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Hickson Compact Groups (HCGs) are small, isolated system of four or more galaxies in close proximity to one another.  The magnitudes of the galaxies differ by less than 3.0.  Hickson identified 100 such compact groups.    

One is HGC 44 in Leo, sometimes known as the NGC 3190 Group. with members: NGC 3190; 3185; 3187; NGC 3193. 

This is data from DSW in new Mexico.  Takahashi FSQ 106; Paramount MyT; WSI 683 with Astrodon LRGB filters.

  • Lum: 16x900s
  • Red: 17x900s
  • Green: 14x900s
  • Blue: 16x900s

Total: 15 hours 45 minutes.

Processing in PI and PS.


02_NGC_3189_Small_Crop.thumb.jpg.893b0a856804b64f73fd893dfee11bc7.jpg

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Beautiful image - I need to try it one day!

There is a misty shine around the brighter objects - not unpleasant but it makes me wonder: do they get mist at DSW now and then?

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15 hours ago, gorann said:

Beautiful image - I need to try it one day!

There is a misty shine around the brighter objects - not unpleasant but it makes me wonder: do they get mist at DSW now and then?

No - they never get mist at DSW.  ...   :icon_biggrin:

However ....  some of the subs were poor quality, no doubt due to passing cloud.  I'm never sure at what point I should ditch a sub - is 'any signal' better than no signal?  If I cut out the poorer subs, I ended up with:

  • Lum: 8x900s
  • Red: 12x900s
  • Green: 10x900s
  • Blue: 16x900s

Total: 11 hours 30 minutes.

01_HCG_44_Small_Crop.thumb.jpg.85580c6db9b89cf05d8f65c4caecd156.jpg

Edited by gnomus
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I know the problem of when to throw out a sub and also wonder if poor data is better than no data. In this case I think throwing them out made a difference. The new version if clearly more crisp and very very nice!

I assume the only way to find out is trial and error. Maybe make two stacks, one with more or less all subs, and one with only the perfect ones, and then compare and maybe blend. It also has to do with the number of subs - a high number will dilute any small imperfections. I recently made a wide field with 1 min exposures so I got over 100 subs. When I went through them I throw out all the ones with satellites but later realized that it was probably a rather stupid thing to do since any trail would have been completely diluted by the other 99+ subs.

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16 hours ago, gorann said:

I know the problem of when to throw out a sub and also wonder if poor data is better than no data. In this case I think throwing them out made a difference. The new version if clearly more crisp and very very nice!

I assume the only way to find out is trial and error. Maybe make two stacks, one with more or less all subs, and one with only the perfect ones, and then compare and maybe blend. It also has to do with the number of subs - a high number will dilute any small imperfections. I recently made a wide field with 1 min exposures so I got over 100 subs. When I went through them I throw out all the ones with satellites but later realized that it was probably a rather stupid thing to do since any trail would have been completely diluted by the other 99+ subs.

Exactly.  But....  I find that when I make the two stacks, I cannot really tell much difference between them.  So I tend to keep the stack with more integration time.  The problems only seem to arise further down field once I begin stretching the data.  Of course, by then I have 'invested' a bit of time in the image and I am reluctant to go back.

Anyhow, I agree that in this case, rejecting the lesser quality stuff did seem to help.  Thanks again for your comment.

Edited by gnomus
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I like both versions Steve. It is hard to give an advice how to decide which sub should be sorted out. In gerneral I also take all subs I have, if they are not unsharp or too bright or showing misshaped stars. SNR is mostly better the more subs you have.

Jens

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Great image! The image with all the subs looks better IMO.  Sara wrote an article (Garbage in Garbage out--something like that) that is on point to this question.  I think her verdict was --throw them all into teh mix (within reason of course).  

Rodd

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