ASI2600 Darks Problem

C

chromesurfer

Member
I just upgraded to the new 2600MC and I'm having problems with processing when I include my master darks. I've used my manual pre-processing routine that worked fine for me with my ASI071MC and ASI1600MM, but when I get to the end of preprocessing (after debayering), I'm left with an image that has '0' RGB background values, which after stacking and integrating leaves me with nothing to work with. I've discovered by trial and error that if I leave the dark out of the calibration process, it seems to work fine using only bias and flats.

I thought maybe my process was off, so I tried putting the files through the new WBPP2 script, but I get the same results.

I've heard that maybe the darks are not needed for this camera due to low dark current, but I'm not sure how to validate other than it seems to work for me. Has anyone else experience issues in using this new camera?

Thanks!
 
I do have the same camera. Until now at gain 100, offset 5, minus 10 degrees

With my latest photo I also had a problem with my darks, but then I took new ones, and now all is fine, using the workflow of Bernd, of course.
The ones I used first were at -5 degrees and not -10. I suppose that is the reason.

I'm also wondering if they really add something. Did some testing and offset 5, gives values between 50.9 and 51.2. As you certainly know, offset 5 gives a base ADU of 50.

This is the photo that gave first some problems, but now is ok : http://www.fotografiepieter.be/207-messier-101
 
I'm using 30sec subs with 100 gain, offset 50. Attached current preprocessing settings screenshots.
 

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  • Flats Integration.png
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Yes, that worked. MasterBias and MasterDark are looking well. However, I would need say 4 light frames in FITS format.

Bernd
 
The median of the MasterBias is 500.967, of the MasterDark 501.099 and for the light frames in the range of 347 to 380.5. This means: the master calibration files do not match the light frames.

According to the FITS headers, light, bias, dark and flat frames were captured at a gain of 100 (correcponding to a conversion gain of 0.243 e-/ADU).

I use an ASI2600MC Pro myself, so I know that your dark and bias frames were captured with the offset default setting of 50, causing a shift of 500 ADU in the frames.

The obvious reason for the deviating, much too low medians of the light frames is that they have been captured at a lower offset setting.

From the histograms I estimated that the shift in the light frames is only 100 instead of 500 ADU, corresponding to an offset setting in the camera driver of 10. So I did a manual calibration in PixelMath, correcting the normal calibration result by 400 ADU:

RGB/K: ($T-ASI2600MCMasterDark0C30sec+p/65536)/Master_Flat*mean(Master_Flat)
Symbols: p=...

The result with p=400 still looked slightly undercorrected, so I tried p=450 (this corresponds to a shift of 50 ADU and an offset setting in the camera driver of 5). To me, the latter result looked like a well calibrated light frame. Please note that this is only an approximate correction. The above PixelMath expression can be used with the present light frames of M 81 using an ImageContainer.

The appended JPG is the integration result from 4 of your subframes:

M81.JPG


Did you change the offset setting for these light frames? If you know that value, use in the PixelMath expression the true correction value p that arises from that setting, namely:

p = (50 - offset) * 10 ADU

For the future, the question is: do you want to use the default offset setting of 50 or a reduced value? In the latter case you have to capture new calibration frames with that reduced offset setting. However, the improvement of dynamic range is negligible when reducing the offset setting, so I advise against it. For new projects, I would use the default offset for the lights and use the master calibration files on hand.

Bernd
 
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Hi Bernd. Thanks so much for educating me on this. My intention was to stay with the 100 gain / 50 offset, which is what I thought all my pics were taken with. I just checked my SGPro ascom setup and sure enough, the gain was 100, but the offset was '1'. I'm pretty sure I checked and set it to 50, but somehow it must have gotten reset. Thanks for pointing this out to me.

I'll re-calibrate the files using the pixelmath and process this batch, but the rest of my pics will be 100/50 in the future.

JW
 
Hi.

I wanted to ask this already, but prefered to wait until your original question was solved.


May I ask why you choose an offset of 50 (giving 500 extra ADU) for this camera ?
For the moment I am using offset 10, at gain 0 and gain 100, and minus 10 degrees temperature.


I suppose the raison for offset 50 is to avoid any dark pixels while calibrating ?

And do you have an indication/proof that that would be the case at offset 10 ? If I look with the histogram transformation it even seems to me that offset 7 or 8 would be enough. Maybe is that because my camera is still "brand new" (three months old) ?

Thanx in advance for your considerations...
Pieter.
 
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Hi Pieter - I went with offset 50 because that appeared to be the default when you put the camera in high-gain mode (100+). I originally used the ASI application to generate my darks/bias frames and it defaulted at 50 when I used it so I stuck with that. Sorry it wasn't as scientific as you thought. Based on what I've heard, adjusting the offset on this camera doesn't really result in much change as long as you match it up with your light frames.

JW
 
okidoki ! You are not the only one coming up with the offset 50, I've seen that before. And now the mystery has been unraveled ! Thanks for that !

The matching is indeed important... In fact, I evoluated from gain 100 Offset 5 to gain 0, offset 10.
And this because that setting seems to have less problems with the fat star syndrome that I had to fight with M101 (and now M51). I did conclude that through some testings myself. (my scope is a 130mm refractor, f5.6)

But being always interested in the reason why something is done, I was curious about your settings...
 
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