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The Constellation Cygnus, the Swan, contains many deep-sky object visible to Northern Hemisphere observers in the summertime. Prominent in this image below center, right is the star Gamma Cygnus, Sadr, and the blue stars near the upper left edge the brightest star in the constellation, Alpha Cygnus, Deneb. The pinkish-red colors in this region are hydrogen emission nebulae. The hydrogen emission in this region is redder than normal because interstellar dust, which is reddish-brown in the image, preferentially absorbs the blue H-beta and H-gamma emissions from hydrogen The plane of the Milky Way galaxy runs from lower right to upper left.
The Sigma 105mm f/1.4 DG HSM Art Lens on a Canon EOS 6D Mark II DSLR Camera provided this stunning image. The camera is stock, and the fact that it picket up so much hydrogen emission shows that it is very sensitive.
Technical. This image was obtained with a Canon EOS 6D Mark II DSLR Camera and Sigma 105mm f/1.4 DG HSM Art Lens at f/1.4 and ISO 1600. No dark frame subtraction, no flat fields. Tracking with a Fornax Lightrack II and no guiding. This is a portion of the top frame of a 3-frame mosaic. The image is a stack of 28 images, with each exposure 30 seconds. No noise is apparent in the image--those are all stars. The total exposure was 14 minutes. The full resolution image plate scale is 11.2 arc-seconds per pixel. The image presented here is at 2/3 full scale, 16.8 arc-seconds per pixel.
Post processing: Raw conversion with Rawtherapee with settings tuned for astrophotos, including maintaining star color in saturated stars. Output color space was Rec.2020 to match the future of high dynamic range TVs. Look for a future article on this topic. Stretched with rnc-color-stretch. Also see Astrophotography Image Processing Basic Work Flow.
This is a natural color image. The high dynamic range of astrophotos must be stretched to bring out the range of details the camera recorded. But the typical image stretch process loses color for brighter subjects (e.g. stars and the brighter parts of deep sky objects become whiter as they are made brighter). This image uses a new algorithm that does not lose color during the stretch. The new algorithm enables fainter details to be shown and with less noise. Learn about the new software and download it free (open source) here: rnc-color-stretch.
The Exposure Factors, CEF, CEFA are measures of the relative amounts of light received from a subject. It can be used to fairly compare wildly different lens/telescope apertures and exposure times. For this image:
Larger image, 1220 x 1888 pixels, 1.3 megabytes.
Modern DSLRs like the 6D Mark II include on sensor dark current suppression and low fixed pattern noise at ISOs around 1600 and higher, making no need for dark frame subtraction. Modern raw converters correct for light fall-off and also correct for hot/dead/stuck pixels. This makes processing low light images easy: simply align and average.
To learn how to obtain stunning images like this, please visit my Extensive Articles on Photography .
Keywords to this image = astrophoto-1 galaxy Messier nebula star_cluster night low-light digital_astro mosaic canon_6D2
Image ID: cygnus-105mm-6d2-rnclark-img4840-4929-c08-11-2018-f-c2-.66x-2000vs.jpg
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Last updated September 05, 2024