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Ha Mystery

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#1 griwei

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Posted 13 August 2020 - 12:14 PM

I doubt this will remain a mystery, given the collective knowledge of this group.

 

I've attached a couple of screen shots, one a 300 minute sub and the other a 420 minute sub.  Both were taken last night at Highland Glen Conservation Area on the southern shore of Lake Huron (Bortle 3) at around 3AM.

 

The exact same equipment was used: Redcat51 with ASI183MM Pro and Zwo filter wheel, using Optolong 7nm Ha filter.  Subs of the exact same length were also taken using Optolong's Pro filter.  They show much less pronounced flare, suggesting that the flare light source was mostly around the red side of the spectrum.

 

The rig was located about 2 meters from another one with an Orion ED80T CF on it.  I was using a red head lamp (generally pointed directly downward as I moved about). The nearest city was Sarnia - Port Huron, about 30km's to the west.  Needless to say, the scope was pretty much pointing straight up though, and the area was surrounded by very tall trees, about 25 meters away on the west side.

 

Oh, and it is possible (although I am not with the equipment to check at this time) that there might also have been an additional filter screwed into the RedCat's filter chamber (with possible candidates being IR-Cut or UHC).

 

So, what do you think I did wrong here?

 

Thanks.

 

 

Attached Thumbnails

  • Screen Shot 2020-08-13 at 12.38.34 PM.jpg
  • Screen Shot 2020-08-13 at 12.55.22 PM.jpg


#2 P_Myers

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Posted 13 August 2020 - 12:18 PM


300 min. & 480 min at 3AM????

didn't realize it would stay dark for that long? smile.gif
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#3 sg6

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Posted 13 August 2020 - 12:18 PM

You mean the ampglow?

Do you mean 300 miuntes and 420 minute sub ? That is a single 5 hour and a single 7 hour exposure.


Edited by sg6, 13 August 2020 - 12:33 PM.


#4 Becomart

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Posted 13 August 2020 - 12:23 PM

This I believe is amp glow and can be calibrated out.



#5 Hawkdl2

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Posted 13 August 2020 - 12:30 PM

All you are seeing is glow from the camera sensor's electronics - commonly but incorrectly called "Amp glow".   In any case, it is expected from your camera and can usually be calibrated out with a proper dark master - preferably taken at the same exposure - not a challenge if you meant seconds rather than minutes.    

 

Here's a link to ZWO's site that presents examples of the glow expected from the various sensors used in their cameras and approaches to minimize or remove the glow.

 

https://astronomy-im...s-amp-glow.html

 

Nice images, BTW.  


Edited by Hawkdl2, 13 August 2020 - 12:30 PM.


#6 terry59

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Posted 13 August 2020 - 12:38 PM

It is amp glow and is removed with darks. The gain must be the same for both. I add a pedestal to my darks



#7 OldManSky

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Posted 13 August 2020 - 05:44 PM

I'm pretty sure you meant 300 *seconds* and 420 *seconds.*

And yes, that's normal 183 amp glow.

Take darks of the same temperature, gain, offset, and length.

It'll disappear.

 

My normal Ha lights are 360 seconds.  The amp glow calibrates out just fine. First file -- raw sub, no calibration.

Second file:  calibrated light (darks & flats).

 

 

Attached Thumbnails

  • asi183_singlesub.jpg
  • asi183_stacknoglow.jpg


#8 17.5Dob

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Posted 13 August 2020 - 07:32 PM

I assume you are talking about the very distinctive amp glow pattern of the 183....it's famous for that..



#9 griwei

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Posted 14 August 2020 - 02:58 PM

You mean the ampglow?

Do you mean 300 miuntes and 420 minute sub ? That is a single 5 hour and a single 7 hour exposure.

Whoops. 

 

Minutes ... seconds...

 

Time really does fly when one passes 50, I guess!



#10 griwei

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Posted 14 August 2020 - 03:02 PM

You mean the ampglow?

Do you mean 300 miuntes and 420 minute sub ? That is a single 5 hour and a single 7 hour exposure.

So that's amp glow!!!

 

I only recently started going past 180 seconds, having gained the confidence to stretch things out.  Hence, I had only heard of, but never encountered it.

 

Thanks very much for the explanation.




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