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  #41  
Old 23-02-2018, 01:18 PM
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PKay (Peter)
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Hi Barry (or if any one else knows)

I don't understand 'image scale', so i have supplied a few facts about my equipment:

I have imaged with both scopes, and both seem to work fine.

Camera: 13.4 X 17.7mm sensor. 3.8um pixel size.

Scope 1:
85mm refractor.
f/6.6
FOV 82 X 108 arcmin.
Resolving power 1.36 arcsec.
Image scale 1.4 arcsec/pixel

Scope 2:
304mm reflector.
f/5
FOV 30 X 40 arcmin.
Resolving power 0.45 arcsec
Image scale 0.51 arcsec/pixel
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  #42  
Old 23-02-2018, 01:22 PM
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??
Image scale tells you how many arcsec on the sky are covered by single pixel.
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  #43  
Old 23-02-2018, 02:43 PM
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PKay (Peter)
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thanks bojan

Simple when you look at it like that.

I suppose my question should be about how image scale and camera resolution are related.

I was told that the big scope would result in oversampling??
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  #44  
Old 23-02-2018, 02:52 PM
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There is no direct relationship between image scale and camera resolution, scale is related to geometry of the optical system (focal length and physical size of the pixel
But smaller scale (less arcsec per pixel) means higher resolution, if not limited by optical quality of the telescope.
Oversampling could happen if the physical pixel size is much smaller than Airy disk... and generally it happens if aperture is small and FL is long.
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  #45  
Old 23-02-2018, 11:44 PM
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Amaranthus (Barry)
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The image scale is good for your refractor and oversampled for your reflector (though not heavily). You could try 2x2 software binning for the latter setup. But also relevant is your typical seeing at your imaging site. A general rule of thumb is to try and get the image scale at somewhere between half and a third of your average seeing. If it is way 2 arcsec then aim for an image scale in the range of 0.7 to 1 arcsec/px (roughly). Most sites are a bit worse, however, so something in the range of 0.9 to 1.5 is usually great.
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