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Another dip in the Lagoon: How warm is warm enough?

DSLR Imaging Astrophotography
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#1 BQ Octantis

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Posted 19 June 2021 - 11:48 PM

It's Milky Way season over the Red Centre, but the bloody clouds haven't relented at all this year. So I've settled for reprocessing old data. Thanks to someone's posting of the Hourglass in M8, I went all the way back to one of my first DSO captures from the outback. I didn't know much in those days—30 sec subs at 750mm unguided (crikey!), hardly any integration time (a paltry 20 minutes), and minimal calibration (if any). Armed with my newfound knowledge of using exiftool to get sensor temperatures, I even set about making some temperature-matched darks yesterday. The sensor temperature from the lights was right at 20˚C; my darks followed an asymptotic path from the 15˚C ambient to around 21-23˚C.

 

The results were quite reasonable:

 

(Click for full size @ 40% scale.)

gallery_273658_12412_342096.jpg

Capture details

 

But a look at the temperature plots showed there is still room for better darks temperature matching:

 

gallery_273658_12412_37825.png

 

My goal up to this point has been ±5˚C ambient temperature matching, but this sensor temperature is a new rabbit hole for me. What do you typically aim for when you match your darks? And do you cull the first set of darks before the camera temperature settles?

 

Just wondering…

 

BQ


Edited by BQ Octantis, 20 June 2021 - 02:04 AM.

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#2 galacticinsomnia

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Posted 20 June 2021 - 02:22 AM

It's Milky Way season over the Red Centre, but the bloody clouds haven't relented at all this year. So I've settled for reprocessing old data. Thanks to someone's posting of the Hourglass in M8, I went all the way back to one of my first DSO captures from the outback. I didn't know much in those days—30 sec subs at 750mm unguided (crikey!), hardly any integration time (a paltry 20 minutes), and minimal calibration (if any). Armed with my newfound knowledge of using exiftool to get sensor temperatures, I even set about making some temperature-matched darks yesterday. The sensor temperature from the lights was right at 20˚C; my darks followed an asymptotic path from the 15˚C ambient to around 21-23˚C.

 

The results were quite reasonable:

 

(Click for full size @ 40% scale.)

gallery_273658_12412_342096.jpg

Capture details

 

But a look at the temperature plots showed there is still room for better darks temperature matching:

 

gallery_273658_12412_37825.png

 

My goal up to this point has been ±5˚C ambient temperature matching, but this sensor temperature is a new rabbit hole for me. What do you typically aim for when you match your darks? And do you cull the first set of darks before the camera temperature settles?

 

Just wondering…

 

BQ

Darks?  What darks ;) :p

You image looks great.

I'm doing my best to try an avoid darks, flats, and bias because I just don't want spend 2/3rds of the expected lifespan of my sensor/shutter taking calibration frames.  Searching for alternative solutions, but until I find them I keep a bare minimum catalog of darks flats and bias that I will use in pinch, but usually I'm doing okay with the exception of gradients, but most software has ways to deal with it.

I do have some stacks of Lagoon if you would like. 

Clear Skies !!



#3 BQ Octantis

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Posted 20 June 2021 - 02:49 AM

Oh, I don't take many calibration frames. Certainly not 2/3 of the captures! RawTherapee uses one (1) flat and no flat_darks. But this was my first time trying to match the temperatures between the darks and the lights. I find darks do make a difference in the detail I'm able to pull out of my images. Sure, dithering and sigma-reject stacking gets rid of hot pixel noise and small-structure fixed pattern noise. But since my 600D isn't astro-modded, separating the meager Ha flux from the thermal noise is the largest benefit—especially when it's over 30˚C out! But I'd rather stab myself in the eye than solve the vignette-light pollution puzzle every time I process—and I've used the same flat for over a year!

 

Sorry, but I'll have to pass on the Lagoon data…I have many f/2.8 and f/3.8 hours' worth through the 200mm from last season. Just not much through the C5/750.

 

BQ


Edited by BQ Octantis, 20 June 2021 - 03:47 AM.

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#4 hobbyknipser

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Posted 20 June 2021 - 07:52 AM

Hi, BQ,

 

I never took darks for my DSLR, always only flats. Some cracks in our german forum said, that they didn't see a difference after postprocessing.

What would happen, if you use the photometric color calibration... Would only the stars be corrected? I think so...

Do you like the bluish look of the nebula oder would a color balance be a good idea for you? laugh.gif  I hope, you are not angry now...blush.gif

 

best wishes

Andreas


Edited by hobbyknipser, 20 June 2021 - 09:17 AM.


#5 BQ Octantis

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Posted 20 June 2021 - 06:50 PM

Thanks Andreas. But why would I possibly be angry? I am quite happy with the result. I've already done several renditions of this target, including with G2V color balance. But if colorimetry is your thing, with an unmodded DSLR the result is a drab red with a very cyan core:

 

(Click for full size @ 40% scale.)

gallery_273658_12412_150302.jpg

 

But I prefer the more bluish tone. It makes me glücklich.

 

BQ


Edited by BQ Octantis, 20 June 2021 - 06:50 PM.


#6 Tim J Fowler

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Posted 20 June 2021 - 06:55 PM

Very well done, BQ! The fact that I use the same camera always makes me take notice when you post something, and this one does not disappoint!

#7 BQ Octantis

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Posted 20 June 2021 - 07:08 PM

Thanks Tim! The 600D/T3i makes for an outstanding general OSC astrocam. It obviously has its limits; I've probably pushed them more than most. The most serious shortcoming in my stock version is the low Ha; have you had yours modded?

 

BQ




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