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DSS makes images worse?

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#1 ET_PhoneHome

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Posted 09 August 2020 - 09:32 PM

So I was playing around imaging M13 tonight.  I took 10s x 6, and fed them to DSS.  The result is less noisy (although, the original is not objectionably noisy), but the final image is blurred.  Any way to improve this? Here is a screen cap of both images cropped to 100% (single shot left, stack right).

 

Also, DSS appears to be changing the WB.  The original shots are cooler looking.

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Edited by ET_PhoneHome, 09 August 2020 - 09:32 PM.


#2 ET_PhoneHome

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Posted 09 August 2020 - 10:08 PM

Ahhh, I may have answered my own question.  My RAW files have 75 set as default sharpening, but when I import a tiff from DSS, the default sharpening is much lower.



#3 17.5Dob

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Posted 09 August 2020 - 10:23 PM

There are dozens of buried setting in DSS..The defaults are all wrong. You need to reset everything..and then learn how to process it..

Did you check each sub to make sure they were not trailed..One bad sub will destroy the batch with that few subs...You must not have sved the proper  stack, because it should have come out the same as your single sub...even darker...

This is a "throw away" shot, stacked in DSS, 16 X120" of M13, using my little 65mm OTA,

Single sub/ DSS stack..they both look the same

50209100057_4cd0c59bb0_b.jpg


A few clicks in PI processes it, and even annotates the dozens of background galaxies..

41320759015_78f82e7cdf_b.jpg




 



#4 ET_PhoneHome

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Posted 09 August 2020 - 10:36 PM

I raised the exposure on the stacked shot to see better (originally, it was as dark as the single shots).  As far as settings, I've read the recommended ones or defaults are usually pretty good.  The stars came out reasonably round, but I only took 10 second exposures.  No way could I get 120s pinpoint stars.  I guess I am not setting this mount of good enough (SkyGuider Pro), or maybe I am just expecting too much at 300mm.  I got Polaris right where it's supposed to be in the polar scope, tripod is level, camera balanced, etc.  Not sure what more I can do.

 

Anyway, getting back to the original comparison, I think the main reason the stack looked blurrier is because less sharpening was applied.  It's also less noisy, which can give the appearance of less detail.



#5 bobzeq25

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Posted 09 August 2020 - 11:32 PM

I raised the exposure on the stacked shot to see better (originally, it was as dark as the single shots).  As far as settings, I've read the recommended ones or defaults are usually pretty good.  The stars came out reasonably round, but I only took 10 second exposures.  No way could I get 120s pinpoint stars.  I guess I am not setting this mount of good enough (SkyGuider Pro), or maybe I am just expecting too much at 300mm.  I got Polaris right where it's supposed to be in the polar scope, tripod is level, camera balanced, etc.  Not sure what more I can do.

 

Anyway, getting back to the original comparison, I think the main reason the stack looked blurrier is because less sharpening was applied.  It's also less noisy, which can give the appearance of less detail.

Let me try to state clearly to you a major problem, stated in detail in #3.  Why DSS often makes images worse.

 

You're using DSS wrong.  The stack should not look like much.  Below is another example.  A proper stack from DSS, and the final image from it.  Magic.  <grin>

 

It looks dark because a proper stack from DSS is "linear" and your eyes do not see linear data well. 

 

You're stretching the stack in DSS, which is a bad idea.

 

So, save the linear stack in DSS.  When you open it in your processing program, it should look as dark as the one below.  That is correct.

 

These commands work.  Stack.  "Save stack to file".  Be sure "settings embedded but not applied" is checked.

 

Better idea.  Use Astro Pixel Processor.  It both stacks and processes, the issue never comes up.

 

Rosette(32l,f,b,d).jpg

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  • RosetteV3.2.jpg

Edited by bobzeq25, 09 August 2020 - 11:37 PM.


#6 TelescopeGreg

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Posted 10 August 2020 - 01:55 AM

Ok, so perhaps a few more details?  10 second exposure, 300mm lens; what focal ratio? What sort of camera, what ISO? How focused?

 

Regardless, M13 is a relatively small target for a 300mm optical path. You've got a bunch of stars packed into a small space, so it will be hard to resolve them. Perhaps try for a different target, such as an open cluster, nebula, or a galaxy? 


Edited by TelescopeGreg, 10 August 2020 - 01:58 AM.


#7 ET_PhoneHome

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Posted 10 August 2020 - 09:33 AM

Let me try to state clearly to you a major problem, stated in detail in #3.  Why DSS often makes images worse.

 

You're using DSS wrong.  The stack should not look like much.  Below is another example.  A proper stack from DSS, and the final image from it.  Magic.  <grin>

 

It looks dark because a proper stack from DSS is "linear" and your eyes do not see linear data well. 

 

You're stretching the stack in DSS, which is a bad idea.

 

So, save the linear stack in DSS.  When you open it in your processing program, it should look as dark as the one below.  That is correct.

 

These commands work.  Stack.  "Save stack to file".  Be sure "settings embedded but not applied" is checked.

 

Better idea.  Use Astro Pixel Processor.  It both stacks and processes, the issue never comes up.

 

attachicon.gifRosette(32l,f,b,d).jpg

It was dark when it came out of DSS.  I boosted exposure in LR to better show the stars for this post.  The image below is how it looked out of DSS.

 

This thread can be closed out.  Like I already said, the difference in sharpness I was seeing was mainly due to LR settings.  The imported tiff didn't have my usual sharpening settings applied by default, so it looked blurrier.

Attached Thumbnails

  • 4.jpg



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