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Originally Posted by GrampianStars
what the hell is this "air-pocket size"
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It has to do with a description of turbulence based on the assumption that the velocity and pressure gradients over distances less than the air pocket size are negligible. In other words, if you were to look at the air within an air-pocket sized region of the atmosphere it would not look turbulent: it would appear to be still or in uniform motion. I personally find this picture questionable, because classical turbulence is by its very nature scale independent (fractal, like my avatar
) until you go right down to the regime of discrete clumps of matter in the forms of atoms and molecules.
IMO a smaller aperture refractor can give the impression of being less affected by seeing because:
- magnifications one uses tend to be less with a refractor because of the shorter focal length of the scope
- limited angular resolution of the refractor does not allow one to resolve the bad seeing in any detail, i.e., the steady diffraction smearing of the image from the small aperture is worse than the unsteady smearing from bad seeing.
But the more I read about other people's experiences, the more I want to grab me a good 4-5" refractor and spend some time seeing how it really works with my own eyes.
I know that the ED80 was no match for my 8" Dob when the latter was properly cooled and collimated. The views did look "sharper" at low magnification in the ED80, but that was just the higher contrast due to no obstructed aperture and the darker background skies due to smaller aperture tricking my brains. When it came to making out fine detail, the Dob always won. But 80mm against 200mm is a very unfair comparison.