Ha test with poor r...
 
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The problem with the data upload limit for attachments has been fixed. I have restored it to 30MegaBytes. A recent forum software upgrade was responsible for the changed limit. Please accept my apologies for missing this when upgrading the forum sofware, Mabula.

Ha test with poor results  

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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
15/02/2019 11:16 am  

Hi,

last night while waiting for The Moon to clear my viewpoint I thought I'd try out some Ha imaging but I am not very happy with the resulting integration.

I understand that only 3 Light subs is not going to give me the best or anywhere near the best result but the problems with this stack is more than that & I could do with some guidance.

Also I know that using NB filters with a colour camera will not let them shine to their full ability.

This was my 1st attempt to image using my NB filters & aside from the expected vignette on the Lights, individually they seemed to look OK.

I was also using Dither for the 1st time in BYEOS between each Light capture.

On previous occasions during imaging I had not used Dither and noticed resulting stack noise was bad and read that Dither will help alleviate this.

Here is the integration:

 

Horsehead Ha Test

 

Here is my setup:-

EQUIPMENT

Celestron CPC9.25

Celestron f/6.3 Focal Reducer

Canon EOS750D modded

Baader 48mm H-alpha 7nm filter

 

CAPTURE SOFTWARE

BYEOS

PHD2

 

DATA

LIGHTS - 3 x 1200s @ ISO800

DARKS - 5 x 1200s @ ISO800

FLATS - 10 x 2.5s @ ISO800 (captured with lightpanel)

MB - 100 x ISO800

BPM

 

To me the integration shows clearly that the vignetting has been over-corrected but the Flats that I have taken, I have made in the usual way that I do when capturing non NB subs.

The image also shows horizontal banding and I have a strong suspicion that this is from my lightpanel used in Flats capture.

Also the resulting image is very, very noisy with a lot of detail lost compared to the captured Lights.

Could this all be down to dithering?

Here is my full data on DropBox [747mb]:  https://www.dropbox.com/sh/cjdvve1yupuuswk/AAAwJuCuXQWBA5Zly0n50Zy8a

Regards..,

Kirk

 

 

 

 

This topic was modified 6 months ago by Mabula Haverkamp - Admin

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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
22/02/2019 11:24 am  

I am still struggling with this issue.

While I had some clear sky last night I decided to try another test.

I understand that this image is lacking due to the fact that I was only able to capture 4 Light frames but it does some the issue.

Firstly here is one of my Flats shown in Linear form with DPP off & Black Point is Zero as per:  https://www.astropixelprocessor.com/community/faq/dslr-how-to-check-the-linear-histogram-of-your-data-or-how-long-can-i-expose-my-flats/

 

Linear Flat

 

You can see that the Histogram is pretty good. Now here is my Integration

 

Integration

 

It is obvious that there is something very wrong with Flat correction or a step that I am missing somewhere. It is somewhat familiar to the error in a previous version of APP:  https://www.astropixelprocessor.com/community/main-forum/raw-files-for-processing-practice/paged/2/#post-2940

There is another thread about it here too:  https://www.astropixelprocessor.com/community/main-forum/master-flat-is-over-correcting/

 

Now I am trying my data once again but this time with a fresh set of Bias frames as currently I have been using a previous generated by APP, MB & BPM

 

So for the above image my data is:

4 x 900s ISO800 Lights [Ha Filter] (Canon EOS750D modded)

10 x 2.5s ISO800 Flats [Ha Filter] (Canon EOS750D modded)

8 x 900s ISO800 Darks (Canon EOS750D modded) Temp matched to Lights

MB ISO800 x 100 subs & BPM .fits previously generated in APP and been using these fine up until recently.


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
22/02/2019 11:42 am  

OK, I just ran my data again but using a new set of Bias (70 frames) to create a new MB & BPM. The result was exactly as previously with the Flat vignette appearing white/pale.

Here is a RAW Light Frame: 

Raw Frame

Here is that same frame once Calibrated:

Calibrated Frame

Here is the resulting Integration after using a new MB & BPM:

New Integration


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
23/02/2019 11:39 pm  

I've spent most of the day today attempting to get to the bottom of this issue but found no resolution.

