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Darrellc

Need help with DSS scoring

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  I am a rank beginner in astrophotograhy and I am looking for some help with in understanding what is the difference between these two images and why one scores so much higher than the other one in dss.  The equipment involved is a skyguider pro, Nikon D5300, and a Nikon 24-70 2.8 lens.  These were shot at 70mm and f2.8.  ISO was 1600 and exposure time was 1’ 36”.   The first image had a much higher score than the second one.  To my untrained eye the second image looked much better.  When I started the shoot the moon was about half way illuminated and was directly opposite of the target.  After about an hour and a half into the shoot the moon had set.  I have been pretty good at figuring out mistakes I’ve made with other shoots but this one has me totally baffled.  Any help would be greatly appreciated.

DSC_0001.jpg

DSC_0130.jpg

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DSS scores images on a number of factors but I have no idea what the weighting factors are for each (a question for the DSS forum).  The upper image appears to have round stars across the whole image whereas the lower image seems to have elongated stars in the corners. What does DSS report for the the FWHM value for each image?

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From the FAQ

What is the score, and what is its meaning?
The score is a measure of the picture quality.
To put it simply, the higher the score, the more round and not too big stars were found.

<edit didn't read OP properly>

 

 

Edited by Kryptic

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The first image has a FWHM score of 7.03 and the second one is 8.30.  The total score for the first one was 890.  This image was taken a few nights earlier with a Nikon 85mm at f1.8 and 1’ 15” exposures.  The score on this one was 9160 and the FWHM score was 5.26.  Again my untrained eye thought the second image from above was way better than this one and yet it scored so much higher.  I forgot to mention that I used 50 darks and 20 bias files but no flats.  I assumed the stars in the corners were elongated due to vignetting.

DSC_0135.jpg

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Stars in third image:

image.png.598a51077a19015d659024d38975dcb7.png

in focus ...

Stars in first image:

image.png.ff9fc7fae64d3ea74babea184f474842.png

very out of focus

Stars in second image:

image.png.46b66b5886549a7ee03a13851e1faa36.png

even more out of focus.

In any case - you should not compare DSS score between different sets - within a set - it gives you some sense of how good frame is compared to other frames in that set.

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1 hour ago, vlaiv said:

Stars in third image:

image.png.598a51077a19015d659024d38975dcb7.png

in focus ...

Stars in first image:

image.png.ff9fc7fae64d3ea74babea184f474842.png

very out of focus

Stars in second image:

image.png.46b66b5886549a7ee03a13851e1faa36.png

even more out of focus.

In any case - you should not compare DSS score between different sets - within a set - it gives you some sense of how good frame is compared to other frames in that set.

Thanks.  I thought I had it in focus but apparently not.  
 

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On 21/11/2020 at 19:35, Darrellc said:

The first image has a FWHM score of 7.03 and the second one is 8.30.  The total score for the first one was 890.  This image was taken a few nights earlier with a Nikon 85mm at f1.8 and 1’ 15” exposures.  The score on this one was 9160 and the FWHM score was 5.26.  Again my untrained eye thought the second image from above was way better than this one and yet it scored so much higher.  I forgot to mention that I used 50 darks and 20 bias files but no flats.  I assumed the stars in the corners were elongated due to vignetting.

DSC_0135.jpg

Forget about using this lens at f1.8, to many abberations.
Stop it down and they might improve.

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9 hours ago, wxsatuser said:

Forget about using this lens at f1.8, to many abberations.
Stop it down and they might improve.

  Yeah, I was actually thinking the same thing.  I had meant to set it at 2 but forgot to do it before I started shooting.

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