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Why have I never done flats before?

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#1 Takashi

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Posted 14 October 2021 - 12:44 PM

For all these years I've skipped on doing flats and always thought "Nah.... not necessary". For some reason, I thought..."hmm... maybe I should give it a try?"

 

I borrowed a white t-shirt from my wife (she wondered why my telescope wanted to have a t-shirt), and off I went!

And out of curiosity I stacked images in DeepSkyStacker WITH flats and WITHOUT flats, and processed them exactly the same way (exactly the same steps/adjustments in Photoshop) just to see how big the difference was.

 

The equipment used was a WO ZS 71, 0.8x reducer, Canon 600Da, Astronomik CLS filter, AstroTrac TT320X-AG, 92 x 60s exposure, under a bortle 8 sky.

 

My conclusion?

Why have I been so ignorant and skipped flats?! I will ALWAYS take flats from now on.

Attached Thumbnails

  • With and without flats comparison.jpg

Edited by Takashi, 14 October 2021 - 01:00 PM.

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#2 KungFood

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Posted 14 October 2021 - 12:50 PM

There is a fair chunk of people in this hobby who don't use calibration frames as they should, I think it's seen by many as a complication on an already complicated endeavor. The benefit of them however, speaks for itself. Sometimes hard to see until you try it I guess. :)



#3 Takashi

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Posted 14 October 2021 - 12:57 PM

There is a fair chunk of people in this hobby who don't use calibration frames as they should, I think it's seen by many as a complication on an already complicated endeavor. The benefit of them however, speaks for itself. Sometimes hard to see until you try it I guess. smile.gif

Exactly, you hit the nail on the head! I always thought that it's complicated as it is, but truth is, that doing the extra work of doing flats actually saves me time as I don't have to do as much post-processing afterwards!

 

It's just the thing that I've known about flats for basically...forever, but always thought of them as something unnecessary. I guess it's never too late to wake up :-)


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#4 jonnybravo0311

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Posted 14 October 2021 - 01:07 PM

This needs to be pinned and required reading. Like, the very first time you ever come to this forum, you are automatically directed to read this thread and can't look at ANY other thread until you've acknowledged reading this one :p


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#5 brentknight

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Posted 14 October 2021 - 01:16 PM

OK... Why does it work?

 

I've understood that it corrects vignetting and dust spots. So why does the entire field show more contrast?



#6 KungFood

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Posted 14 October 2021 - 01:21 PM

My guess would be that while processing, since there is less need to deal with vignetting/gradients/mottling, processes like curves adjustments are able to affect the field in total, meaning a more even contrast across the full frame.



#7 brentknight

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Posted 14 October 2021 - 01:43 PM

I think I see the vignetting (especially in the upper corners), but the rest of the field should be getting full illumination (washing out because of moonglow leaking through the CLS?), but the shot with the flats is still showing more in the corners and better across the entire field.  Totally new here, but I would expect the corners to get more of the washed out effect so the darkening would be less apparent.

 

Was the effect apparent before processing?


Edited by brentknight, 14 October 2021 - 01:46 PM.


#8 lakeorion

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Posted 14 October 2021 - 02:24 PM

Proper flats allow for proper processing without having to live with grunge like this from my library...

2018-01-13 NGC 2239 Rosette copy.jpg
2016-12-22 M45 Pleiades.jpg
2017-01-14 Alnitak copy.jpg

 

An ounce of prevention is worth more than a pound of cure.  Really.  Congrats, and thanks for sharing your experience.  May it lead others to follow your example.




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