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ZWO ASI294 MC pro

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#151 Jon Rista

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Posted 02 June 2018 - 11:06 AM

According to your suggestion I just debayered my calibrated data as well with the Bilinear as with the SuperPixel interpolation method. The result is: It makes no difference in respect to the colored background artifact in the resulting integration.

 

I never tried bayer drizzle, so I have no experience how to apply it to my data.

 

I don't quite understand this statement. I never used an output pedestal and didn't experience any drawback so far. When my light frames are calibrated with my 150 s MasterDark and the MasterFlat, there is no severe clipping to zero. I have checked this again: with the set of 95 calibrated light frames the average number of pixels that are clipped to zero is 29 pixels. Given that the sensor has 11.7 million pixels, this is negligible. I can only imagine that you are referring to the wrong MasterDark (300 s) that I uploaded by mistake in the first zip archive. The 300 s MasterDark indeed could have produced some clipping when applied to the 150 s light frames.

 

Anyway, I did as you suggested and performed the workflow with an output pedestal of 800 DN applied. Again there was no visual difference in the integration result, and their histograms (workflow with / without pedestal) are barely discernable. So this is also not the cause of the colored background artifact.

 

Bernd

Definitely not the wrong dark. I created a new dark from the 150s frames, then used that new master to calibrate each of the same 150s frames. Without a pedestal, they did not calibrate properly. I would try using a pedestal when calibrating your lights and see if it changes anything. 


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#152 glend

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Posted 02 June 2018 - 11:39 AM

Jon, surely your not suggesting that this camera can only be useful to people that use PI? There are many of us that do not use PI, nor understand pedestals and other PI references. If this camera cannot he calibrated without exotic steps then there is something seriously wrong with the camera. I can't recall another ZWO camera that is this much trouble. Perhaps QHY can get theirs right, or maybe this chip is just not AP material.


Edited by glend, 02 June 2018 - 11:40 AM.


#153 bulrichl

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Posted 02 June 2018 - 11:48 AM

Definitely not the wrong dark. I created a new dark from the 150s frames, then used that new master to calibrate each of the same 150s frames. Without a pedestal, they did not calibrate properly. I would try using a pedestal when calibrating your lights and see if it changes anything. 

 

Yes, but as I wrote,

 

Anyway, I did as you suggested and performed the workflow with an output pedestal of 800 DN applied. Again there was no visual difference in the integration result, and their histograms (workflow with / without pedestal) are barely discernable. So this is also not the cause of the colored background artifact.

I already did it. I applied the MasterDark "MasterDark_110_150s_-15.xisf" in the second zip file and an output pedestal of 800 DN. These were the settings in the ImageCalibration:

 

Pedestal_800.JPG

There was no significant difference in the resulting integration result.

Can you please upload the MasterDark that you created from my dark frames?

 

Bernd

 

 

 

 

 



#154 bulrichl

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Posted 02 June 2018 - 12:01 PM

OK, I guess now I understand what is going on. I sent only 25 dark frames in the zip file. However, my MasterDark is built from 110 dark frames. Therefore, the peak in the histogram of your MasterDark will be much broader than of that of my MasterDark. So you have to apply an output pedestal in order to avoid clipping whereas I don't have to.

 

Why didn't you try my MasterDark? It is in the second zip file.

 

Bernd


Edited by bulrichl, 02 June 2018 - 12:03 PM.


#155 Jon Rista

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Posted 02 June 2018 - 12:31 PM

OK, I guess now I understand what is going on. I sent only 25 dark frames in the zip file. However, my MasterDark is built from 110 dark frames. Therefore, the peak in the histogram of your MasterDark will be much broader than of that of my MasterDark. So you have to apply an output pedestal in order to avoid clipping whereas I don't have to.

 

Why didn't you try my MasterDark? It is in the second zip file.

 

Bernd

I tried yours as well. I created one of my own, and used yours. Same result with both. It isn't the number of frames or the dispersion of the noise. 

 

Anyway, if you already tried a pedestal, and it did not work, then that's that. I thought you said you tried superpixel and it didn't help.



#156 Jon Rista

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Posted 02 June 2018 - 12:36 PM

Jon, surely your not suggesting that this camera can only be useful to people that use PI? There are many of us that do not use PI, nor understand pedestals and other PI references. If this camera cannot he calibrated without exotic steps then there is something seriously wrong with the camera. I can't recall another ZWO camera that is this much trouble. Perhaps QHY can get theirs right, or maybe this chip is just not AP material.

