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A Weird Calibration Problem Solved

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#1 rwstanley

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Posted 03 February 2018 - 12:14 PM

I 'm posting this because I have run across some weird behavior that was causing calibration problems with my QHY 163M.  Since there are numerous threads on calibration problems with the ASI 1600mm which has the same chip, I was wondering if there might be some correlation.  The software I'm using is CCDAP,  Foocusmax V4, The SkyX CAO, and the ASCOM driver for the QHY 163M.  The problem occurs when I begin  an imaging run in CCDAP by focusing in Focusmax.  After the focus run there is an approximately 3500 ADU pedestal added to all  the subsequent images.  This isn't a terrible problem by itself, however if I close everything after the run and then  restart it at a later time to take calibration frames without using Focusmax  then the pedestal isn't added to the calibration frames and the calibration frames fail.  If I take the calibration frames immediately after the imaging run without shutting anything down then the pedestal is added and the calibration frames work fine.  This was driving me nuts until I figured it out.  Whether this has implications beyond my own particular setup I have no idea but I thought I would put it out there for someone who may be running into calibration problems to see if it might relate to what they are experiencing.

 

-Ron


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#2 rwstanley

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Posted 13 February 2018 - 02:30 PM

Just as a follow up on this.  It appears to me that it is a QHY driver problem.  The behavior described above only happens when a subframe is taken from a full frame.  The subframe and all of the frames taken after have an approximately 3200 ADU pedestal added to them.  The reason I associated it with Focusmax is because Focusmax takes a subframe when doing focusing but it really doesn't have anything to do with Focusmax at all.  It also happens in Maxim DL so it appears to be a QHY Ascom driver issue.  I have submitted this to the QHY Forum but have received no response.  I was wondering if anyone with a QHY 163M using the latest Ascom driver could check this to see if it is specific to my camera or if it is a common problem.

 

Thanks,

Ron



#3 GeneralT001

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Posted 13 February 2018 - 09:13 PM

Hi Ron,

 

Did you ever get your ASI1600 Pro back from ZWO? If yes, what did they find?

 

I got mine back and they adjusted some voltages for the pixels?

 

 

 

Tony



#4 rwstanley

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Posted 13 February 2018 - 10:39 PM

Hi Tony,

 

I sent my camera back to High Point Scientific and authorized by ZWO they sent me a new one, however even without the noise problem, I was having problems with the previous ones in the cold and where I live the camera is going to have to operate down to -20C. I sent the camera back to them. I never even opened the box and I had them send me a QHY 163M.  So far the QHY 163M has been pretty good after I figured out what was going on with the background counts. No pattern noise and it does calibrate well once you make sure all the backgrounds are the same and so far it has handled the cold well. 

 

Have you had a chance to use your camera?  Is it fixed?  I know the thread I started in December is still active on the ZWO forum so it seems that the problem is still cropping up.  Hopefully they have identified the problem and the new ones coming out are fixed.

 

-Ron



#5 GeneralT001

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Posted 14 February 2018 - 01:08 AM

Recently, I had to chance to try it out on M1 (Crab Nebula). Initially, I thought I still had an issue with the camera as there were a number of black pixels throughout the integrated image - but then I realized I had not done any dithering (it has been so long I forgot to activate it in SGP). I made a post about it and Sam saw the post and said I should send the camera back - AGAIN!

 

Needless to say, I wasn't thrilled at that prospect, so I had another opportunity to get some data on M1 again and this time I did remember to dither (I dithered each frame). Just to make sure that dithering wasn't the issue. Fortunately it appears that dithering was the issue as the new data looks relatively normal (I think):

 

M1_Ful_Pre_Process.JPG

 

So, for now, I am happy enough with the camera and just need more time to get more data. One thing this has taught me though, is I need another camera - just incase one breaks smile.gif.

 

 



#6 rwstanley

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Posted 14 February 2018 - 09:59 PM

Hi Tony,

 

Nice M1.  That certainly looks a lot better than before in terms of the pattern noise. Glad it's working out for you.

 

-Ron



#7 Jon Rista

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Posted 17 February 2018 - 10:24 AM

Ron, you said you figured out what was going on with the background counts. Does that mean you figured out why the pedestal was not being added? When you say pedestal, are you talking about the Offset setting in the driver, or something else?



#8 rwstanley

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Posted 17 February 2018 - 06:53 PM

Hi Jon,

 

When I connect to the camera and take an image, say a dark, it will have a background count of around 780.  If you then take a subframe of that dark, it will have a background count of around 4000 and all the images taken after that subframe will have a background count starting at around 4000.  If you don't take a subframe then all the images will have a background count starting at 780.  If you disconnect the camera and exit the control program, The SkyX or Maxim DL, and then restart the programs again and reconnect  to the camera, it will come back with a background count starting at 780 again.

 

This was driving me nuts because I would run a session and start it by using Focusmax which takes a full frame and then takes a subframe around the target star.  So all the images would have this 3200 ADU "pedestal" built in.  Then I would shut everything down and take calibration frames later.  The calibration frames wouldn't use a subframe so they would have a background starting at 780.  Naturally the calibration frames didn't work.  If I take a subframe before starting the calibration frames then everything comes out right. 

 

I am guessing that this is a problem with the QHY Ascom driver since everything else with the camera works fine but I don't really know since no one has given me feedback on whether their camera has exhibited this behavior.  I have posted this on the QHY Forum but no response so far.  I don't think it has anything to do with the true Offset setting since I have tried a couple of Gain and Offset settings and the behavior remains the same. 

 

-Ron 




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