Looking at my Flats as Linear with DPP off & Black Point at 0, my ISO800 2.5s frames are the max I can get before hitting the right side of the histogram in APP.

Just for the sake of it I tried other iterations with Flats sets of 1.3, 1.6, 2.0, 3.2 & 4.0 seconds.

Anything up to and including 3.2s basically looked identical in the final Integration but 4s was decidedly worse with far more negative vignette showing.

I am now completely stumped and cannot progress any further using NB filters until I get this somehow resolved.

@mabula-admin if you could shed some light on my issue please.

Regards.., 


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
24/02/2019 6:28 pm  

Hi Kirk @1cm69,

I will download your data right now and have a look 😉

Hang on,

Mabula

This post was modified 6 months ago by Mabula Haverkamp - Admin

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
24/02/2019 6:34 pm  

Dear Kirk @1cm69,

So this is with OSC data, right, what happens if you process the data with the Ha-debayer algorithm in 0) Raw/FITS ?

This should leave you with the monochrome calibrated Ha-data.

Your flats should have been shot with the same optical train, so with your H-alpha filter, right?

Then you can't expect the Green and Blue channels to be of any good I think after flat-field calibration. These channels will get no light when you create the flats due to the H-a filter. So you should disregard anything happening in the green and blue channels 😉

Will report back when the download is finished...

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
24/02/2019 6:41 pm  

Hi Kirk @1cm69,

Your data does not contain either bias or flat darks to subtract the bias pedestal from the flats... this is critical, so that should explain your problem.

APP will warn you that something is wrong with flat-field calibration 😉 due to missing bias/darkflats.

At least add some bias with the same gain/iso as the flats 😉

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
24/02/2019 6:51 pm  

Hi Kirk @1cm69,

In response to

To me the integration shows clearly that the vignetting has been over-corrected but the Flats that I have taken, I have made in the usual way that I do when capturing non NB subs.

The image also shows horizontal banding and I have a strong suspicion that this is from my lightpanel used in Flats capture.

Also the resulting image is very, very noisy with a lot of detail lost compared to the captured Lights.

Could this all be down to dithering?

No, any dither will only improve the integration results and will never cause the problem that you face here. This is a fundamental calibration issue due to missing calibration data to be able to subtract the bias pedestal from the flats... 😉 Only darks for the lights is never sufficient to get proper (read optimal) flat-field correction.

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
24/02/2019 6:54 pm  

Hi Kirk @1cm69,

This is what I get with the H-alpha debayer algorithm and missing bias/darkflats... it is not bad, but with at least bias it will certainly be better. The vignetting is not totally corrected :

Kirk Without Bias Or Dark Flats

Cheers,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
24/02/2019 7:02 pm  

Hi Kirk @1cm69,

I have had a look at your flats as well. Please look at the resulting masterflat in both RGB and H-a debayer:

Kirk MasterFlat RGB stretch
Kirk MasterFlat HaDebayer stretch

It does not look like perfect flats at first glance, the bottom illumination might be bad, but perhaps this is the mirror chamber in your canon dslr, it usually looks differently though, only a small darker border at the bottom is usually seen, so there might be an issue with the flats as well.

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
25/02/2019 4:32 am  

Hi Mabula,

thanks for looking at my problem. 

I was indeed using Bias as a premade MB must have forgotten to upload it with the rest, I’ll do that later. 

The odd vignetting in the Flats is due to the prism in my OAG. 

All taken with same optical train and using Canon DSLR

I very much appreciate your help here Mabula 😉

This is the first time using my Ha Filter with my dSLR and didn’t know/think about the extra step of debayering.

 

regards..,

Kirk

This post was modified 6 months ago by 1CM69

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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
25/02/2019 10:00 am  

Hi Mabula @mabula-admin,

OK, just got home and in front of my PC.

First I double checked the DATA set that I uploaded to DropBox, there is a directory named 'Other Calibration Files' in there are the MB & BPM.

