The Brocken Spectre Society

While on Ben Nevis some years ago I was privileged to behold a Brocken Spectre, a phenonemon created by specific environmental conditions, manifest as an oval-shaped rainbow effect, with its length longest on its vertical axis. If I remember the colours were two sets of vertically symmetrical arcs. Having no expectation of seeing one we had no photographic apparatus to hand. I would be interested to know other sightings of the same and possible descriptions and photographs.