A pedestal is simply a fixed offset added to each pixel before subtracting the dark. It is not a PI thing, it is actually a term that has been in use for decades, and even has a FITS header for it. I am pretty sure PI is not the only program that can add a pedestal. I don't know if DSS can do it, but there is also MaxIm, ImagesPlus, APP, Nebulosity, etc. I know that APP has some pedestal options. I would be surprised if MaxIm DL did not. 



#157 bulrichl

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Posted 02 June 2018 - 01:01 PM

I tried yours as well. I created one of my own, and used yours. Same result with both. It isn't the number of frames or the dispersion of the noise. 

 

Anyway, if you already tried a pedestal, and it did not work, then that's that. I thought you said you tried superpixel and it didn't help.

Yes, separately from the workflow with an output pedestal applied, I also tried bilinear and superpixel interpolation methods as well - but that didn't help either.

 

Yet I have an idea for light frame acquisition that I will try tonight. However, it's just a straw...

 

Bernd



#158 sharkmelley

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Posted 06 June 2018 - 12:21 AM

Hi Bernd,

 

As you know, I hit a purple/green background artifact problem with my Sony A7S:

https://www.cloudyni...egreen-swathes/

 

This may be the same issue you are hitting with the ASI294, or maybe not.  In any case, I have not yet found a solution to the issue.

 

There is one thing you can try to help to demonstrate the problem.  Try creating a well exposed master flat and then another couple of master flats at different levels of exposure.  Now use each master flat to calibrate the others.  In my case (see the thread above) I ended up with a changing pattern of stripes which is evidence there is some kind of overall calibration issue with the Sony A7S.  If master flats cannot calibrate each other then this is clearly an issue for deep sky astrophotography because such behaviour violates the usual calibration assumptions.

 

I strongly suspect that it is due to some "clever" on-sensor internal processing.

 

Mark


Edited by sharkmelley, 06 June 2018 - 12:22 AM.


#159 tjugo

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Posted 06 June 2018 - 12:49 PM

Hi Bernd,

 

As you know, I hit a purple/green background artifact problem with my Sony A7S:

https://www.cloudyni...egreen-swathes/

 

This may be the same issue you are hitting with the ASI294, or maybe not.  In any case, I have not yet found a solution to the issue.

 

There is one thing you can try to help to demonstrate the problem.  Try creating a well exposed master flat and then another couple of master flats at different levels of exposure.  Now use each master flat to calibrate the others.  In my case (see the thread above) I ended up with a changing pattern of stripes which is evidence there is some kind of overall calibration issue with the Sony A7S.  If master flats cannot calibrate each other then this is clearly an issue for deep sky astrophotography because such behaviour violates the usual calibration assumptions.

 

I strongly suspect that it is due to some "clever" on-sensor internal processing.

 

Mark

Mark,

 

Very interesting. I will create a couple of master flats with different exposures and see if they calibrate out between each other.

 

Amazing that you are the only one reporting this issue with the Sony A7S, I guess most people simply get rid of the background artifact with photoshop or they simply don't care :(

 

I will post my results tonight!

 

Cheers,

 

Jose


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#160 ChrisWhite

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Posted 08 June 2018 - 06:28 AM

Mark,

 

Very interesting. I will create a couple of master flats with different exposures and see if they calibrate out between each other.

 

Amazing that you are the only one reporting this issue with the Sony A7S, I guess most people simply get rid of the background artifact with photoshop or they simply don't care frown.gif

 

I will post my results tonight!

 

Cheers,

 

Jose

 

What did you end up seeing?



#161 AdamJ

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Posted 08 June 2018 - 08:06 AM

With Sony I would not be at all shocked if it turned out that raw was not really raw and it was doing some sort of calibration every time you power the chip etc. 



#162 tjugo

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Posted 08 June 2018 - 11:54 AM

Mark,

 

Very interesting. I will create a couple of master flats with different exposures and see if they calibrate out between each other.

 

Amazing that you are the only one reporting this issue with the Sony A7S, I guess most people simply get rid of the background artifact with photoshop or they simply don't care frown.gif

 

I will post my results tonight!

 

Cheers,

 

Jose

Hi,

 

These are some master flats created with different exposures times, 1s and 5s. A flatman screen with controllable brightness was used to for the capture. The histogram of the flats had 3 humps, the green hump was ending close to 30k ADU. The red and blue humps were close to 11k ADUs. The flats were calibrated using 64 darks of the same exposure time per set. The master flats were created by integrating 64 individual flat frames per set.

 

I am also attaching an uncalibrated 60s light frame. I calibrated it just using the master flats and it looks like the master flat overcorrects the light frame.

