Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Flats failed - can anyone save my session?

  • Please log in to reply
26 replies to this topic

#1 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 13 February 2018 - 10:00 PM

Long story short: As part of a failed attempt to clean some dust off my sensor, the glass in front of my camera's sensor got spots on it and my flats failed. I can't figure out why my flats failed, but this happens to me about 10% of the time (oddly, I'll be working on two images at the same time and in one the flats will work perfectly and the other, things will have rotated just a tad). I managed to fix the glass and my session from last night looks fine (and my flats worked anyway), but my session from the February 8 looks terrible. I tried combining the two sessions but I couldn't fix the reflections of the spots from the first session.

 

I'm wondering if someone who works with PixInsight is aware of a simple process or script for smoothing out the background so that I won't have to trash 5.5 hours of data. If no such process exists (or if it takes time), then I'd prefer trash the data rather than take up someone else's time.

 

I'm attaching a very compressed JPEG to give an idea of what happened with this image. The original stack can be downloaded here: https://drive.google...k4p-2e9DiVGdyy 

Lum_Stack_dirty_small.jpg

 



#2 Alex McConahay

Alex McConahay

    Fly Me to the Moon

  • *****
  • Posts: 6224
  • Joined: 11 Aug 2008
  • Loc: Moreno Valley, CA

Posted 13 February 2018 - 11:14 PM

Were you using batch or individual calibration?

 

In batch sometimes things flash by on the processing console and you do not see warnings about mismatched flats. 

 

Try the individual calibration processes and see what you get. 

 

Alex



#3 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 14 February 2018 - 12:18 AM

I'm using DSS to stack - I think it only has the ability to do batch calibration. 



#4 miwitte

miwitte

    Viking 1

  • *****
  • Posts: 710
  • Joined: 28 Dec 2016
  • Loc: Charlotte NC

Posted 16 February 2018 - 09:51 PM

Hey I was going to try astroflat in photoshop, but data is not there anymore



#5 anismo

anismo

    Fly Me to the Moon

  • *****
  • Posts: 5871
  • Joined: 30 Jan 2014
  • Loc: Austin, TX, USA

Posted 16 February 2018 - 10:12 PM

'Hi Chris

 

I will be able to build a synthetic flat for this and clean it up. I will ping you once I get a chance to clean it up.

 

EDIT: That drive link is no longer active


Edited by anismo, 16 February 2018 - 10:20 PM.


#6 schmeah

schmeah

    Skylab

  • *****
  • Posts: 4297
  • Joined: 26 Jul 2005
  • Loc: Morristown, NJ

Posted 16 February 2018 - 10:41 PM

Yes, I think I can salvage this as well, but in photoshop. Can’t open your link though.



#7 miwitte

miwitte

    Viking 1

  • *****
  • Posts: 710
  • Joined: 28 Dec 2016
  • Loc: Charlotte NC

Posted 17 February 2018 - 10:02 AM

would love to hear how to build a synthetic flat for just such occasions.



#8 anismo

anismo

    Fly Me to the Moon

  • *****
  • Posts: 5871
  • Joined: 30 Jan 2014
  • Loc: Austin, TX, USA

Posted 17 February 2018 - 12:54 PM

I use David Aults instructions : http://trappedphotons.com/blog/?p=756



#9 Ladyhawke

Ladyhawke

    Apollo

  • *****
  • Posts: 1456
  • Joined: 06 Jan 2014

Posted 17 February 2018 - 01:17 PM

I don't know how to do to create synthetic flats but I've been there with the same issue a couple of times and I can guarantee you, something is moving on your imaging train, no doubt. One of the times it was my Moonlite focuser, it had a TINY play, the screws got lose during the winter and as I slewed towards zenith it would move a hair, just enough to get that embossed look on my flats, so check everything on your imaging train for movement.


  • gunny01 and xiando like this

#10 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 19 February 2018 - 10:28 AM

I'm so sorry for not getting back to everyone - I went away for the weekend for a friend's 40th birthday. I have re-uploaded everything and now have two files in the folder: The one labeled '6' had different flat stacking settings with more iterations that seemed to make things slightly better (but still unusable). I'm not sure if this is going to make things worse, but most of the data is with the dirty sensor glass, but three hours of it are with the cleaned glass. I've stacked that data alone and it looks fine.

