Hypercam 183C can not calibrate out sensor glow

[tristarcapt]

Hello, I have an Altair Hypercam 183C ProTec that I bought a few months ago and was able to get out a week ago for a second round of testing.  The first time out in the beginning of October I shot two targets and and both processed fine.  This second time I shot 4 targets and no matter what I've tried I can not calibrate out the sensor glow.  I'm at a loss as to what I'm doing wrong, since it was fine the first time and I haven't done anything different in my workflow.  I even went as far as stacking the lights without any calibration frames and the result looks pretty much the same.  It's as if my darks aren't having any affect at all.

I use the normal OSC cmos workflow:  stack uncalibrated darks to masterdark, average/no normalization/don't care, uncheck evaluate noise, linear fit/no normalization.

Calibrate the lights with the masterdark with calibrate and optimize unchecked.  (I use flatdarks to calibrate the flats, then stack to masterflat, but don't really care about that at this point, the flats seem to be working fine.)

For this testing I'll debayer, register, then stack the lights.

The sensor glow is still in the calibrated light frames, you've got to really stretch it to see but it's still there.  When you stack them it becomes very evident.  I've triple checked that all the settings between the darks and lights are the same (180s/-10c/400/40/1x1).

I'm pulling my hair out trying to figure this out.  I'll attach what I'm getting and link to my google drive for the lights and darks.  Could someone give some advice as to what I'm doing wrong and/or give my data a go and let me know what you come up with and how you did it??

https://drive.google.com/open?id=1U9LMYDm7ao19N6P57jj5O7kprv7XXtPY

This is driving me crazy!

Thanks,
Scott

[bulrichl]

Hi Scott,

some questions:

1) The light frames are in XISF format. Why is it so? I would expect them in FITS format. If you manipulated these light frames, please upload some light frames in FITS format.
2) Did you use the same camera driver for capturing darks and lights?

The dark frames are captured with NINA v1.10.0.1021 at 22th October, the light frames at 22th December with NINA v1.10.0.1044.

The AD converter of the sensor, IMX183, has 12 bits (intensity range 0 - 4095). The dark frames and the MasterDark are obviously not scaled (i.e. the range of intensities is 0 - 4095). However, the light frames are scaled (range 0 - 65535). If you calibrate scaled light frames with an unscaled MasterDark, the result will be nonsense.

I don't understand why the dark frames are not scaled. This is absolutely unusual. From the given information I cannot recognize what the reason for this is; either the application of a different camera driver or the different NINA version for capturing of dark and light frames could be the culprit.

Bernd

[tristarcapt]

Hmmm Bernd, thanks for the quick response.  You may be on to something there.

First let me answer your questions:

1).  In NINA I have the option to save as .xisf so I just do that and us BatchFormatConvert if I need to change them.
2).  And yes, the Native Altair driver in NINA.

BUT, where I think you're onto something is in the bit scaling.  When I use the Flat wizard in NINA its easier to turn off bit scaling.  Perhaps I forgot to re-enable it when I shot my darks.  Let me re-shoot my calibration files with bit scaling enabled again and see what happens.

Thanks, Scott

[tristarcapt]

The AD converter of the sensor, IMX183, has 12 bits (intensity range 0 - 4095). The dark frames and the MasterDark are obviously not scaled (i.e. the range of intensities is 0 - 4095). However, the light frames are scaled (range 0 - 65535). If you calibrate scaled light frames with an unscaled MasterDark, the result will be nonsense.

I don't understand why the dark frames are not scaled. This is absolutely unusual. From the given information I cannot recognize what the reason for this is; either the application of a different camera driver or the different NINA version for capturing of dark and light frames could be the culprit.

Bernd

The bit scaling was it!  You're a genius, I wouldn't have thought of that in a million bazillion years.  I know I was doing something wrong, I just couldn't put my finger on it.

Thank You Bernd,
Scott