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Arcseconds per pixel

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#1 Yourjones

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Posted 23 December 2019 - 07:35 AM

Hi

 

 

When it comes to picturing double stars with prime focus of DSLR connected to the same telescope, is it reasonable to believe that the LESS arcseconds per pixel the camera, the BETTER the "gap" between the double is seen, now that for some challenging double stars, the gap seems very narrow. Or is it totally the other way reverse in understanding the mechanism here?

 

Thanks!

 



#2 GoFish

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Posted 23 December 2019 - 07:48 AM

Fewer arcseconds per pixel = more resolution = “bigger” gap. 

 

1.0 “/px image scale would show more detail than 2.0 “/px image scale (seeing conditions aside). 


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#3 sg6

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Posted 23 December 2019 - 08:52 AM

Numbers and the ideal state say it should however what do you do if a star falls at the corner point of 4 pixels?

 

Had the image scale explained to me years ago and it was all explained as "The star falls (exactly) on this pixel". Well you cannot guarantee that occuring. Fair chance a star image will fall over 2 or more.



#4 TOMDEY

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Posted 23 December 2019 - 09:10 AM

Hi

When it comes to picturing double stars with prime focus of DSLR connected to the same telescope, is it reasonable to believe that the LESS arcseconds per pixel the camera, the BETTER the "gap" between the double is seen, now that for some challenging double stars, the gap seems very narrow. Or is it totally the other way reverse in understanding the mechanism here?

Thanks!

Yep, that's true. The computation is simple, others will probably chime in with that... so I won't steal their thunder. If you want decent visibility separation, or (especially) doing metrology of the Position Angle and separation... you would want ~over-resolution~ beyond the more common Q values recommended for general imagery. That mitigates spatial phase and non-isotropic sampling that otherwise badly degrade such measurements. Other than that... your system needs to reasonably resolve the pair... things like residual system aberrations, seeing, etc.; otherwise all bets are off.

 

[Daniel Malacara and I did a white paper on this sorta stuff a few decades ago. Couple of excerpts attached. >>>]    Tom

 

~ click on ~ >>>

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  • 58 dey malacara white paper excerpts.jpg
  • 58 dey malacara white paper 73.jpg

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#5 ssmith

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Posted 23 December 2019 - 10:55 AM

Had the image scale explained to me years ago and it was all explained as "The star falls (exactly) on this pixel". Well you cannot guarantee that occuring. Fair chance a star image will fall over 2 or more.


How the star image is distributed on the pixel grid is only of concern if you are doing measurements. That is why you should always do measurements on multiple images and average the values which will help correct for these potential centroiding and sampling anomalies.

Edited by ssmith, 23 December 2019 - 11:17 AM.

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