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I'm used to applying Nyquist/ Shanon sampling which basically says the star image should cover at least 2-3 pixel to ensure adequate signal information.
Some of the guider set-ups don't even achieve a full pixel width on 2 -3 arcsec images.
If the image is smaller than one pixel even as it moves around within the pixel the pixel intensity is the same (??!)
Thinking about your example:
""On my 6” f6 newt ( fl 900mm ) the image scale with my new ZWOASI2600MC is 0.86 arc sec per pixel""
The pixel size is 3.76 micron and the 2 arcsec FWHM is 8.7 micron, this gives a "good" sampling of 2.3.
""My 60mm guide scope ( fl 240mm) with ZWOASI120MM-S image scale is 3.22 arc sec per pixel"
The pixel size is 3.75 micron and the 2 arcsec FWHM is 2.3 micron, this gives a "poor" sampling of 0.6.
This suggests to me that the guide star could move around by >2 arcsec and still be only within one pixel.
What happens to the imaging guiding? It doesn't seem to be <2 arcsec
Does guiding give big round stars or small round stars?
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