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Stacking Question

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#1 dallen24

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Posted 22 October 2019 - 08:58 PM

Hi.  I'm still a stacking newbie, hoping someone here could help.

 

Been having a ball stacking this summer, see http://www.stargazin...llen/photos.htm .  Running my 24" scope with a Tom O. EQ platform, Canon 450D, ISO 1600.  I can typically get 35 to 40 45 second shots on a single run of the platform.  I've been using Deep Star Stacker, just running with the recommended options.  Then I pull the RGB bells together to create a half-way decent image.  I seem to have better luck stacking jpeg than raw images.  Taking dark frames allows me more images in a run, but my bed sheet flats don't seem to make a difference.

 

Tom O. suggested I look at https://www.cloudyni...d-1s-subs-lrgb/ .  I just skimmed this thread, but it got me thinking.  Is it possible to try a set of 5 second or even 1 second images?  On my runs this summer I did 45 second images with a 5 second gap between images, for shutter shake and cool down.  Could I do 5 or even 1 second shots with no time between shots?  Is that even possible?



#2 D_talley

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Posted 22 October 2019 - 09:01 PM

You can't stack Jpeg images. They are compressed and stacking does not work with compressed files.  Could be why your flats don't work.



#3 dallen24

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Posted 22 October 2019 - 09:45 PM

You can't stack Jpeg images. They are compressed and stacking does not work with compressed files.  Could be why your flats don't work.

Well, my 450D is set to take both large jpeg and raw.  I've been using DSS to stack the jpegs.  A fellow club member uses DSS to stack my raw images, but then he uses his cloud copy of Photoshop to bring out details and colors.  I haven't figured out how to pull anything out of the raw stacked image with just my copy of PS elements.


Edited by dallen24, 22 October 2019 - 09:46 PM.


#4 zxx

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Posted 22 October 2019 - 10:04 PM

45s exposures, that's awesome, best I could do was 5s with my 12" Dob on my homemade EQ platform,  Nice images BTW....


Edited by zxx, 23 October 2019 - 11:10 AM.


#5 StarBurger  Happy Birthday!

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Posted 22 October 2019 - 10:06 PM

Well yes you can do 5-1 sec shots with no interval but why would you want to?

Shutter calm down and temperature is rarely an issue in this situation.

Also how does taking dark images in a run allow you more frames? Taking darks just gobbles up more time best spent on capturing more light frames.

Darks are more economically done with the camera/scope combo capped off at any time at a similar temperature to the light images.

I may be misunderstanding  something here with your equipment and method but the normal route is to take light exposures as long as the scope setup allows without trailing and factoring in sky brightness/LP etc.

1000 x 1 sec exposures will definitely NOT equal 1 X 1000 sec exposure when it comes to noise SNR etc. 

We can start to see the benefits with say 10 sec exposures when the sensor has had some good number of photons to fill up the photo sites but not 1 sec.

Signal to noise could be 1:1 .

I see you have a 24 inch scope (what f ratio?) so my opinions may be off the mark.

As for RAW vs jpeg I have tried it myself and there is no way that jpg excels over RAW processing.

It may look good at first blush but jpg in-camera has performed a process that is fine for high light level day time imaging but corrupts absolutely for astro purposes.

Apologies if I ever sounded dictatorial, that is not my intention and as I said, I may not have understood your methods and practice.



#6 dallen24

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Posted 23 October 2019 - 07:10 AM

My scope is a 24" f/4.5 truss tube dob on a Tom O. EQ platform.

 

In skimming that thread, https://www.cloudyni...d-1s-subs-lrgb/ , I get the impression that keeping the individual exposure times short reduces noise. It'd be interesting to try a 5 second run and compare it to my 45 second runs.

 

Yes, raw is better than jpeg, I have both.  I've been able to stack jpeg, just need to figure out how to stack and process the raw images.  Again, I don't have a full copy of Photoshop, just elements.



#7 klaussius

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Posted 23 October 2019 - 07:30 AM

9x5s exposures will give you less dark current than 1x45s, but 3x the read noise.

The math gets a bit confusing at times, but there's a tradeoff there between dark current, that grows linearly with exposure time, and read noise, that grows as the square root of the number of subs.

That means there's a sweet spot that depends a lot on your sensor characteristics. That usually lies well above 45s, around 5m in fact.

If your sensor has high read noise, like most canon sensors, longer still. If you can manage consistently low sensor temperatures (say with cooling) even koger still, since dark current depends strongly on temperature and cooling reduces it enormously.

In any case 5s is far from the sweet spot with a dslr.

#8 Tapio

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Posted 23 October 2019 - 07:44 AM

I believe nearly all graphics software has the capability to stretch astro images - even Elements.

Then there's Gimp for free and Affinity photo for $50 etc.



#9 View2

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Posted 23 October 2019 - 11:43 AM

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