Interesting discussion. From theory, I would not have expected to see this one at all with my SW 180 Mak, but I gave it a try last night when the clouds parted enough. Seeing was about 4/5 near the zenith, much poorer further down.
There was a clear bright spot seen on the inside of the diffraction ring at x340 (which was also visible at x225 but more difficult to estimate the position). There were no other bright spots around the ring or any other visible artefacts. I estimated PA to be about 350 degrees from drift direction, which seems about right. (I also swung across to Zeta Bootis afterwards, which was elongated to a clear peanut).
once again, what you see is not reliably predicted from theory and catalog data, especially the four significant digits type of calculation ... a point i've made many times in this forum.
sidgwick's caution about "theory" is frequently forgotten:
"At normally encountered ƒ/ratios (say, ƒ/5 to ƒ/20) no intensity gradient across the disc is perceptible, the border between the disc and the first minimum appears nearly sharp, and the rings are brighter than theory would indicate, the first ring being not much fainter than the disc itself. ... The visible extent of the disc, like the number of rings visible, varies for a given instrument with the brightness of the source, although the discs are in fact the same size, irrespective of brightness."
or vasco ronchi:
Vasco Ronchi (1961) noted the important difference between the ethereal image or unseen physical characteristics of the actual star, the calculated image or theoretical representation of this image in an optical instrument, and the detected image that actually appears to the astronomer's eye. Remarkably, optical theory in the form of the calculated image, a "mere mathematical construction," does not describe the detailed visual appearance of a stellar detected image.
i think it was konstantin who reported rodlike appearance in matched binaries below the resolution threshold, which some people ruled "impossible" or "unbelievable" based on optical calculations. yet van den bos made the very acute judgment, based on unimpeachable experience, that visual perception is not simply an optical task:
The born double star observer is probably, like the artist, the type with the highly developed nervous system, with the lightning-like reaction; to speak in present day terms [this is in 1944]: the born fighter pilot. It is not enough that the eye forms a faithful image of very fine structure on the retina; the optical nerve and the brain must be able to follow instantly the perceptual changes of the star image and to interpret them correctly. It seems that to a person of slower nervous reaction, no matter how keen his eye may be, the telescopic image of a difficult double star becomes just a patch of light, in no way differing from that of a single star. Even among the born double star observers there appear to be significant differences however. For instance, having dealt with a great mass of observational material, I am left with the impression that, while Burnham was on the one hand not quite so good as Aitken or Hussey in discovering pairs far below the separating power of the instrument, but with components of nearly the same brightness, he was unrivaled when it came to making out a faint companion close to a bright primary — undoubtedly the most difficult type of double star to deal with.
note that he clearly equates a significant part of the observational task as dependent on "brain stuff" beyond the retina, and the fact that "the separating power" doesn't limit detection or discovery.
optical performance is optical, and visual perceptions are visual. you can't equate one with the other. i'm continually surprised that people cheerfully take optics as the rule of law for perception, then get out their pocket calculators and dictate visual appearance to the milliarcsecond of separation and the ten thousandth part of brightness.
some posts above describe clever methods to troubleshoot and overcome observing difficulties. a great part of double star observing at the limit involves persistence, patience, good conditions, and trial and error methods to eliminate obstacles or find the "just so" magnification necessary for the challenge.
Edited by drollere, 06 June 2016 - 12:14 PM.