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Example 3: Orion Nebulas, wide view
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 | A series of wider views of the nebulas in Orion were obtained by piggybacking a Canon EOS 20Da with a (80-200mm f/2.8) lens operating at 100mm f/4 on telescopes driven by a Paramount drive. The exposures ranged from 1 sec to 480 sec. An experiment was conducted to see if there was a distinction between a single 8-minute exposure and summing 8 one-minute exposures. The camera was set to ISO 800 with its long exposure "Noise Reduction" (NR) feature on. This mode takes an internal identical length exposure and subtracts it from the image, reducing exposure- and temperature-varying fixed pattern noise. This noise is well below the levels associated with the sky illumination however.
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| The images were registered with RegiStar, as previously described.
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 | Because the target was moving in the sky, it entered stronger levels of light pollution over the course of the exposures. Three sets were made:
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| A series of eight 1-minute exposures
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| A single 8-minute exposure
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| A second series of eight 1-minute exposures
If noise levels were dependent on the ambient light pollution, we would be able to make comparisons to assess the relative noise levels of the two exposure strategies
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7 x 1-min, scaled by 8/7
Standard deviation (red) = 10.66
mean (red) = 64.25
= 1.33 * 64.25^0.5
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1 x 8-min
9.15 = 1.09 * 70.50 ^ 0.5
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8 x 1-min
10.10 = 1.15 * 76.84 ^ 0.5
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| The sky brightness is increasing over the sequence of exposures, as can be seen by the increasing means. I don't think I can conclude very much from this. On the face of it, the single 8-minute exposure seems to have a tighter distribution (less noise) than the others, but the variation between the two multiple exposure stacks is higher than this difference, and without an obvious explanation.
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;){kind=small}
