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Is there IFN around M101?

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#1 diggy

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Posted 25 May 2020 - 06:39 PM

I know that M101 is a difficult target, esp. to capture the dim spirals.  But this year I noticed a lot of what I first took as noise in the background.  I've attached a purposely-over-stretched (and noisy) version to show the pattern.  But when I compared it to a version I took a year or so ago, with very different equipment, the same backgound pattern shows up.   So my question is, is there any significant IFN around the galaxy (as there is, for example, around M81-82?)M101_3.jpg


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#2 bobFranke

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Posted 26 May 2020 - 12:50 AM

m101Inv.jpg

If there is IFN, it is extremely faint. At f/5 with 40 15-minute luminance sub exposures, I cannot see it.

 

Your image appears to have large dust donuts. Relative to the galaxy, they are at 2 and 4 o'clock. It is plainly visible that these two artifacts are circular. The one at 2 o'clock appears larger and goes off the frame.

 

Hope this helps.

 

Cheers,
Bob
http://bf-astro.com/



#3 ManuelJ

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Posted 26 May 2020 - 03:12 AM

Yes, there is very faint IFN, but what you see in your image is incorrect flats calibration.



#4 DrGomer

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Posted 26 May 2020 - 09:44 AM

The checker pattern, which I recently understood with my new 183mm, is showing up too from lacking or improper flat calibration. 



#5 Jared

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Posted 26 May 2020 - 01:16 PM

Yes, it's there, but it's very, very faint. What you are seeing in your image, though, is a couple of dust donuts and (most likely) a slight focus difference between your flats and your lights, thus slightly altering the vignetting amounts across the frame.  Getting perfect flats can be hard.  If you are going to stretch down to the limits of atmospheric extinction, these problems commonly appear. 


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#6 diggy

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Posted 26 May 2020 - 01:59 PM

Yes, it's there, but it's very, very faint. What you are seeing in your image, though, is a couple of dust donuts and (most likely) a slight focus difference between your flats and your lights, thus slightly altering the vignetting amounts across the frame.  Getting perfect flats can be hard.  If you are going to stretch down to the limits of atmospheric extinction, these problems commonly appear. 

Hmmm...the flats idea never occurred to me.  I didn't think flats had to be focused, since I'm looking at a blank field (flat panel, t-shirt, clear sky, etc).  I typically use sky flats these days.  Given the ASI183MM-pro, I don't do flat darks; instead I calibrate the flats with bias master of appropriate gain and temp.  I generally have no problem with these flats.  I'll take another look.




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