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Why won't bias frames calibrate?

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#1 sdeming

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Posted 19 January 2021 - 02:05 PM

I realize I'm abusing this forum, since this is my third post just today, but I am new at this and being here has helped tremendously in fixing issues and learning new and better ways of doing things. I'm eternally grateful to all who have helped!

 

So, here's my question - Why won't my bias frames calibrate in Deep Sky Stacker? I've tried everything. I know my bias frames and master are correct. I even created new frames over the weekend. I covered the camera, set the temp to -15 which is where I am always shooting (and I know setting the temp isn't necessary) and I set the gain at the same gain as my lights. Then, I shoot at the fastest possible exposure. When I bring them into DSS it ALWAYS creates a posterized image, like the one below. I want to add bias frames, but have been unable to do so. Any suggestions or ideas would be greatly appreciated.

 

Thank you!

 

Scott

 

 

Attached Thumbnails

  • CT stacked with bias jpeg resized.jpg


#2 David Boulanger

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Posted 19 January 2021 - 02:23 PM

What camera?  I think I have read that some cameras require a slightly longer exposure.  Not 100% sure on that though.



#3 sdeming

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Posted 19 January 2021 - 02:43 PM

What camera?  I think I have read that some cameras require a slightly longer exposure.  Not 100% sure on that though.

QHY294C



#4 colinrm

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Posted 19 January 2021 - 03:08 PM

I had a similar issue before with my ZWO camera.  May not be relevant to you and your camera at all, but in my case, the white balance settings in the ASCOM driver for the camera were different between the lights and the biases.  This caused the bias to over correct the lights when applied, giving a similar experience for me to what you showed.  Might be something to consider and look into.



#5 sdeming

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Posted 19 January 2021 - 03:19 PM

I had a similar issue before with my ZWO camera.  May not be relevant to you and your camera at all, but in my case, the white balance settings in the ASCOM driver for the camera were different between the lights and the biases.  This caused the bias to over correct the lights when applied, giving a similar experience for me to what you showed.  Might be something to consider and look into.

How did you know the correct white balance for the bias?



#6 jessebear

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Posted 19 January 2021 - 03:19 PM

Same thing was happening for me with a Canon 550D. Bias frames ruined everything I added them to, and I'm pretty sure I did them correctly. In the end I just processed with lights, darks, flats, and dark flats. I haven't had a chance to try again lately.
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#7 bignerdguy

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Posted 19 January 2021 - 08:34 PM

First off i hope that the image you used as an example wasn't a bias frame.  if so that might be your issue.  Bias frames are the same as a dark frame but at a minimum time setting.  You usually cover the telescope and take a picture of nothing.  This lets the camera capture the imager noise. The example shot you used look like a light frame.  if that is an example of an actual bias frame there is something seriously wrong with that camera!

 

Also the exposure is the quickest time setting you can get from your camera and if there is an ISO setting you need to set it to match the light frames. Temperature also needs to be the exact same or DSS wont use it to calibrate any frame that doesn't match that temp.  Best way to use them anyway is if you can modify the header, assuming you use FITS files.  If you modify the FITS header and remove the CCD Temp setting it will apply it anyway.  However it will need to be optimized to do so or it may be inaccurate.



#8 sdeming

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Posted 19 January 2021 - 09:19 PM

First off i hope that the image you used as an example wasn't a bias frame.  if so that might be your issue.  Bias frames are the same as a dark frame but at a minimum time setting.  You usually cover the telescope and take a picture of nothing.  This lets the camera capture the imager noise. The example shot you used look like a light frame.  if that is an example of an actual bias frame there is something seriously wrong with that camera!

 

Also the exposure is the quickest time setting you can get from your camera and if there is an ISO setting you need to set it to match the light frames. Temperature also needs to be the exact same or DSS wont use it to calibrate any frame that doesn't match that temp.  Best way to use them anyway is if you can modify the header, assuming you use FITS files.  If you modify the FITS header and remove the CCD Temp setting it will apply it anyway.  However it will need to be optimized to do so or it may be inaccurate.

That image is a stacked image with bias frames applied. When I stack without bias frames I have no issues. As I wrote in my post, I matched temp and gain and used the fastest exposure setting. I’ve done this so many times and have never been able to get it to work.



#9 Borodog

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Posted 19 January 2021 - 09:33 PM

Have you tried dark flats instead? 



#10 sdeming

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Posted 19 January 2021 - 09:36 PM

Have you tried dark flats instead? 

Yes, I’ve always used dark flats and they have worked quite well. I’m just trying to cover all bases but pretty much ready to give up on bias frames. 


Edited by sdeming, 19 January 2021 - 09:36 PM.



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