Monday, March 11, 2013

ISO And Shutter Speed On Astrophotography

It was beautiful last night. I woke up about 1:30 a.m., drank some coffee, and then headed outside. These shots were made with an Orion 80mm refractor as a prime-focus lens for a Nikon D5100 DSLR. All of these photos are right out of the box--no sharpening, no noise reduction, no cropping. Clicking on these pics makes them bigger.
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Above is M13, the Great Globular Cluster in the constellation Hercules. 270 seconds with an ISO of 1000. I had a really tight alignment, so I dropped the ISO and lengthened the shutter speed.
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This is Vega, one of the Summer Triangle Stars. It's in the constellation Lyra. I typically find a bright star to tighten up my focus. Then I slew over to my object of interest. 335 seconds, ISO 800.
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This is M51, a spiral galaxy, also called The Whirlpool Nebula, in the constellation Canes Venatici, The Hunting Dogs. 255 seconds, ISO 800.
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M8, The Lagoon Nebula, in Sagittarius. 96 seconds, ISO 800.
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Another shot of M8. This time, 242 seconds, ISO 400.
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M17, The Horseshoe Nebula, also in Sagittarius. 194 seconds, ISO400.
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M20, The Trifid Nebula, again in Sagittarius. Kinda faint, huh? 123 seconds, ISO 400.
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M22, the second-best globular cluster viewable in the northern half of Earth. It's also in Sagittarius. 184 seconds, ISO 400.

You get better photos with longer exposures, but only if your alignment is rock-solid. Also, the lower ISO's need longer exposures, but there's much less "noise", those random colored pixels that aren't really there.

Posted by Dave.

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