NGC 7331

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oopfan
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NGC 7331

Post by oopfan » Tue Aug 01, 2017 8:46 pm

Here is my first attempt at imaging a galaxy. It is not perfect. My biggest mistake was reusing darks from the previous night when the ambient temperature was a couple degrees Fahrenheit cooler. I will never make that mistake again. I did not even check to see how different the sensor temperature was. Going forward I am going to keep a watchful eye on sensor temperature, and redo darks if it changes.

I know that I need more integration time but there are different ways of achieving that: (1) increase the exposure time and keep the number of subframes the same, or (2) increase the number of subframes but keep the exposure time the same, or (3) some combination of increased exposure time and increased number of subframes.

My first guess was to increase the exposure time. Unfortunately with an uncooled camera I think that I have already reached the point of diminishing returns. So my gut now tells me to keep the same 2 min exposure time but double the number of subframes.

Does that sound like a reasonable course of action? Thank you!

My image of NGC 7331 at AstroBin

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admin
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Re: NGC 7331

Post by admin » Wed Aug 02, 2017 2:55 pm

Good image!

I would recommend using more exposures and keeping the length of the subs down to the 30s-120s range. The theory of very long exposures for deep sky imaging as purely a response to the very high read noise of CCD cameras - since modern CMOS cameras have much lower read noise it's possible to obtain good results by stacking a larger number of shorter frames.

cheers,

Robin

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oopfan
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Re: NGC 7331

Post by oopfan » Wed Aug 02, 2017 3:02 pm

Thank you, Robin. I totally agree.

With my image of NGC 7331 I have already proven that a 2 minute exposure is long enough to capture the faintest wisps of nebulosity -- so going longer isn't going to win me anything -- it is actually going to make things worse.

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Re: NGC 7331

Post by oopfan » Wed Aug 02, 2017 3:22 pm

Hmm, yes, I think I might back down to 90 sec subs. I looked back at my camera settings file for the darks and compared it to the lights. The darks were captured at 12.5C and the lights at 13.2C. To me with my limited experience that is not a huge difference. So I think that 120 sec subs are out, and 90 sec subs are in. I just hope that 90 sec subs can capture the faintest wisps of nebulosity in NGC 7331.

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