Anyway, I ran through my HorseHead data just to stage '2', using Ha Alogorithm from stage '0' and it's great. That is all that I was missing, here is a screen shot:

 

HH Ha

Regards..,

Kirk


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
25/02/2019 10:06 am  

Here is the Whale Galaxy with my limited data so far:

 

WG Ha

 

On this one I am still seeing very, very faint lightness along the bottom and the two top corners but it is far better than previously.

Regards..,

Kirk


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
25/02/2019 10:31 am  

OK, I just tried to stack my Whale Galaxy data and also my HorseHead data & got this screen on both occasions, they both did stack before I used the Ha Algorithm option:

 

WG Ha Stack

 

I think that I have tried all variations of the options listed in the message box to get the Lights to Reference but it keeps failing, any ideas?

Here is the full Whale Galaxy Data Set too: https://www.dropbox.com/sh/3cgc2orooiy2ybp/AADrYf9fs84hG1TOG13iOHhfa

Regards..,

Kirk

This post was modified 6 months ago by 1CM69

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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
25/02/2019 11:07 pm  
Posted by: 1CM69

OK, I just tried to stack my Whale Galaxy data and also my HorseHead data & got this screen on both occasions, they both did stack before I used the Ha Algorithm option:

 

WG Ha Stack

 

I think that I have tried all variations of the options listed in the message box to get the Lights to Reference but it keeps failing, any ideas?

Here is the full Whale Galaxy Data Set too: https://www.dropbox.com/sh/3cgc2orooiy2ybp/AADrYf9fs84hG1TOG13iOHhfa

Regards..,

Kirk

Hi Kirk @1cm69,

So it did work and then it did not ? Do I understand this correctly?

Do you know what you changed in between? (I think I am not quite following you here, so please be as specific as you can 😉 )

I'll download the Whale data and I will check, hopefully tomorrow, and will let you know what I'll find.

Thanks,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
25/02/2019 11:18 pm  

Hi Mabula,

both sets of data integrate perfectly without any errors when using the default algorithm ‘adaptive airy disc’ but when I try to integrate either of the two datasets after using the ‘Hydrogen Alpha’ algorithm, they each fail on step 4 ‘Reference’ and show the error message as I’ve posted. 

Oddly the star count on the Horsehead subs for instance show as more than 200 after upping the level in step 3. 

By the way, I am using v1.071

Regards..,

Kirk


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
02/03/2019 9:39 pm  

Hi Mabula,

did you get the data to integrate at all without throwing the error screen?

Regards..,

Kirk


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
02/03/2019 10:50 pm  

Hi Kirk @1cm69,

Apologies, I should have time tomorrow to address your issue and will let you know my findings and possible solution 😉

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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(@1cm69)
Neutron Star Customer
Joined: 2 years ago
Posts: 132
02/03/2019 10:56 pm  
Posted by: Mabula Haverkamp - Admin

Hi Kirk @1cm69,

Apologies, I should have time tomorrow to address your issue and will let you know my findings and possible solution 😉

Mabula

OK, no problem 😉

Kirk


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(@mabula-admin)
Quasar Admin
Joined: 2 years ago
Posts: 2120
04/03/2019 4:23 pm  

Hi Kirk @1cm69,

I have found the issue with your data yesterday. Another APP user, @andersstange, also experienced difficulties with star analysis and registration and his issue was directly related. It turned out that hot pixels were detected as stars and not the stars. To solve this issue, I have added a new algorithm in the star analysis module that is capable of better discrimination between hot pixels and stars 😉

So the good news is that APP 1.072 will have the solution to this problem. All the testdata that I have including the data of you both work now robustly (without problems).

https://www.astropixelprocessor.com/community/release-information/astro-pixel-processor-1-072-preparing-next-release/

at the bottom:

  • FIXED, IMPROVED, STAR ANALYSIS, star detection has been further improved by adding an algorithm that better discrimates between hot pixels/small FWHM stars/big FWHM stars. Some users experienced difficulties because hot pixels were detected as stars. The added algorithm studies the star size/FWHM distribution initially found. The details of the distribution are very usefull to make the discrimination between hot pixels/small FWHM stars/big FWHM stars.

I will try to release APP 1.072 within 1-2 days now 😉

Kind regards,

Mabula

Main developer of Astro Pixel Processor and owner of Aries Productions


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