Help - What's wrong with my master light?

[bulrichl]

Hi Andy,

the background is somewhat dark from my point of view (slightly too aggressive black point adjustment?), but yes, this image is much better than the results before.

Whether it is worthwhile to optimize the capturing of flat frames or not is up to you. Generally, the flatfield correction is very important and it is not recommended to skip this step. Hopefully you will get some good advice in the CloudyNights thread for the capturing of useful flat frames for this special configuration (ASI294 and dual band pass filter).


I still don't understand what ImageIntegration settings have to do with the removal of amp glow. The amp glow has to be removed in the ImageCalibration step, it has to be removed from each of the light subframes. The critical point is 1. to use a matched MasterDark (gain, offset, temperature and exposure time) and 2. to disable 'Optimize'. You can check whether image calibration has made it by inspecting the individual calibrated light subframes. If this step is successful, there will be no amp glow in the integration result.

Bottomline: it is not possible to remove amp glow by tweaking the ImageIntegration settings, this has to be done before, at the image calibration stage.

Bernd

[andythilo]

Hi Bernd

I've never manually integrated in PI, I've only ever used BPP. For some reason BPP wasn't correctly removing the amp glow in this case, I tried it twice. Once I did it manually i.e created master dark, calibrated with the lights, cosmetic correction, debayered, star aligned and final integration to produce the master light it worked with zero amp glow.

My darks are from my library and matched to the lights, both 180secs, gain 120, sensor @ -20.

With regards to cloudynights, I've had no responses but I'll do my own tests of flats at various exposures/ADU values and see how they integrate. To that end, if I create a batch of different masterflats, I'll do the SplitCFA and Statistics and see what they look like.

Cheers

Andy

[andythilo]

Ok well either I'm doing something very wrong, or there's a problem with my flat field generator. So I created some new flats, all at gain 120, camera cooled to -20 and focus in same position as when I took the lights.I also created a fresh batch of BIAS files to use with the tests.

I took 30 subs each with the generator at full brightness (approx 12V), dimmed to 8V and dimmed to 5V. All at ADU values of 20000, 22000, 25000, 27000 & 30000.

I then did some stacking in DSS and PI.

All processing in PI for comparison purposes was identical, ABE and SNCR. This was just to be able to get an idea on image quality.

In DSS I ran the same sequence with all 3 voltages @ ADU3000. All 3 resulting images looked virtually identical. So I then processed in PI. I then ran the same without flats.

In PI, I did a full manual integration as per the book Inside Pixinsight, and also used the BPP script. Again with and without flats.

6 images below show the following:

Top - DSS. Left with flats, right without flats

Middle - PI BPP. Left with flats, right without flats

Bottom - PI Full Manual Integration. Left with flats, right without flats


Again all 6 processed in PI with the Automatic Background Extractor and SNCR (green).


Conclusion, my flats are broke lol. My images are 100% cleaner with no flats and manual integration without flats the clear winner with DSS a close 2nd. For some reason BPP isn't removing my amp glow. No idea why, it used to! So I'm going to send this to the flat field generator supplier and manufacturer to advise. This is the generator I use:

https://www.astroshop.eu/flatfield-masks/gerd-neumann-jr-aurora-flat-field-panel-160mm-12v/p,46378

PI_DSS_Flats_Noflats_Compare by Andy Thilo, on Flickr

[bulrichl]

The difference between the results of PI BPP and PI manual preprocessing is obviously due to your wrong settings in the 'Global Options' section of BPP: 'Use master bias' has to be unchecked, both with and without a MasterFlat.

I will not speculate about the cause of the fact that your MasterFlat doesn't correct properly, there are some more possibilities except the flat field generator. The ASI294 is a very touchy camera. Using the ASI294 I had severe problems with the "colored background artifact" (see the lengthy thread https://www.cloudynights.com/topic/596025-zwo-asi294-mc-pro/ , examples of deep integrations are in posts #105 and #112. The images show STF auto stretched integration results without any further processing). I could not manage these issues appropriately and finally threw in the towel and purchased an ASI071 which I now use exclusively. I didn't use a dual band pass filter though -- this could still complicate things.

However, in my view your results without applying a MasterFlat don't look bad at all. Certainly you should manage to remove amp glow completely. This is possible with BPP and correct settings as well as with manual preprocessing (see above).

At any rate, your issues are NOT caused by PixInsight, so I would like to finish my answers for now.

Bernd

[andythilo]

Hi Bernd

I’m not for a second blaming PI. The issues I’m having with BPP are not important, rather just just included as a query. I don’t ever use masters with BPP and leave the boxes unchecked. Why it’s suddenly not removing amp glow, I’ve no idea.

I’ll keep looking for a solution, thanks for all your help.

Andy

[andythilo]

Just to update, I had a play with WBPP this morning and with optimise dark frames disabled, it removed the amp glow fully.

With regards to the flats, I'm in touch with Gerd and funnily enough, they sell a LPR filter which combats the issues you stated at the start -

https://www.gerdneumann.net/english/astrofotografie-parts-astrophotography/aurora-flatfield-panels/aurora-accessories-aurora-zubehoer/lpr-konversionsfilter-fur-100mm-und-160mm-aurora.html

However I still think there's a problem with my panel because of the dark streak and mottling in the flat images.

[bulrichl]

As a general rule, when using a camera with a CMOS sensor that exhibits amp glow, dark frame optimization should NOT be used, otherwise the amp glow will not be removed completely by subtracting the MasterDark. That means, the option 'Optimize' has to be disabled in section 'Master Dark' of ImageCalibration (of course the same holds for the option 'Optimize dark frames' in 'Global Options' of BPP or WBPP). I had told you my settings for ImageCalibration already in reply #13 of this thread and therefore did not suppose that you used different settings.

Since it is such a small investment, it would not hurt trying the LPR conversion filter, but i am not optimistic. If you decide to purchase it, I would be interested to see a MasterFlat with it and a full calibration result (with MasterDark and the new MasterFlat). Good luck!

Bernd

[andythilo]

It was my darks. My darks had really bad light leaks, highlighted to me by someone on Cloudy Nights. I retook my 180s darks by putting the camera in my fridge with it's cap on and halfway in it's bag.

Result:-

[bulrichl]

OK, I was on the wrong track concentrating only on the flats. I am glad that you were able to solve this issue, and that the correct calibration procedure (using dark frames, flat frames and flat-darks) results in a flat integration result -- just as it should be.

Bernd