I've decided to do my own collection of Messier object photos. Here is a photo of an object that I can barely see from my home latitude of 52.6ºN - M83, the Southern Pinwheel. It's 8.3 magnitude, but Declination 30ºS. Easily visible from latitudes such as Paris, Rome, New York, but venture back northward to the UK and it disappears into the murky brown skies we have here. It barely rises above the south horizon. When I took this photo it was about 6º up. (I also managed to get Ptolemy's cluster, M7 this night too!). Fortunately the observatory dome has a beautiful flat horizon, only spoilt by distant light pollution, which was exacerbated by moisture in the atmosphere after a hot, sunny day. During the long summer evening twilight, I managed to capture 10 flat field frames in a blank spot near Capella (at ~40% pixel saturation level) and thereafter I took 10 dark flat frames. So armed with a smooth flat I took 3x10", then a 20", followed by 16x30" exposures of M83, which individually looked like a yellowish blurry star on an intensely reddish brown background. I later got 4x30" dark frames. I spent the whole of the next day trying to stack them, but had to shrink each image by 50% so Deep Sky Stacker would pick up the stars, but once I did that, at 1 o'clock the following morning, the spiral arms finally revealed themselves! It definately needed the 16-bit image processing in DSS. After a quick cross-check using Starry Night Pro, I'd picked up PGC 48132, a 16.0 mag galaxy, which is just to the left, inside from 2 x 12 mag stars. What an achievement!
Tuesday 26 May 2009
An example of what a good 'flat' can do
I've decided to do my own collection of Messier object photos. Here is a photo of an object that I can barely see from my home latitude of 52.6ºN - M83, the Southern Pinwheel. It's 8.3 magnitude, but Declination 30ºS. Easily visible from latitudes such as Paris, Rome, New York, but venture back northward to the UK and it disappears into the murky brown skies we have here. It barely rises above the south horizon. When I took this photo it was about 6º up. (I also managed to get Ptolemy's cluster, M7 this night too!). Fortunately the observatory dome has a beautiful flat horizon, only spoilt by distant light pollution, which was exacerbated by moisture in the atmosphere after a hot, sunny day. During the long summer evening twilight, I managed to capture 10 flat field frames in a blank spot near Capella (at ~40% pixel saturation level) and thereafter I took 10 dark flat frames. So armed with a smooth flat I took 3x10", then a 20", followed by 16x30" exposures of M83, which individually looked like a yellowish blurry star on an intensely reddish brown background. I later got 4x30" dark frames. I spent the whole of the next day trying to stack them, but had to shrink each image by 50% so Deep Sky Stacker would pick up the stars, but once I did that, at 1 o'clock the following morning, the spiral arms finally revealed themselves! It definately needed the 16-bit image processing in DSS. After a quick cross-check using Starry Night Pro, I'd picked up PGC 48132, a 16.0 mag galaxy, which is just to the left, inside from 2 x 12 mag stars. What an achievement!
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