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Test with different exposure times M31 & ASI071MC Pro

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#1 Nikguy

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Posted 11 October 2018 - 04:17 AM

All images made with a Quadruplet 100 / F:5.8 + ZWO ASI071MC Pro (Preset: HDR, Gain: 0, uncooled).

 

Post-processing: Deep-Sky-Stacker + Photoshop

 

M31_10x30_1000.jpg

 

M31_10x120_1000.jpg

 

M31_10x300_1000.jpg


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#2 happylimpet

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Posted 11 October 2018 - 04:24 AM

Nice images but they dont tell us much as theyve all been stretched differently, and of course the total exposure times are different.



#3 Nikguy

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Posted 11 October 2018 - 04:32 AM

I tried to keep the stretching process the same for every image.

 

The shots were all stretched 4 times.

 

All images taken under the same parameters like temperature, seeing, ...


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#4 evan9162

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Posted 11 October 2018 - 06:05 AM

Unrelated question - was the core blown out in individual 300s subs (or in the unprocessed 300s stack)?



#5 Nikguy

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Posted 14 October 2018 - 11:02 AM

One more attempt with 10 x 600 Secs Subs:

 

20181013_M31_10x600%2BS5.jpg


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#6 Jon Rista

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Posted 14 October 2018 - 12:18 PM

You should indeed try to normalize the total integrated exposure time for all three tests. That would mean stacking 100x30s, 25x120s, and 10x300s. 

 

There are two key driving forces for exposure. Burying the camera noise, and avoiding saturation (clipping). Clipping of some stars is pretty common and usually not an issue. Clipping object signal, though, such as the core of Andromeda, is generally something you want to avoid.

 

It looks like your 300s and 600s exposures are long enough to clip the galaxy (and even some of its satellites), so something shorter than 300s is probably best. Exactly which is best, though, would best be determined by stacking the same total amount of time with all exposure lengths, and then comparing them. (Note that just using the same stretch is usually not quite enough to truly normalize the different images, but it's a good place to start.)


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#7 Nikguy

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Posted 14 October 2018 - 12:31 PM

Jon, thanks for the tips!

 

Completely correct with the exposure series to be able to compare these also.

 

But there is another important criterion and that is the personal taste...cool.gif

 

I got into astrophotography, there were still normal films to develop. From this time I have certain ideas, how some objects must look like (because there was no other way at that time!).

 

Andromeda galaxy with a burnt out core belongs to it waytogo.gif

 

And yes, I will make another series with 100 x 30 Secs and 25 x 120.


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#8 ehunnell

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Posted 14 October 2018 - 12:32 PM

Good info. You should try some HDR processing in Pixinsight. This requires 3 sets of images at different exposures. 

 

Eddie


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#9 adamphillips

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Posted 14 October 2018 - 03:16 PM

have you looked into layer masking with short exposures for the core? certain objects really require it. you can youtube it and learn how.

 

you would probably take a bunch of say 5 second exposures and just use them for the core, so its not blown out



#10 BillHarris

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Posted 17 October 2018 - 02:21 AM

"I got into astrophotography... when there were normal films to develop. From this time I have certain ideas..." (paraphrased from Nikguy)

Tell me about it!! Not only do we have to look at exposure times differently, we have to consider the aspect of integrating multiple exposures. Our astrophotographic BIOS needs to be reset.

Not to mention many of us did B&W and now we have to think in color.

Brave new world...

#11 t-ara-fan

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Posted 18 October 2018 - 12:30 PM

 (Preset: HDR, Gain: 0, uncooled).

 

 

What do you mean by "Preset: HDR".  

 

From what I know, "Gain: 0" give the maximum well depth, but not the lowest read noise.



#12 Nikguy

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Posted 18 October 2018 - 12:45 PM

You're absolutely right!

 

Gain=0 even has the highest read-noise!

 

But if I don't have to crop, then that's no problem with the resolution of the camera (APS-C)!

 

Read-noise curve of the ASI071MC Pro Camera!

 

Rauschen.jpg


Edited by Nikguy, 18 October 2018 - 12:45 PM.



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