Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Flat Frames Over/Under Correcting Back to Back Subframes

  • Please log in to reply
6 replies to this topic

#1 SiriusFritz

SiriusFritz

    Lift Off

  • -----
  • topic starter
  • Posts: 3
  • Joined: 16 Feb 2020

Posted 05 June 2020 - 03:27 PM

Hello,

 

I've been having some serious issues with flats lately on my RC8. The two attached photos are calibrated subframes that were taken back to back with no focusing in between. 

 

You can see that one has decent correction and the other over corrects. Can this be caused by flexure in the system? I would think if I had that bad of flexure I would have a lot of other problems. 

 

When taking flats on my OrionED80 with the same camera/OAG I don't have this issue.

 

Thanks for any advice,

Fritz

Attached Thumbnails

  • over-correction.JPG
  • decent-correction.JPG


#2 SiriusFritz

SiriusFritz

    Lift Off

  • -----
  • topic starter
  • Posts: 3
  • Joined: 16 Feb 2020

Posted 05 June 2020 - 04:26 PM

Alright, something to add to this. If I do not subtract dark frames from the subframes I don't have this issue. Still not great flats, but the exposure to exposure issue is gone.



#3 jdupton

jdupton

    Mercury-Atlas

  • *****
  • Posts: 2,516
  • Joined: 21 Nov 2010
  • Loc: Central Texas, USA

Posted 05 June 2020 - 04:40 PM

Fritz,

 

   The only thing I can think of that might cause this is a change in cooling from frame to frame. If you are running at very high TEC power levels, the control may not be able to keep up. 

 

   Open the FITs Header process in PixInsight and see if your capture software recorded the actual sensor temperature from the camera in the frames. Compare the two you posted to see if there was a thermal change that might have caused a dark current change between exposures.

 

 

John

 

EDIT PS: You may need to go back to the original frames when you look at the FITs Headers. Some PI processes drop some FITs Keywords after operations are complete.


Edited by jdupton, 05 June 2020 - 04:43 PM.


#4 Peregrinatum

Peregrinatum

    Apollo

  • *****
  • Posts: 1,173
  • Joined: 27 Dec 2018
  • Loc: South Central Valley, Ca

Posted 05 June 2020 - 05:53 PM

What is your calibration process, and what type of camera do you have?


  • kingjamez and RossW like this

#5 SiriusFritz

SiriusFritz

    Lift Off

  • -----
  • topic starter
  • Posts: 3
  • Joined: 16 Feb 2020

Posted 05 June 2020 - 06:21 PM

What is your calibration process, and what type of camera do you have?

Thank you both for the replies. 
 

I checked the FITs header and they are both right at -15C. 
 

My camera is an Atik 383L mono.
 

When making my master flat I subtract bias only and no dark flats. The bias is taken at the same temperature as the flat, in this case -5C. When it comes to calibrating the final lights, I only use dark frames and the flat frame I just mentioned. I use Pixinsight for all processing.  

My flats are shot at 25k in SGP. 3.3 second exposure so safe from the shutter. 
 

Does having my flats at a different temperature than my lights possibly cause this?


Edited by SiriusFritz, 05 June 2020 - 06:26 PM.


#6 Peregrinatum

Peregrinatum

    Apollo

  • *****
  • Posts: 1,173
  • Joined: 27 Dec 2018
  • Loc: South Central Valley, Ca

Posted 05 June 2020 - 07:31 PM

Thank you both for the replies. 
 

I checked the FITs header and they are both right at -15C. 
 

My camera is an Atik 383L mono.
 

When making my master flat I subtract bias only and no dark flats. The bias is taken at the same temperature as the flat, in this case -5C. When it comes to calibrating the final lights, I only use dark frames and the flat frame I just mentioned. I use Pixinsight for all processing.  

My flats are shot at 25k in SGP. 3.3 second exposure so safe from the shutter. 
 

Does having my flats at a different temperature than my lights possibly cause this?

Just a little more info... what processes do you use in Pixinsight for calibration, and what settings.



#7 Peregrinatum

Peregrinatum

    Apollo

  • *****
  • Posts: 1,173
  • Joined: 27 Dec 2018
  • Loc: South Central Valley, Ca

Posted 06 June 2020 - 10:05 AM

watch these 3 adam block vids and it will answer all your questions:

 

https://www.youtube....kg441UBNpo&t=2s

 

https://www.youtube....h?v=SyLERe7ETJY

 

https://www.youtube....Vx07KIdDMU&t=3s




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics