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Old 21-04-2021, 09:17 AM
Zuts
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M104, What went wrong

I recently spent 3 nights at Wiruna under dark skies. Amongst other things I shot M104. This is the last object from that weekend.

M104, The Sombrero Galaxy.

19 by 300 sec, Darks, Flats, Bias
ASI 2600 MC, No filters
Esprit 120 @F7

Bortle 2 sky

Processed in PixInsight

I am not happy with this image.

1. It is blown out, I thought 5 minute subs would be fine, should I try 3 minute subs on this object to reduce the glow?
2. Minimal resolution of the dust lanes. Am I being optimistic shooting this with a 120mm, F7, 840 mm FL refractor. Should I give up and crank up my Edge HD 9.25?
3. I had 2 runs of 12 subs each on this object. 5 were discarded as they were affected by poor guiding. The second run was done with the object low to the horizon. Should I never shoot low to the horizon?
3. Obviously need more subs.

Thanks for looking
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  #2  
Old 21-04-2021, 09:33 AM
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rustigsmed (Russell)
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hi zuts,

have you got a raw stack you can upload?
how does an individual sub look? i'd say it looks only a little bit over cooked, which a reprocess could perhaps sort out. but i'd still be fairly happy with this.

cheers

russ
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Old 21-04-2021, 10:13 AM
Zuts
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Quote:
Originally Posted by rustigsmed View Post
hi zuts,

have you got a raw stack you can upload?
how does an individual sub look? i'd say it looks only a little bit over cooked, which a reprocess could perhaps sort out. but i'd still be fairly happy with this.

cheers

russ
Hi Russ,

Here is a single cropped sub. No processing, but STF autostretch applied, plus it is calibrated and flat/bias/dark applied. The stack doesn't look that much different.
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Old 21-04-2021, 10:41 AM
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rustigsmed (Russell)
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Quote:
Originally Posted by Zuts View Post
Hi Russ,

Here is a single cropped sub. No processing, but STF autostretch applied, plus it is calibrated and flat/bias/dark applied. The stack doesn't look that much different.
I dont think it is overly blown out, but you may wish to alter your processing routine to keep the highlights down a tad. but i think its pretty good, not sure how low to the horizon you were shooting, would be a bit cleaner when it's higher up definitely.
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Old 21-04-2021, 11:13 AM
Startrek (Martin)
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Quote:
Originally Posted by Zuts View Post
I recently spent 3 nights at Wiruna under dark skies. Amongst other things I shot M104. This is the last object from that weekend.

M104, The Sombrero Galaxy.

19 by 300 sec, Darks, Flats, Bias
ASI 2600 MC, No filters
Esprit 120 @F7

Bortle 2 sky

Processed in PixInsight

I am not happy with this image.

1. It is blown out, I thought 5 minute subs would be fine, should I try 3 minute subs on this object to reduce the glow?
2. Minimal resolution of the dust lanes. Am I being optimistic shooting this with a 120mm, F7, 840 mm FL refractor. Should I give up and crank up my Edge HD 9.25?
3. I had 2 runs of 12 subs each on this object. 5 were discarded as they were affected by poor guiding. The second run was done with the object low to the horizon. Should I never shoot low to the horizon?
3. Obviously need more subs.

Thanks for looking

Atmospheric dispersion at low altitudes won’t blow your subs out , you usually end up with poor detail and fatter stars.
In any case try to image above 30degrees to minimise low level atmospheric dispersion
My best subs have always been up nice and high as you are not trying to punch through all that thick atmosphere with contains humidity (moisture) , air pollution , dust , you name it ( worse near Cities or built up areas )
My 2 cents ......
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Old 21-04-2021, 07:58 PM
JA
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Hi Zuts,

You don't say how hard you pushed the gain, or if you did at all, but that may be a factor as dynamic range will get compressed as gain rises and thereby increase the likelihood of any blowout, (Notwithstanding that the 2600MC has a sneaky/clever high res mode evident in the gain v Dynamic Range curve at gain >= 100)

Best
JA

Last edited by JA; 21-04-2021 at 08:09 PM.
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Old 21-04-2021, 09:43 PM
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cometcatcher (Kevin)
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Sometimes M104 needs processing like the Orion nebula. You may need shorter subs for the core, or processing so the core doesn't blow out. A midtone stretch for instance.

Other than what the others have said, it okay for a 120mm refractor. Your 9.25" SCT will reveal greater detail.
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Old 21-04-2021, 10:04 PM
Zuts
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Quote:
Originally Posted by rustigsmed View Post
I dont think it is overly blown out, but you may wish to alter your processing routine to keep the highlights down a tad. but i think its pretty good, not sure how low to the horizon you were shooting, would be a bit cleaner when it's higher up definitely.
Quote:
Originally Posted by Startrek View Post
Atmospheric dispersion at low altitudes won’t blow your subs out , you usually end up with poor detail and fatter stars.
In any case try to image above 30degrees to minimise low level atmospheric dispersion
My best subs have always been up nice and high as you are not trying to punch through all that thick atmosphere with contains humidity (moisture) , air pollution , dust , you name it ( worse near Cities or built up areas )
My 2 cents ......
Thanks Russell and Martin,

I am just learning PI, I agree it is rather blown out in my processing.

I should be more patient in my imaging and image in the top 2/3rds
of the sky but sometimes it's hard as I get few dark sky nights.

Quote:
Originally Posted by JA View Post
Hi Zuts,

You don't say how hard you pushed the gain, or if you did at all, but that may be a factor as dynamic range will get compressed as gain rises and thereby increase the likelihood of any blowout, (Notwithstanding that the 2600MC has a sneaky/clever high res mode evident in the gain v Dynamic Range curve at gain >= 100)

Best
JA
Thanks JA,

Yes, I image at Gain 100 to try and take advantage of that mode.

Quote:
Originally Posted by cometcatcher View Post
Sometimes M104 needs processing like the Orion nebula. You may need shorter subs for the core, or processing so the core doesn't blow out. A midtone stretch for instance.

Other than what the others have said, it okay for a 120mm refractor. Your 9.25" SCT will reveal greater detail.
Thanks Kevin,

I think you are correct, I need to crank up the 9.25. Even with better processing and more subs, I don't think I will get much more detail.
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