Hi all,
Swirly Bokeh Modification of a Lens: Pictures
Thanks to various posts by people in these forums and elsewhere online, I think I've figured out a way to get swirly bokeh patterns on any lens. It is just caused by physical vignetting of the rear element; this causes oblique light bokeh patterns (closer to the edge) to have a cats eye effect:
To get the swirly effect seen in the shots below, I used a Minolta Rokkor-X 50/1.4 with my Olympus E-3. The Rokkor is connected to the E-3 via an adapter. (this is important, as the adapter puts a little space between the rear element and the E-3 body, so I can tape on the hole.
I cut out a circle, and cut a hole in it, and taped this to my rear element. The hole in the circle is smaller than the rear element. Hence, there is physical vignetting on the rear element of the lens. This seems to "obstruct" light entering obliquely, causing a circular cats eye bokeh pattern (swirly bokeh).
It was of course a sloppy circle, so the bokeh patterns, even in the middle, are imperfect circles. And it didn't produce a lot of swirl, so maybe I need to make a smaller circle to produce more vignetting and swirl effect. I want something like the Petzval lenses -- see here http://tinyurl.com/petzval -- whereas if you look at my shots, the swirliness is mild compared to the Petzval (the Petzval has that level of swirl near the middle of the image, and much more at he edge).
I think the Petzvals produce this effect because of the nature of the barrel lens, which obstructs light when you require a wide coverage.
PS: Also, by putting a cut out in front of the lens, as I do to create these heart-shaped bokeh patterns, you can change the shape of the bokeh pattern (although not in a way that creates swirliness). If you leave the aperture diaphram wide open, and place a cutout shape in front of the lens, that effectively acts as the diaphram (as long as it is within the "effective" aperture in front of the lens). This opens up the possibility for creating perfectly circular bokeh, as well as any pattern you want.
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