Unable to calibrate darks?

[tomb18]

Hi,
I have a series (20) of darks of 2 minutes in length.  If I open these in PixInsight and apply screen transfer, they look as expected.  There are column defects etc.
I then do an ImageCalibration with a superbias,  and take a look at the results, and they are completely transformed.  They no longer are anywhere near what they looked like when uncalibrated. All that appears is a perfectly black background with many "hot pixels" and no amount of stretching will show the column defects etc.
Now, I know my superbias is good because I have no issues at all with exposure of 20 and 30 minutes.  I have the same thing with 30 second, and 5 minute darks.
I have no idea what is going on.  Any suggestions?
Camera: STL11000M
Thanks, Tom

[bulrichl]

Did you capture Bias frames and dark frames at the same temperature?
What is the median of your superbias?
What is the median of your 2-min dark frames?

Generally, it is not a good idea to pre-calibrate the dark frames (or the integrated dark frames), albeit this is recommended in some widely used tutorials. See my guide, https://pixinsight.com/forum/index.php?topic=11968 .

Bernd

[tomb18]

Hi
The median of the superbias is 0.01254 and the 1 minute dark is 0.01334.
I'll study you guide.  Thanks, Tom

[bulrichl]

Hi Tom,

OK, thus no clipping is to be expected when calibrating the darks. Honestly, I don't understand your problem yet. The goal of image calibration is not to produce pretty master calibration frames, but to produce correctly calibrated light frames.

Please describe your issue in more detail. Which are the settings that you used for light frame calibration? What is the appearance of the calibrated light frames?

Bernd

[tomb18]

Well, I was preparing everything to provide some pictures for this thread, and today for some reason, everything is just perfect!  I have no idea why things weren't as they were yesterday.
All is fine.
Anyways, I processed my HDR frames using the 2 minute shots without the bias yesterday and judging from the result I can't complain.
For some reason, I can't upload this in the gallery or anywhere.  I press post, and the screen goes white and never returns.  The file is only 247kb in size.

So here is the result.  https://va2fsq.com/wp-content/uploads/M42-hubble-processed-32-resized.jpg
Thanks for the link after all this!