Editing a blend of multiple exposures

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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thewormofautumn
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Joined: Sun Nov 15, 2020 9:56 am

Editing a blend of multiple exposures

Post by thewormofautumn »

Hi all

Quick one, hopefully.

What causes artefacts like this?
Image
This is an amalgam of two sessions on Vela stacked in DSS

The first was done with 300 second subs with the L-Extreme
The second was done with 360 second subs no filter (with and without moonlight)

I took the second to get some star colour and I'm happy I can see star colour, but wondering what the big circle is. Is this just sub exposure difference? if so, any way to normalise the two?
I'm not very good with the Wipe tool btw, so maybe there's something I'm missing at that step.

Link to the saved FITS file if anyone wants to see it:

https://1drv.ms/u/s!Ak9Pmua24KTPk4x7skM ... Q?e=P3FsBl

Thanks :)
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admin
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Re: Editing a blend of multiple exposures

Post by admin »

Eek! :shock:

That looks like a flats issue to me. Try stacking without your flats and see if the problem goes away.
Ivo Jager
StarTools creator and astronomy enthusiast
Burly
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Re: Editing a blend of multiple exposures

Post by Burly »

Just a note on that issue I’ve been having issues with flats a bit like yours but inverted to yours so clear in the middle of image cloudy on the outside , finally last night I seem to have cracked the issue , I dither so take flats and bias and use bias as darks, but after experimenting what fixed it was using Astap to stack ,load bias in dark flats tab and load flats in flats tab , then analyse , Astap will create a master flat from both files , now load lights and put bias in darks tab (may work with darks in darks tab I don’t usually take darks as I dither) now analyse lights and darks then stack , doing this finally left me with an image once auto dev and wiped looked like it should I need to let Ivo look at the final stacked image but I’m 99% there in solving my issue with flats I hope .

Dave .
thewormofautumn
Posts: 22
Joined: Sun Nov 15, 2020 9:56 am

Re: Editing a blend of multiple exposures

Post by thewormofautumn »

hmmm... you're right, Ivo. I tested it without flats and besides being a noisy mess (just lights) after stretching, there was no issue like above.

So I had a look at my flats in ASTAP... and saw this for a batch of 40 I took on night 1.
Image
Wow. Okay, will chat with the NINA folks to see what I did wrong there. That's awful.
Thanks for your help.
thewormofautumn
Posts: 22
Joined: Sun Nov 15, 2020 9:56 am

Re: Editing a blend of multiple exposures

Post by thewormofautumn »

Burly wrote: Mon Apr 05, 2021 7:30 am Just a note on that issue I’ve been having issues with flats a bit like yours but inverted to yours so clear in the middle of image cloudy on the outside , finally last night I seem to have cracked the issue , I dither so take flats and bias and use bias as darks, but after experimenting what fixed it was using Astap to stack ,load bias in dark flats tab and load flats in flats tab , then analyse , Astap will create a master flat from both files , now load lights and put bias in darks tab (may work with darks in darks tab I don’t usually take darks as I dither) now analyse lights and darks then stack , doing this finally left me with an image once auto dev and wiped looked like it should I need to let Ivo look at the final stacked image but I’m 99% there in solving my issue with flats I hope .

Dave .
Thanks Dave. There's a bit to unpack here.

- I dither, as well.. usually every 3rd image. Does dithering remove the need for darks?
- I still take darks and use them as darks (in DSS). I basically take darks, flats and flat darks for my calibration and load them as such in DSS.
thewormofautumn
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Re: Editing a blend of multiple exposures

Post by thewormofautumn »

I'm told it's dew...

ha... time to turn on the 2600MC's dew heater!! It's there for a reason..
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Re: Editing a blend of multiple exposures

Post by admin »

thewormofautumn wrote: Mon Apr 05, 2021 8:59 am I'm told it's dew...

ha... time to turn on the 2600MC's dew heater!! It's there for a reason..
Awesome to hear you got it sorted and thanks for sharing the solution. I wouldn't have thought of that - it's so perfectly circular. :D
Ivo Jager
StarTools creator and astronomy enthusiast
thewormofautumn
Posts: 22
Joined: Sun Nov 15, 2020 9:56 am

Re: Editing a blend of multiple exposures

Post by thewormofautumn »

well that's what I was told, anyway :)

I have taken flats since, and haven't noticed anything but I'll definitely be inspecting them every time I take them for the next few sessions.

Anyway, I have since abandoned this project. I just can't get rid of weird light gradients in the image even when I stack only lights and flats and nothing else.
Will be starting again with fresh data hopefully this weekend.
Burly
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Re: Editing a blend of multiple exposures

Post by Burly »

Flat darks and bias are basically the same use one or the other but not both , may be worth trying using bias instead of dark flats just in case that causing an issue , I started using Astap for stacking and that lets you calibrate your flats and bias separately unlike dss leaving you with a master flat and less settings to tweak than dss ,Astap settings on Startools website if your interested .
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