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Hi, I would really value the community's feedback on my first astrophotograph as an amateur. For over 30 years, I was a professional astronomer, having cut my teeth on CCD imaging and spectroscopy since the early 1980s. I was privileged enough to work at some of the best telescopes and sites in the world, including La Palma, La Silla, Hawaii and Siding Spring. I was lucky enough to be an early member in the Supernova Cosmology Project team, where extensive CCD imaging started us on the road to discovering the acceleration of the Universe. During my time as a professional astronomer, I always marvelled at the ability, knowledge and dedication of the "amateur" community. If ever there was a misnomer it is the word amateur applied to what you do. After moving away from research due to leadership commitments - I was Director of both the Anglo-Australian Telescope and Australia Telescope National Facility as well as Australia SKA Director - I have now retired to rural New Zealand, where one of the activities I would like to pursue is astrophotography. The photos on this site are the inspiration to me. I took this photo of the LMC last night and I would value any advice you could give me. This was taken on Canon 5D Mk II on Sky Adventurer mount with 105mm zoom lens at f/5.6 with 135 x 30 sec exposures. Reduced with PixInsight. Background correction and colour correction only applied post porcessing. Yes I know this was a big stack - but I didn't trust myself to get the Polar alignment right. A few things I noticed in the processing - average ellipticity 0.72. But FWHM = 2.5. I guess I focussed pretty well but the ellipticity is (presumably) dominated by the coma toward the field edge. I have a second-hand Canon 200mm f/2.8 prime lens on order for when the lockdown ends. The average shift between individual 30sec exposures was 0.3px, increasingly largely monotonically over 30-50 frames (15-20 minutes) when there would be a jump of 10px over a single frame. Is this normal behaviour for the Sky Adventurer? [Gear worm?] The jumps usually coincided with a lower SNR ratio, and were discarded from the final stack, as were a few taken in twilight - I found the SNR to be unacceptable until about 15mins before astronomical night. [As a professional this also usually marked the start of useable data for me]. Is 0.3px in 30sec an acceptable polar alignment with a 105mm focal length? Should I try to better? Or invest in auto guider? [Or better mount?] Finally on the picture itself. While I have a preference for natural colours - should I be looking to bring colours out more? Also is there more to bring out of the LMC's outer regions with an 75min exposure on an 105mm f/5.6 lens? It may be an aperture a few hundred thousand times less than the biggest telescopes I am imaged with but just as satisfying. Thank you for welcoming me into your community. Brian Boyle |
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Welcome, Brian! Greetings from Italy - almost at your anitipodes! I have 3 decades of experience ad an amateur astrophotograper, but I also have a University background in astrophysics, so I understand "both worlds" (well, I still have a lot to learn about both, but let me say "I speak both languages"). IN MY OPINION, there are two primary differences between the approach to astrophoto by pros and amateurs:
Now, regarding your image, this are some of my PERSONAL OPINIONS: 1) Very very good result. I would say extraordinary, as a first result! 2) The Sky adventurer is a wonderful toy, but it not designed for heavy equipment. The 5D+200 f/2.8 is too heavy, IMHO 3) When aligned properly the Sky Adventurer should be able to shoot well at 105mm for up to 1 minute (I use routinely 2' on 70 mm) 4) Image quality is what you can expect from optics not designed for astronomy. Even very expensive lenses are "not perfect", because they are not designed with fixed focus at infinity in mind (telescopes obviously are!). 5) IN MY HUMBLE OPINION you could remove better the gradients (use DBE instead of ABE) 6) Jump of 10 px on a single frame. Maybe a glitch in the mechanics, but I think is more probable an adjustment of the tripod due to soft terrain or temperature change that "clicks" the alluminum legs once extended. 7) Colors in astronomy... :-) Endless debate. There is no "real" color in astronomy since at night we use scotopic vision, so we are de facto totally blind to Ha and red in general. That's why HII regions appear blue (H-beta emission) in images taken with standard cameras, designed to mimic our spectral response. There is no rule, and any photographer develops his/her "touch". What I do is to use PixInsight's "photometric color calibration" and then saturate a bit. That's all. But also much more aggressive approaches are absolutely fine. To enhance H-alpha I sometimes use two tubes, but this is a long story (see for example https://www.astrobin.com/full/jojd08/0/) Welcome to Astrobin, and say hi to the southern sky for me! I've been down under only twice... :-( Luigi |
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Hi Brian, welcome to Astrobin! I'm an "Ex-tronomer", too. I worked in my PHD and postdoc times on cosmology with galaxy clusters in the framework of the PLANCK and EUCLID missions. After a few years of break from Astronomy I recently started, like you, astrophotography based on a star tracker. I think your picture is a very good start and I'm looking forward to see more in the future! Cheers, Jean-Claude |
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Brian Boyle: My thinking on the color in Astrophotos is that the color you see should be generally the correct color, but the saturation and contrast should be set to best differentiate real structures and please the eye. If "natural" color means what the eye would see, then usually the answer would be none at all! Unless your Canon 5D has had the IR block layer removed you will need to pump up the red/magenta range quite a bit to see the H2 regions with any clarity. You've done a great job with this first image. Pixinsight has an incredibly accurate and easy tool to set color balance - Photometric Color Calibration. With a DSLR image you will need to look up the approximate FOV center in RA and DEC but it will plate solve to refine. Then select a star type (I use G2V) and it will best fit the color balance to the correct star colors. Play with this kit a bit before you decide to buy much more. The mount is always the most important! So try to decide how serious you want to be about AP before you invest. Welcome to Astrobin and amateur astrophotography! |
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Thanks to everyone for their incredibly helpful advice and encouragement. Kevin: great feedback on the mount. It is quite a jump to go something like the HEQ5 or 6, but I suspect I will need to go there if my interest (and ability) continues to improve. I suspect it will be the HEQ6 to give myself the greatest number of options if I get into full scale reflectors. Can't beat aperture. Luigi: thanks for the advice on DBE. I agree that I could do a better job on the background. Will explore this in PixInsight. Your comment on the weight of the Canon 5D/200m combination is also helpful and is consistent with Kevin's advice on the mount. I have also been tempted by auto guiding, but I guess the mount in the foundation of good astrophotography. I have said "Ciao alle stelle del sud" for you. |
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| Luigi: I looked again at my data reduction, and realised that I had done a background neutralisation without applying the dynamic crop. After doing that I got a much better result, which I have now posted. Thanks so much for the valuable critique. |
