ASI 6200MC Pro - dark calibration issue

ewelot

Hi,

first of all thanks for providing this forum and offering this very kind level of support which is much appreciated!

I have joined in to get some help/advice on using my new ASI 6200MC Pro camera which otherwise fits extremely well on my Celestron RASA 11" scope.

The problem I am facing is related to dark subtraction: it appears that a considerable amound of pixels is not well calibrated and appears brighter than the average background.

Here is the details about my images:

masterdark:

- capture of 48 exposures at 60 seconds each

- processing: average (and median) of all images

bayered light:

- capture of 25 exposures of a star field at 60 seconds each, guiding on star (only in RA)

- processing: each image is subtracted by a masterdark and divided by (flatdark subtracted and normalized) masterflat, followed by average of all images

- note that there has been no debayering (interpolation) applied

enhanced (bayered) light:

- same as above but in addition subtracted by an average bayer pattern (for enhanced visibility of artifacts)

I have been using the following camera settings:

Gain=0, Offset=20, WB_R=50, WB_B=50, Sensor Temperatur=-5 °C, Binning=1x1

The given example images are cropped at center area of ~200x200 pixel.

It should be noted that the intensities of the bright deviating pixels is not random, they are almost all within 100-300 ADU above background. This distribution is unlike that of thermally induced hot/warm pixels. It appears similar on other light image sets but not identical. Do you have any idea about the origin of these artifacts and how to prevent them?

Thanks,

Thomas

masterdark.pnglight_bayer.pnglight_bayer2.png

Support@ZWO

Hi Thomas, please make sure the light and darks are using the same settings including offset, temp, exposure time, and other specs.

And could you send an email to support@zwoptical.com and share us the fit file via Google Drive or dropbox link? We may try to calibrate it.

ewelot

Thanks for your reply!

Yes, darks and lights are using the exact same settings including gain, offset, sensor temp, exposure time and others.

I' am sending you a couple of darks and lights (actually crops of the same region) for further inspection in a few minutes.

Thanks for help,

Thomas

Support@ZWO

Please check the settings again, you can try test it with ASIStudio.

ewelot

May I kindly ask what you mean with "check the settings again"?

Do you mean that my settings - as reported in the original post - are not a recommended setup?

Do you suspect that settings differ between dark and light frames? I can ensure that I have double checked they are the same.

Could you please provide a more specific hint on what is (possibly) wrong with my setup and which measure I could take to solve the issue?

Thanks,

Thomas

Support@ZWO

Hi Thomas,

We suspect the light and darks setting is different.

Could you test capturing images in ASIIMG?

ewelot

I have captured new images using your ASICap software, as requested. You can download the raw FITS files from here. The archive comprises of 15 dark images followed by 15 lights, all covering a 1000x1000 pixel area in the center of the camera sensor.

My own analysis is showing the exact same behavious as described in the original post, which is expected because I have been using the exact same camera settings. Anyway the capture with ASICap went very smoothly (on a Linux desktop running Debian 10) and is useful for testing purposes as it reveals all camera settings within the FITS file header for later reference. Thanks for providing this software.

Best regards,

Thomas

Support@ZWO

Hi Thomas,

Normally this can be calibrated, please take more calibration subs and try calibrating it.