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#1 dum-dum

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Posted 28 September 2020 - 12:21 AM

Something I cannot figure out...and has been driving me insane for nearly a year...

 

I have an ASI178 and an ASI071. If I take an image of Jupiter at the same resolution for each, the ASI178 image of Jupiter visually is much bigger than the ASI071, with the same, if not better, detail. Its like its zoomed in 2-3x, but retains detail. I cannot for the life of me understand why. Why, at the same resolution, would Jupiter be much larger in one over the other?



#2 Tapio

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Posted 28 September 2020 - 12:38 AM

It's the pixel size and resolution that matters.

ASI178:
- Pixel size: 2.4 µm
- Image size: 3096 x 2080

ASI071:
- Pixel size: 4.77 µm
- Image size: 4944 x 3284

 

http://www.12dstring.me.uk/fovcalc.php



#3 Kevin Thurman

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Posted 28 September 2020 - 12:48 AM

More and less pixels means a full image on one is necessarily smaller than the other.



#4 TOMDEY

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Posted 28 September 2020 - 12:58 AM

Nearly all image presentation software normalizes the image to the pixel size (or binned, of course... if you've done that). You can, of course, scale your presentation as you see fit... but you have to tell the software to do that. Some software have hint drop-downs that will scale e.g. "Fit to Screen" (or to paper loaded in the printer) things like that.    Tom



#5 bobzeq25

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Posted 28 September 2020 - 02:06 AM

Something I cannot figure out...and has been driving me insane for nearly a year...

 

I have an ASI178 and an ASI071. If I take an image of Jupiter at the same resolution for each, the ASI178 image of Jupiter visually is much bigger than the ASI071, with the same, if not better, detail. Its like its zoomed in 2-3x, but retains detail. I cannot for the life of me understand why. Why, at the same resolution, would Jupiter be much larger in one over the other?

Because the field of view is very different.  If your FOV is large, Jupiter will appear smaller, even if the resolution stays the same.



#6 SilverLitz

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Posted 28 September 2020 - 08:58 AM

It is Image Scale.  Always focus on Field of View (FoV) and Image Scale.  Image Scale is key on small objects (relative to the sensor FoV), while FoV is key on large objects compare to the sensor.  Image Scale is a measure of resolution you can see when you crop in (aka "digital zoom") to enlarge a small part of the frame.

 

Image Scale (arcsec/px) is determined by the combination of the scope's FL and the sensor's pixel size.  You can get finer image scale (smaller number, more resolution) by a longer FL and/or smaller pixel size.

 

FoV is determined by the combination of the scope's focal length (FL) and the sensor's sensor size.  You can get larger FoV by a shorter FL and/or larger sensor size.




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