Here's what you would get if you stack 6304 short exposures of the Orion Nebula taken with your unmodified DSLR in an extremely light polluted area and without an equatorial mount.
Noise has been added (dithering) to most images, including the wide-angle photo at the beginning of the video and the stacked image, to reduce color banding, blocking and flickering caused by youtube compression, particularly in the darker and fainter parts of the video. However, these artifacts are still quite noticeable at lower resolutions. Therefore, it is highly recommended to watch at maximum resolution for the best viewing experience. A 4K version of the video with less noise applied is available here: • Orion Nebula: Stacking...
Chapters
00:00 Introduction (zooming in, panning across)
02:28 Comparison
04:18 Creating the image
Taking a picture with your smartphone involves a specific amount of time for the camera sensor to gather the incoming light. In low-light conditions, such as at night, the exposure time must be extended to collect enough signal. This is the reason why your night photos are often not clear even if you get the right focus. Since the exposure time is longer, a slight shake during shooting will result in blurred images. The same applies to capturing faint deep sky objects; we need to gather as many signals as possible. One of the most important requirements to achieve this is to take long exposures. However, the Earth's rotation causes all the objects we see in the sky, including the moon and the sun, to appear in constant motion. So, there is a limit to the maximum exposure time we can use before everything gets blurred. For longer focal lengths, the exposure time needs to be shorter. The solution is to use an equatorial mount that aligns with the Earth's rotation, keeping the stars stationary for longer exposures. An alternative, though less effective, method is to take a large number of short exposures and stack them. Today I will be using this method to show one of the most popular targets for amateur astrophotographers, the Orion Nebula.
The video starts with a wide-angle view of the Orion constellation and zooms in on the Orion nebula, above which we can see the Running Man nebula. After panning across the stacked image, it then compares the stacked image with several other images. In the final section, I briefly show the steps I went through to produce this image.
Image details, sky conditions and camera specifications
Equipment-camera: Samsung NX3000 (unmodified)
Total number of frames (stacked image): 6304
Date of shooting: between 22 November 2020 and 12 April 2021 (Over 80% of the images were taken in February and March; 3118 in March, 2156 in February, 607 in April, 311 in December, 102 in January and 10 in November.)
Shooting hours: 20:20-03:44 UTC+3
Integration time (6304 subs): 4 hours 22 minutes 40 seconds
Total number of exposures taken before manual extraction of poor-quality frames (due to out of-focus- images, camera shake, corrupted files, low SNR at low altitudes above horizon, clouds, artificial objects, etc.): 9047 ± 400 frames
Location: Istanbul
Telescope: None
Mounts - tracking: None
Astronomical filters: No filters used - broadband imaging with a one-shot color camera
Calibration frames: 50 dark, 50 bias, 50 flat frames (adding them made hardly any difference)
Bortle dark sky scale: 9 (There is so much light pollution here that I was shocked the first time I was able to observe under a relatively darker sky; Venus was shining as if it were the moon. It also had a larger apparent diameter.)
Naked-eye limiting magnitude at zenith before astronomical dawn with v And being used as a reference star: about +4.5 (may vary from person to person)
Visual magnitude of the faintest stars that can be distinguished (in the stacked image): about 14,8 to 15,0
Exposure parameters of subs and shooting settings:
• Exposure time: 2,5 seconds
• F-number: f/5.6
• ISO speed: 3200
• Focal length: 200mm (50-200mm lens)
• Focus: Manual
• White balance: Automatic
• File format: RAW (16-bit)
• Shutter release: Wireless shutter control using Samsung smart camera app and direct contact using camera timer
Reference frame shooting time: 5 February 2021, 23:30 UTC+3
Hour angle of Orion Trapezium Cluster at the time the reference frame was taken (atmospheric effects disabled): 1h54,8m
Stacked image field size: 6°43,47’ by 4°29,72’ (6,7245° x 4,4954°)
Image scale per pixel: 4,4”/pixel
Temporary disk space required by DeepSkyStacker to calibrate and stack 6304 light frames: 768,3 GB
Disk space taken up by 6304 subs: 121,96 GB
Maximum character limit exceeded. For calculations and more details about the video, see the full description here: docs.google.com/document/d/1q...
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