 

Feel free to download and play with the images. They were

 

Calibrated 5s master flat:

https://drive.google...ld_Hd5xJKFJGBvl

 

Calibrated 1s master flat:

https://drive.google...A_jj7Y9oPretAES

 

Uncalibrated 60s raw light of M13

https://drive.google...Ml5mZQ5S6BUPHnr

 

Cheers,

 

Jose



#163 tjugo

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Posted 08 June 2018 - 04:13 PM

This is the histogram of an individual flat frame:

 

histo.jpg



#164 tjugo

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Posted 08 June 2018 - 04:16 PM

This is an integration of 88 x 1 min exposures. The images were dithered and calibrated with 128 x 1min darks and the master 5s flat frame.

 

The image is heavily stretched to show the uneven background.

 

backgrous.jpg



#165 sharkmelley

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Posted 08 June 2018 - 06:10 PM

This is an integration of 88 x 1 min exposures. The images were dithered and calibrated with 128 x 1min darks and the master 5s flat frame.

 

The image is heavily stretched to show the uneven background.

 

 

Has the master flat been bias subtracted?  If the lights were calibrated with darks but the flats are not calibrated then of course undercorrection or overcorrection will occur (depending on whether the flats are more exposed or less exposed than the lights).

 

Do you have the master bias?

 

Mark


Edited by sharkmelley, 08 June 2018 - 06:21 PM.


#166 andysea

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Posted 08 June 2018 - 06:13 PM

That looks very similar to the artifact that I am getting on my images.

#167 DonBoy

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Posted 08 June 2018 - 06:32 PM

I'm wondering if any meaningful tests can be made without cooling too see if these gradients are present in a similar manner.


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#168 tjugo

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Posted 08 June 2018 - 08:00 PM

Has the master flat been bias subtracted?  If the lights were calibrated with darks but the flats are not calibrated then of course undercorrection or overcorrection will occur (depending on whether the flats are more exposed or less exposed than the lights).

 

Do you have the master bias?

 

Mark

I calibrated the flats using a master-dark-flat, I created the master-dark-flat with 64 images of the same exposure time as the flats. I am not using bias, I am only using darks and darks-flats for calibration.

 

Cheers,

 

Jose



#169 tjugo

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Posted 08 June 2018 - 08:01 PM

The camera cooler was set to 0C (around 30% duty cycle)

 

Cheers,

 

Jose



#170 andysea

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Posted 08 June 2018 - 08:14 PM

I'm wondering if any meaningful tests can be made without cooling too see if these gradients are present in a similar manner.

Yes! I can’t believe I hadn’t thought of that. We should take a series of subs with no cooling then stack them with no darks and see if the artifact is there.
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#171 AhBok

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Posted 08 June 2018 - 09:24 PM

That looks very similar to the artifact that I am getting on my images.

And me as well. I am able to deal with mine in post, but it would sure be nice to not have to deal with this every image.



#172 jgraham

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Posted 09 June 2018 - 08:48 AM

Hmmm, do you notice it during 'normal' processing, or do you often stretch your images hard enough to see it. I have not noticed anything like this in my images, but then again I try to limit the use of aggressive curves. I also have a method for synthetic flats in Photoshop that is so quick'n easy I don't think about it much. If I have an odd gradient I just take it out. Easy peasy. This might be a bigger deal if I were imaging under very dark skies where I could see some of the really faint, diffuse background features, but from my back yard that it very uncommon. I did get a peek at the Antares/Rho Ophiuchus cloud a while back though, but that's rare.

 

Neat stuff.



#173 Shiraz

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Posted 09 June 2018 - 09:44 AM

how do you guys provide the IR blocking filter that this thing probably needs - it doesn't seem to have one built in? 

 

Clutching at straws, but could that be part of the cal problem?


Edited by Shiraz, 09 June 2018 - 09:44 AM.

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#174 bulrichl

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Posted 09 June 2018 - 10:34 AM

how do you guys provide the IR blocking filter that this thing probably needs - it doesn't seem to have one built in? 

 

Clutching at straws, but could that be part of the cal problem?

 

I use an "Astronomik L Typ 2c" filter ( https://www.astronom...3.html?size=134 ). The filter is mounted at a distance of about 51 mm from the sensor.

 

Bernd



#175 jgraham

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Posted 09 June 2018 - 12:21 PM

Ahah! That could very well be it, or at least a contributing factor. I haven't been able to find response curves for the ASI294MC Pro that go all the way out to the IR, but the chip used in the ASI071MC Pro begins to show some response out in the near IR, giving color response where there is none. The fix is to install an IR cut filter in the nose piece. I bought a nice economical IR filter from Highpoint Scientific. Also, most light pollution filters also cutoff in the near IR. I use an Orion Imaging Skyglow Filter for DSO imaging, and the Highpoint IR cutoff when taking photometric images. An IR filter will also help keep your sensor clean.

 

Something to try.




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