Steve O'Meara draws it long and sharp with his 4" under Hawaiian skies, and Ronald Stoyan draws it bold and black with his 14" somewhere in the Alps. I have now tried many times and spent quite some time on it, but never seen more than a hint of a subtle dip in brightness near the center of the bulge, which might be illusory.

I used my 16" and magnifications up to 730x under dark enough skies (21.6-21.7 mag/sq arcsec by SQM-L). Generally we don't get good seeing, but I tried in decent enough conditions, when at least distorted Airy disks could be seen.

Is there any visual trick that brings it out? What conditions do you need to really see it? Apart from being transported in time and space to stand with Lord Rosse at the focus of his shiny new 72" mirror.