It is fair to say there is an awful lot of nonsense talked about bubbly bokeh, so I think I’ll just add to it…
This is not some mystical preserve of Meyer Trioplan lenses, nor is it just limited to the preserve of triplet lenses, it is simply a characteristic where the lens gets the chance to reflect back in on itself halfway down the lens barrel.
Most of the time this effect gets simply blocked out by the placement of the iris mechanism, so the edge ring of reflection never gets formed. Generally most lens designers would frown on this undesirable effect, but some just thought of it as a trivial matter, as who in there right mind would want to use the lens wide open anyway.
But trioplans reputation is unfortunately a bit of hype, and they really just inhabit the no-man’s land in this category; they are not the sharpest, they are not the best made, and they don’t form the best bubbles – and oh yeh, and they are ridiculously overpriced.
My favourite solution is to use triplet (or triplet derived) slide projector lenses, These, depending on the maker, will give you bokeh to die for and in some cases better sharpness than a wide open trioplan.
In the above shot (sharpness was not the aim, light and texture was) I used a Chiyoko P-Rokkor 75mm f2.5 lens from a Minolta Mini projector. However, the key to the effect is not the lens, but highlights of the correct luminosity in the background, so foliage in the woods is always a good place to start..