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DBE Question

RichardM
edited November 2022 in PixInsight
I'm going thru all your helpful DBE videos and trying to apply them to my latest image NGC 129 in Cassiopeia.  As you point out in your videos the key thing is identifying what's going on. (ie. flat-field, gradient, dust donuts, etc.)  I believe this is a flat-field error.  That said, regardless of the settings I select for tolerance or shadows relaxation, I'm not able to remove the circular glow in the upper right of center.  I've tried multiple tolerance levels from 5 to 10.  I've tried both division and subtraction.  

Can you advise as to what you think is going on?  Inn link below is he original RGB image and the second is a more processed image. (ie. PCC, SCNR, HT, NoiseExt).  


Thanks Much!


Comments

  • BlockHeadBlockHead
    Hi Richard,

    At the moment I am desperately trying to recreate FastTrack  (which everyone should review once I am done) as well as an explainer for SPCC... I am working non-stop this weekend. I probably can't get to this immediately... but that being said... you will need to make the file permission available to anyone that has the link. Currently only you can see the file.

    Thanks,
    -the Blockhead

  • RichardM
    oh, ok, thanks for the heads up! I'll reset it...
  • RichardM
    https://drive.google.com/drive/folders/1nQZWKt0g58aQcAuUWvImu6SagKowXvLE?usp=sharing

    Thanks! I have reset so anyone should be able to see the two files.  No hurries!
  • BlockHeadBlockHead
    Hi Richard,

    This image is puzzling. 
    First, unfortunately it isn't possible to figure out the puzzle by looking at the integrated image. We would need to examine all of the raw data and their masters to start to figure it out.

    One thing that bothers me is that this bright star has diffraction in just one direction. Can you explain that? It looks like an obstruction... or maybe clips of a refractor? I am not certain what equipment you are using. 

    Second... IF that is a flat field error it is really bizarre. The fact that it is so offset makes me think something is not aligned. Perhaps as if the camera and items behind the telescope is not aligned with the output of the telescope... or something.

    So, I can't say what is going on- but I am pretty certain this is not the kind of thing to accept and chase down with DBE. Instead, I think more needs to go into figuring out how things are being illuminated and calibrated.

    -the Blockhead
  • RichardM
    Thanks Adam,

    I totally agree that I should diagnose the underlying causes of these issues first as opposed to using PI to fix them. And I have been trying to do so for a while as I’ll describe below.

    I’m using a 9.25” Celestron SCT, HyperStar with an Optolong LP filter, and ZWO294MC Pro on a Skywatcher mount. I don’t do anything particular with the cables other than just let them hang down (and I wonder if that could be an issue for diffraction). I use Asiair for capturing.

    Additionally, I take all my frames from my Detroit-based condominium courtyard where there are a lot of lights so I use a flexible due shield on the scope to help block stray light. The LP Bortle rate where I am is 7.

    Next week I’ll post some of the raw light frames: (calibrated, debayered) as well as some of the darks, flats, dark flats. I typically shoot either 30 sec or 60 sec frames for lights. I use master darks that correspond to those exposure rates (or in some cases I may do new darks after the session).

    I have been struggling with making and diagnosing effectiveness on my flats. I use a light panel from Germany on top of the dew shield but I have to use light filters to get the ADUs down to the correct range even with low settings on the panel. My camera is the ZWO 294MC pro CMOS and they (and others) recommend using at least 3 sec exposures on the flats to account for the “flashing” that occurs in the corner. I have a library of dark flats that I’ll use either with 3 sec or whatever other exposure rates I’ll try on the flats. I’ve been doing a lot of trial and error by varying the levels of ADUs by changing the exposure rates of my camera and intensity levels on the panel. I wonder if there is a better way to access this so I don’t have to do so much darn trial and error.

    I have also struggled to get the backfocus correct using some small-mm separators to get it as precise as possible and my focus has improved. I’ve also done analysis on collimation of my HyperStar and (I think) it’s ok. The only avenue I know to explore is alignment of the plate. Or other?

    Appreciate any insight you (or anyone else) can provide but no reason to respond till I have posted the additional frames which may better pinpoint my issues.

    Thanks much!

    Richard (aka TheAstroTiger on Instagram).
  • BlockHeadBlockHead
    The dew shield is asking for trouble if the inner surface is shiny/reflective. These are no good for astrophotography usually. It could be one source of problems with regards to getting good flats. You might consider using black flocking paper if you have not already done so.
    -the Blockhead
  • RichardM
    Thanks Adam, 

    Re: Due Shield: It's a Celestron flexible with dark interior.  Would that be a problem?  How do you take flats without a dew shield if you are using a HyperStar?  

    Re: Flocking paper  I'll try it!  

    As I promised above I have now loaded all the work files to the link above if you could take a look.  I did not load every single of the 120 images of the lights.  I took samples from each category: calibrated, cozmetized, debayered, registered.  Also included are the flats, dark flats, and darks.  I did just notice that I used 3 sec dark flats with the 1.7 sec flats.  I do wonder if that is the source of my problem.  

    Thanks in Advance

    Richard 

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