Edward posted:

Isn't Dawes an empirical limit, a rough description of what we are typically
able/not able to resolve? Seems to be quite a few who claim to have
surpassed its "limits".

Yes, but the duplicity of close doubles can be detected at separations which
are a little less than that listed by Dawes. In fact, an elongation of the
star image of a close double star is observable at a separation which is
noticably less than Dawes. I prefer to use the Sparrow criteria which has the
brightness level constant along a line running from the center of one
diffraction disk to the center of the adjacent one (in English units, the
Sparrow limit is about r = 4.47/D, where D is the aperture in inches and r is
the separation in arc seconds). At that separation, the "notching" is still
visible, but perhaps not quite as prominent as at the Dawes level (4.56/D).
Clear skies to you.
--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

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