what I actually saw, although to the naked eye the nebulosity appears brighter than in the movie, but monochrome of course. (Note that this movie was shot at 640x480, but is shown here compressed to half size at 320x240).
Click for M42 movie footage - (requires Quicktime or similar viewer).
Click for second M42 movie footage
K3CCDTools was used to capture the movie and perform the post-processing to align the frames, stack them and enhance to give this single still shot. During the post-processing, which was very late at night after bringing the laptop back indoors, I forgot to reset the display back to normal brightness, so the display was giving me a much darker image. This meant that I over-compensated on the Histogram, Gamma and Unsharp Mask and this resulted in a very grainy looking image, in the true light of day.
Fig. 1 - M42 Great Orion Nebula showing The Trapezium at centre (1st attempt overcooked!)
I still marvel at how much extra detail is actually contained in the data of the initial AVI footage, and just what can be achieved by the software.
Ok, so the Orion Nebula is the brightest nebula in the Northern Hemisphere making it a good candidate for my method of astrophotography, but consider the following points:-
- A cheap webcam was used on...
- a dobsonian mounted telescope...
- taking just 30 seconds of movie footage...
- with no equatorial tracking (the scope remains static)!
I think it's quite a good achievement. Doing it this way certainly makes you appreciate (long for) an EQ mounted telescope, but you also learn a lot about refining your technique, and making the most of what you've got.
The fun is in the challenge of it. It's definitely not easy! Let's just say I'm quite patient and determined.
The hardest part is getting the telescope sighted up on the target and focusing the webcam initially. With a dob, moved by-hand, making fine diagonal adjustments is not practical, you generally adjust the Altitude first, then rotate the dob base in Azimuth to a point where the target object is just about to come into view on the edge of the webcam preview screen on the laptop, then you leave the scope still while the target marches across the screen and disappears off the other side. This happens in about 40 seconds, in which you must work quickly to adjust Gain on the webcam, and focus the telescope. Usually this takes several attempts, lining up and focusing. So you have to repeat the steps over again. You need a steady hand, a well-balanced scope, with the dobsonian Alt and Az bearings working as smoothly as possible.
Without EQ tracking time is of the essence - the target is constantly moving out of the field of view, so every 30-40 seconds or so you have to repeatedly re-position the scope, adjust the webcam settings again and finely adjust the focus for the stars. Once focused you have to refine the webcam settings for Gain, Contrast, Brightness, Gamma, Frames per Second, which may take another 10 or 20 alignments of the scope.
So far you've probably spent the best part of an hour just getting set up. Finally you can actually take the capture, preferably several so you've got some choices on which is best. And then of course you need to process the footage back indoors, which might take another half-hour or more tweaking the image. All for a suitable single 30-second clip that can be processed into the single image as shown below.
Click here for more Technical Setup details and Tips on How to use the Philips SPC900NC Webcam for Astrophotography.
Eventually I had two good AVI's which resulted in the shots, one above and second directly below. I had rotated the webcam in the focuser at some point, in an attempt to make aligning the scope with the moving target easier, which is why one photo is at 90° to the other.
Fig.2 - M42 and Trapezium (at 90 degrees to previous shot, 1st attempt overcooked!)
A couple of days later I had a second go with the same footage to re-process the images in K3CCDTools to try and get better sized, and more accurate representations of the image. This time I used K3CCDTools "2x Mode" to prepare and save pictures double the size of the initial attempts.
Fig. 3 - Finer, more objective processing and larger (click to view full size).
Fig. 4 - Similar re-processed image, taking more care to finely adjust for realism.
Fig. 5 - False colour, rotated version of Fig 4 to be nearer actual orientation. Photoshop was used to apply Colour Balance on different layered copies of the image, with Curves, Levels, Brightness and Contrast adjustment layers used to enhance different aspects of the picture.
Fig. 6 - Similar Fig 4 re-processed, Photoshop false colour applied, plus gaussian blurring to soften the nebulosity.
There is without a doubt a high degree of "artistic license" in the post-processing I have applied, but the thought remains that the photon patterns entering your eyes from these images originated indirectly, from the Great Orion Nebula about 1,270 years ago, arrived here at Earth through my telescope, then onto the Internet, into your house, your computer and finally your eyes! That's an incredible 8.81793806e+15 miles away.
And when compared to the Hubble photo at the top of the page, I'm quite pleased, and I hope this encourages other amateurs to give it a go.
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- K3CCDTools - This software allows you to take better control over your webcam to capture movie footage or still shots to your computer for later enhancement by K3CCDTools, or another software such as Registax. It is reasonably priced and has many advanced features that give special control over exposure and gain that your standard Webcam software may not provide. K3CCDTools is particularly of interest because it includes settings that hook into a "long exposure modified" webcam (Note that long exposures are useless without proper equatorial tracking).