 

I don't know why the original link didn't work. The folder can be found here:

https://drive.google...AwdS9O6wMx_6N8-

 

I think Samara is right: I think the focuser itself is turning slightly. This is definitely user error - I've only taken this scope out 3 times and don't quite know yet what I'm doing. For those who haven't used this scope, there's a metal ring at the end of the focuser that, when unscrewed, lets you rotate it. I've been using it to make sure I'm 100% lined up with the crosshairs, but I can imagine that the first time I was out that I didn't lock it down all the way. I have the stock focuser on the GSO RC8 - it seemed fine to me when first using it (and loads better than one stock focuser I had on a scope I no longer have), but I've heard horror stories about this focuser on this and many other forums. I guess it's time to start saving up for a Moonlite?

 

Thanks again for everyone's responses!



#11 pyrasanth

pyrasanth

    Viking 1

  • *****
  • Posts: 767
  • Joined: 08 Jan 2016

Posted 19 February 2018 - 04:20 PM

Sometimes for inexplicable reasons my flats have failed me. On those occasions a "live" image has come to the rescue.

 

On many occasions I have left the telescope imaging all night and have done spot checks every few hours (when the opportunity has arisen) to check that the telescope is still imaging and sometimes it has clouded over. This is good & bad- your not capturing anything but you are producing in some instances  usable frames that can be used as flats. Only one of these frames with no stars, often 10 minute exposures, can be enough to flat field the successful images you took.

 

I was amazed that only one of these images (it is rare to get a full usable RGB set- The L frame works well for RGB as well) acts as a pretty decent flat in its own right- nearly as good as a full integrated set. This can be a life saver if your flats fail- so all might not be lost.


  • happylimpet likes this

#12 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2135
  • Joined: 26 Aug 2012

Posted 19 February 2018 - 09:04 PM

The new large-scale pixel reduction in PixInsight 1.8.5 should take care of those dust moles. Then it comes down to your DBE skill.  You might also want to play with the pedestal especially if you can see dust moles on the flats.


Edited by akulapanam, 19 February 2018 - 09:05 PM.


#13 anismo

anismo

    Fly Me to the Moon

  • *****
  • Posts: 5871
  • Joined: 30 Jan 2014
  • Loc: Austin, TX, USA

Posted 19 February 2018 - 09:23 PM

I cleaned it up in PI and the updated image is at: https://zerg.codelat...fft86uccn28upzk

 

synthflat.jpg



#14 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 20 February 2018 - 10:00 AM

Thank you so much, Anis! This is waaaaay better than my muddled attempts with Photoshop and clone stamping. Okay, okay, maybe I do have to give PixInsight another look... Do you still have that synthetic flat in case I want to (or rather 'can') add data?



#15 anismo

anismo

    Fly Me to the Moon

  • *****
  • Posts: 5871
  • Joined: 30 Jan 2014
  • Loc: Austin, TX, USA

Posted 20 February 2018 - 10:04 AM

I can get you the synthetic flat (I didnt save it) but you probably cant use it if you are going to add additional data because, typically, it will be different depending on your final stack, so if you do end up with more data and want a new flat, just ping me here or in facebook and I should be able to get it to you pretty quickly.



#16 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 20 February 2018 - 12:12 PM

Okay - I think I'm going to try living with this for the lum and just grab color data. The first clear night in the forecast is February 27 - even if that stays clear, the moon phase wouldn't work for lum. I'll message you if I think making a super lum with RGB data would add to this - if I end up grabbing it during the full moon, that probably means it won't be worth it. I'll experiment with what I have before messaging you. Thanks again!



#17 Mert

Mert

    Fly Me to the Moon

  • *****
  • Posts: 5097
  • Joined: 31 Aug 2005
  • Loc: Spain, Pamplona

Posted 20 February 2018 - 02:44 PM

The new large-scale pixel reduction in PixInsight 1.8.5 should take care of those dust moles. Then it comes down to your DBE skill.  You might also want to play with the pedestal especially if you can see dust moles on the flats.

I am using 1.8.5 but can't find that utility/process ( Large scale pixel reduction )

Could you point that out to me please?



#18 akulapanam

akulapanam

    Vanguard

  • *****
  • Posts: 2135
  • Joined: 26 Aug 2012

Posted 20 February 2018 - 03:32 PM


The new large-scale pixel reduction in PixInsight 1.8.5 should take care of those dust moles. Then it comes down to your DBE skill. You might also want to play with the pedestal especially if you can see dust moles on the flats.

