The Iranian photographer Alireza Rostami also wanted to find an answer to this question, which is why he disassembled an old Zenit Zenitar-M 2S 50mm F/2 and reversed the third element whenn putting it back together. The shortest description for the resulting effect is „soap bubble bokeh“ – a type of bokeh, whose circles look like soap bubbles.
For those of you, who are now confused: this is yet another case of turning a „bug“ into a „feature“. Usually designers are trying to construct a lens in such a way, that it produces round and homogenous bokeh circles. After all, the background should be unobtrusive instead of attracting the viewer’s attention. Bokeh circles with a strong contour or even worse concentric circles (so called onion rings) are considered to be ugly. Some photographers, however, love the effect and are prepared to spend a lot of money on lenses which produce this type of bokeh. Here are a couple of photos which Rostami shot with his modified Zenitar-M.
Should you be interested to find out how Rostami modified his lens, you can do so in the following video: