ORION NEBULA: double the frames to 2,000 at 1.5 sec exposure = greater detail

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RickBG
Posts: 56
Joined: Sat Feb 15, 2020 3:52 am

ORION NEBULA: double the frames to 2,000 at 1.5 sec exposure = greater detail

Post by RickBG »

Image
Orion Nebula taken on Feb. 2, 2021
This was my last chance to photo M42 and the maximum frames I can achieve before the upper balcony obscure its view. I live at a latitude of 25 degrees N which was a godsent when it came to last years planetary photography (43 deg). For now I will have to leave behind the Horsehead Nebula and the Pleiades for next year, and search for new and exciting targets. Looking over the three recent M42's, I like this the most because of its greater detail and tonal quality. All my deep sky images have been in 16 bits and the planets have been in 8 bits. I try to keep the noise low and the Trapezium visible. All M42's were acquisitioned from ver. 3.3 beta of SharpCap Pro and by using the "Brain" helped me determine the best parameters to use for obtaining the best results. Let me know what you think is your favorite M42 among the three I've taken and why.
timh
Posts: 159
Joined: Mon Aug 26, 2019 5:50 pm

Re: ORION NEBULA: double the frames to 2,000 at 1.5 sec exposure = greater detail

Post by timh »

Hi Rick,

I think that your second photo is best. The first was maybe oversmoothed in processing and the colours seem slightly too green in the third. I am never really sure though exactly what is 'right' in terms of colour and it does vary with minor tweaks in processing.

I guess that your sky background is very bright for BRAIN to have recommended subs as short as 1.5s but at least the Orion nebula is an object that is bright enough that it still works OK with short subs. While you are not capturing any of the extended nebulosity the short sub is good for getting dynamic range and contrast in the core - and indeed you are about resolving the Trapezium which would have been washed out in longer subs without the application of special post-processing (e.g. HDMR and range mask which are tools in PixInsight - maybe there are similar in Photoshop?).

One real advantage with live stacking in SC with such short subs is that you can let SC do the stacking work, feed in the right darks and lights, and just end up with a few autostacks to handle in post-processing. It will even take out the bad frames for you on the fly if you use the brightness and FWHM filters. This worked quite well for me when I was using a Dobsonian reflector which I operated in a similar way to the way that you have with lots of very short subs (3-5s).

My conclusions from using the Dob and short subs for astrophotography with a sensitive CMOS camera was that whil obviously not suitable for fainter objects and extended nebulae the ste up does in fact works surprisingly well for quite a range of objects - especially star clusters, globular clusters, the Orion nebula, the brighter galaxies (M31, M33, M106 etc) and that there is a lot there to enjoy.
Tim
RickBG
Posts: 56
Joined: Sat Feb 15, 2020 3:52 am

Re: ORION NEBULA: double the frames to 2,000 at 1.5 sec exposure = greater detail

Post by RickBG »

Image

Hi Tim,
Thanks for your comments. This is the same photo as one above but more detail is brought out through additional processing. I still feel it still needs further refinement which requires much more time in the learning process. That being said, with extremely short exposures (1.5 sec.), you can obtain much more data if you have a "fast setup". What I mean by a "fast setup" is incorporating a f/1.9 focal reducer (HyperStar) making the system 25 times shorter exposure than f/10. This setup does not require guiding nor an equatorial wedge and above all requires much less exposure time than conventional setups. This is the same setup that Stephen Hawkings used but his was a larger 11 inch SCT-Altaz telescope. Unfortunately this set up can only be used on SCT where the secondary mirror is replaced by the HyperStar. With very fast exposures you avoid noise issues in your images and cooling is not necessary since the gains you get are insignificant (if using CMOS low noise sensors). The very fast f/2 systems are used in the RASA by Celestron mainly for those only interested in deep sky astrophotography. Next year in November or early December would be a good time to take the recommended number of frames without the balcony being an issue using the same short exposure times.

Rick
timh
Posts: 159
Joined: Mon Aug 26, 2019 5:50 pm

Re: ORION NEBULA: double the frames to 2,000 at 1.5 sec exposure = greater detail

Post by timh »

Thanks Rick,

I have never used hyperstar - did have an SCT once but sold it. Yes that is extraordinarily fast and it is always interesting to see and compare results from the various set ups that folk have. That is one of the attractions of the gallery - and also a danger because it might make you buy something new :). I

I hope that you don't mind that I have taken the liberty of lining your picture up alongside one that I took earlier this winter on my Dobsonian set up because the principle of stacking short subs from a fast unguided telescope is in common.

My set up was a D = 250mm reflector (Skywatcher) at F 4.7 (Baader flattener), 8 s subframes, Astronomik UHC filter, gain 200 , total accumulation time 11 minutes using an ASI294 PRO camera. The low 11 minute total accumulation time was because Orion was low in the sky (51.4 deg N) and rapidly disappearing behind trees.

Your very fast set up plus (and longer time) has certainly gone amazingly deep and captured detail right across parts of the nebula barely even visible in mine. The focus and resolution don't look quite so sharp though and it still looks rather too green to me - although of course 'correct' colour is always debatable.

Tim
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RickBG
Posts: 56
Joined: Sat Feb 15, 2020 3:52 am

Re: ORION NEBULA: double the frames to 2,000 at 1.5 sec exposure = greater detail

Post by RickBG »

Image

Hi Tim,
Thanks for sharing your image of M42. I have made simple changes to the original image to get rid of most of the green. I agree it was bothering me too. Processing an image is not a science but an art. I have seen the many images of Orion Nebula, and it never ceases to amaze me the varied and psychedelic colors that are present on line. From what I have read, if the true colors where accurately represented, it would be boring to look at. As long we don't deviate toward the "extremes", and we feel the image is to our liking, that's what counts.

When processing my images, I will zoom in on parts of the image to determine if I'm going too far in my processing. This helps me to assess if any artifacts, noise or artificiality in the image will appear. I would recommend to zoom into your image and see if you notice excessive noise, artifacts and possible dark halos around the stars. When attempting to over sharpen or over process to bring out greater detail, noise issues and artifacts start to become more apparent. Sometimes there is a trade off or a balance between too much detail with too much noise or less detail with less noise. As you can see I have made several changes and I am sure it will not be my last. But with each change there is a sense of accomplishment and satisfaction. I believe we can all agree, "beauty is in the eyes of the beholder".

Rick
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