I am using 1.8.5 but can't find that utility/process ( Large scale pixel reduction )
Could you point that out to me please?

It’s at the bottom of the imageintegration process. Details on use in this thread. https://pixinsight.c...p?topic=11067.0 I find it to be very effective.

#19 happylimpet

happylimpet

    Vanguard

  • *****
  • Posts: 2479
  • Joined: 29 Sep 2013
  • Loc: Southampton, UK

Posted 21 February 2018 - 08:52 AM

There's a really simple function in FITSWORK (free) called 'variable flat' which cures this sort of thing in a flash. You just mask out the non-background areas with a slider or with the mouse. Its superb.


  • ChrisPA likes this

#20 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 21 February 2018 - 11:20 AM

I'm going to have to check that out - I've been using Fitswork for over a year, but I usually only use it for inspecting my subs and sometimes debayering single subs when using the color cam. It seems a bit tedious for stacking, but I need to investigate some other features it has.



#21 happylimpet

happylimpet

    Vanguard

  • *****
  • Posts: 2479
  • Joined: 29 Sep 2013
  • Loc: Southampton, UK

Posted 21 February 2018 - 11:23 AM

I'm going to have to check that out - I've been using Fitswork for over a year, but I usually only use it for inspecting my subs and sometimes debayering single subs when using the color cam. It seems a bit tedious for stacking, but I need to investigate some other features it has.

I use it all the time. Its a superb bit of software.



#22 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 21 February 2018 - 11:45 AM

@happylimpet: This is great - I've been playing around with this for the past few minutes and while It's not as smooth as what Anis put together, I'm definitely getting somewhere. With the radius set at 25, it meshes with the background pretty well, but doesn't take care of all of the spots 100%. With the radius set at 20, it's pretty much there, but there's too much of an abrupt jump between the masked and unmasked parts, but if I layer the two in Photoshop, mask, Gaussian blur, etc. it should work out fine. Thanks so much for letting me know about this - this is a really easy routine!

 

Anything else about Fitswork I should know about? I feel stupid for never having explored this program to its full extent before - perhaps I should have downloaded this in English instead of German? If anyone's curious, this process is found at Bearbeiten > Ebnen > Hintergrund ebnen variabel.


  • happylimpet likes this

#23 Mert

Mert

    Fly Me to the Moon

  • *****
  • Posts: 5097
  • Joined: 31 Aug 2005
  • Loc: Spain, Pamplona

Posted 21 February 2018 - 03:42 PM

 

 

The new large-scale pixel reduction in PixInsight 1.8.5 should take care of those dust moles. Then it comes down to your DBE skill. You might also want to play with the pedestal especially if you can see dust moles on the flats.

I am using 1.8.5 but can't find that utility/process ( Large scale pixel reduction )
Could you point that out to me please?

It’s at the bottom of the imageintegration process. Details on use in this thread. https://pixinsight.c...p?topic=11067.0 I find it to be very effective.

 

Thanks Akulapanam, I did completely oversee this option ( well hidden for sure blush.gif )



#24 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 04 May 2018 - 12:45 PM

I just wanted to share my final image with everyone who helped me out here, particularly "happylimpet" as Fitswork is what I ultimately used to fix this one. Full resolution is available here: https://www.astrobin.com/338207/

Attached Thumbnails

  • ForCN_Shrunk.jpg

  • tcchittyjr, happylimpet, gunny01 and 2 others like this

#25 ChrisPA

ChrisPA

    Explorer 1

  • -----
  • topic starter
  • Posts: 84
  • Joined: 14 Apr 2016

Posted 07 May 2018 - 02:43 PM

FYI: After trying to process another image and failing again (even when I took flats before and after an imaging session), I decided to take everything apart and clean it again to see if I could eliminate as much dust as possible to keep this from happening again. In doing so, I finally found the underlying cause. Samara was right - something was spinning, namely: My filters! I use 1.25" filters screwed into the filter wheel. They were all loose just rolling back and forth in the screw-in threads of the filter wheel.

 

I took about 800 mostly 180 second of the Draco Triplet and I think it's toast, as I was having terrible issues getting the central galaxy's halo to appear and there's a chunk of dust right in the middle of it. I tried my Fitswork process and it didn't really work. Oh well - my next image should be fine at least! Thanks again for everyone's help!




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics