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The Dumbbell Nebula, Messier 27, is a showpiece in small telescopes. it is quite bright and can be seen even in cities with moderate light pollution. The brightness enables reasonable images to be made with short exposure times. The image here shows what can be seen in a small telescope (about 6 inches) from a reasonably dark site, though the colors are more pastel teal.
M27 is younger than 15,000 years has a diameter of about 2 light years, and is expanding at a rate of 31 km/second.
Technical. This image was obtained with a Canon 7D Mark II 20-megapixel digital camera and 300 mm f/2.8 L IS II lens plus a 1.4x teleconverter giving 420 mm at f/4 and ISO 1600. No dark frame subtraction, no flat fields. Tracking with an Astrotrac and no guiding. A single 1 minute exposure with M27 low in the sky. I actually did many exposures, but after the first minute, a cable was getting caught causing subsequent images to be trailed. It is amazing what can be shown in such a short exposure. This image is shown at 2/3 full resolution.
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:
Modern DSLRs like the 7D 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 .
See my review of the Canon 7D Mark II and why it is so good for astrophotography: Canon 7D Mark II sensor analysis.
Keywords to this image = astrophoto-1 nebula Messier digital_astro canon_7d2
Image ID: m27.c08.13.2015_1min.0J6A5488.e-c1-1332s.jpg
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Last updated September 05, 2024