Quote:
Originally Posted by mental4astro
Looking at the same object, at the same time, the image in the Skywatcher has significantly LESS scatter than the GSO. Black is black, not 'fuzzy grey'.
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Alex my 2c - surface ripple causes a
very near field scatter to a star image so less ripple might give the impression of sharper star image . Whilst it is a highly technical field ,there is no optical physics around that can attribute a darker sky background to a 'smoother' mirror say between an optically rough mirror of 1/20 RMS ripple at the few mm scale and one of 1/100 RMS ripple. That is nonsense peddled by Zambuto et al . Background sky brightness is acutely sensitive to exit pupil also - it needs to be matched perfectly for a good test and of course the same eyepiece used .
I would guess the improvement in sharpness is down to a better smoother figure , and the better sky contrast is down to better quality coatings that are packed down a lot tighter for less scatter . If you don't believe that al coatings scatter light and lower sky contrast try this test . Grab a large diagonal and compare the sky contrast between looking through a binocular, then get the same view but putting a diagonal at 45 degree in the path in front of the objective. The difference will be tangible.