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Artifacts  

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(@centaurus)
Brown Dwarf Customer
Joined: 3 years ago
Posts: 6
December 9, 2019 21:55  

Please help! The integration frame shows artifacts, like shadows of the brighter stars of  M 45. The shadows don't show on the individual frames, I checked and rechecked them. I used the default settings of APP, light frames, master flat, dark and bias. MDark and MBias have been used in the past for processing with the same ISO/exposure time without any problem. To nail it down I noticed the first appearance of the shadows after normalisation, and clear shadows after integration. I have no idea what goes wrong. Can anyone help me please?  


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3694
December 10, 2019 13:49  

Could you maybe pinpoint as to what you mean with the shadows? I can't see anything really strange, apart from the gradient in the image.


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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1112
December 10, 2019 15:48  

When you click on the image you'll see reflections of the bright stars just above and slightly to the right of the stars.


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(@centaurus)
Brown Dwarf Customer
Joined: 3 years ago
Posts: 6
December 11, 2019 09:29  

Thank you, wvreeven, reflections are the right word, and for helping to point at the positions.


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3694
December 11, 2019 15:46  

Ah right, I was looking for darker artefacts. 😉 Thanks Wouter. So are you sure they are not visible in your single frames? They will show up very faintly probably and when stacked pop out more. It seems extremely likely these are actual reflections in the data, stars look like they have been registered properly and they show up for the brightest of stars, which makes sense as well.


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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1112
December 11, 2019 17:02  

I agree with Vincent. Probably stretching the original light subs VERY much will make them visible there as well. It looks like reflections in the optical train to me.

 

Wouter


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(@centaurus)
Brown Dwarf Customer
Joined: 3 years ago
Posts: 6
December 11, 2019 17:34  

Thank you for dealing with my issue. I went through all my subs again and didn't find anything strange in the original data. I took subs of a different target with the same configuration the same night, and the integration went well as usual. I have no idea what haunts me with M 45. I'd probably better discard the subs and try again.


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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1112
December 11, 2019 17:37  

Do the subs of the other target also contain magnitude 5 and brighter stars? Could you perhaps share one of the raw M 45 subs with us?

 

Wouter


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3694
December 11, 2019 17:46  

Yes it would be great if you could upload a single frame for us to have a look at. Nothing really haunts you I'm sure, the stars in this target are extremely bright so that would make sense.


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(@centaurus)
Brown Dwarf Customer
Joined: 3 years ago
Posts: 6
December 12, 2019 07:37  

Wvreeven, the subs of the other target don't contain such bright stars. The M45 sub is larger than 30 MB - would resizing affect the 'screening' ? Sorry I'm a newbie - is there any way of preprocessing with APP or taking subs  I could 'tame' bright stars against faint nebulosities? The same problem appears e.g.with Flame and Horsehead nebulae and Alnitak.


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(@wvreeven)
Quasar Admin
Joined: 3 years ago
Posts: 1112
December 12, 2019 09:52  

Perhaps you could use a system like WeTransfer to make a sub available?


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(@centaurus)
Brown Dwarf Customer
Joined: 3 years ago
Posts: 6
December 12, 2019 21:32  
SM 45 LIGHT 20s 800iso 20191205 19h23m51s322ms

I attached the cropped but otherwise unchanged file that contains the bright stars that trouble me. I hope this works.


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(@vincent-mod)
Universe Admin
Joined: 4 years ago
Posts: 3694
December 12, 2019 22:25  

Thank you! So I marked the position of the reflection in this light, it's faint, but it is there. So the problem is that you have a reflection going on in the image-train.

Screenshot 2019 12 12 at 21.23.28

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(@centaurus)
Brown Dwarf Customer
Joined: 3 years ago
Posts: 6
December 13, 2019 18:41  

I can see the reflection on your stretched image  but not on my own ones. I think it's best deleting my M 45 subs and try again another night. Thank you Vincent!


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