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Thread: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

  1. #1
    David J. Heinrich
    Join Date
    Oct 2008
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    575

    Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    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.

  2. #2

    Join Date
    May 2002
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    1,031

    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    Is the "Robin" photo done with your modded lens or with a "real" Petzval? If that's your lens, you've certainly come up with a great idea!

    EDIT: I reread and I guess that's a Petzval. Your color shots still rock.

    I assume your mask goes behind the lens? I.E., between the rear element and the film? Do you have the mask in contact with the element or spaced away from it, and if so what happens when you vary the spacing?

    Thanks for sharing.

  3. #3

    Join Date
    Dec 2001
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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    The image you posted isn't nauseating, so doesn't have real swirlies. And I don't see the effects of mechanical vignetting either.

    Have you considered using retouching to get the effect you want? Or painting, instead of photography?

    I have a 100/6.3 Neupolar that is a reversed tessar (pair of singlets behind the diaphgragm) that's relatively long and whose elements are in a relatively narrow tube. In shots taken at distance (yes, I practice lens abuse too, the Neupolar is macro only) the result is pronounced mechanical vignetting off-axis; it doesn't have the coverage it should. No swirlies towards the edges of the area it illuminates.

    dh003i, I think you've let wishful thinking take control.

  4. #4

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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    Quote Originally Posted by Dan Fromm View Post
    ...
    dh003i, I think you've let wishful thinking take control.
    Not only, but this "invention" is also in disagreement with the basic optics rules.
    Oh, the level of this forum...

  5. #5
    David J. Heinrich
    Join Date
    Oct 2008
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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    Quote Originally Posted by Alan Davenport View Post
    Is the "Robin" photo done with your modded lens or with a "real" Petzval? If that's your lens, you've certainly come up with a great idea!

    EDIT: I reread and I guess that's a Petzval. Your color shots still rock.

    I assume your mask goes behind the lens? I.E., between the rear element and the film? Do you have the mask in contact with the element or spaced away from it, and if so what happens when you vary the spacing?

    Thanks for sharing.
    Yes, the mask is behind the lens, to create the slightly swirling bokeh. (for the heart-shaped bokeh ones, that mask was in front of the lens).

    The mask is in contact with the element, which is why I'm doing this on a cheap 50/1.4 lens (Rokkor 50/1.4 is $30); but it is just black origami paper, and is just flat with the rear element, so I don't think it damaged it anyways. When I perfect this, I will use a piece of black micro-fiber suitable for cleaning lenses to make contact with the rear element.

    I haven't tried spacing it from the rear element, but I presume that would be just the same as making the mask smaller. I'll have to try with a piece of black velvet cloth, layering it, to see if that has a different effect than just making he "hole" smaller.

    I should also play around with this on my large-format 135/3.5. It will be much easier there, as the rear element has its own protrusion, and doesn't need to screw into anything.

    So yea, I want to play around and see what will cause the swirliness to increase. My only suspicion, which must be correct, is simply that a larger rear obstruction would cause more swirliness. After all, his is a 35mm-format lens being used on a 4/3rds body; so half of the image circle isn't used.

  6. #6

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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    Quote Originally Posted by dh003i View Post
    Hi all,

    ...
    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:

    ...
    Good grief!

  7. #7

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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    Have you tried multiple holes in your mask?

  8. #8

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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    A bit like a reversed Imagon ????

    Peter

  9. #9
    David J. Heinrich
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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    Quote Originally Posted by GPS View Post
    Not only, but this "invention" is also in disagreement with the basic optics rules.
    Oh, the level of this forum...
    Well, actually, this "invention" (I'd call it a hack) isn't in disagreement with "basic optics rules". Maybe the claim that it is producing a swirly bokeh is in disagreement with "basic optics rules". I don't see the need to be insulting. In fact, I have not found a single good clear explanation of the cause of swirly bokeh, here or elsewhere. Some claim it's the lens' coma (this is verified by images, although it's a different kind of "swirliness" than Petzval lenses, more like a tear shape), others the vignetting from the rear element & the aperture being wide open, some claim it can be reproduced by attaching a cheap wide-angle adapter to the front of a lens (this may be confirmed, I've asked a user of a Yashica A, who has a swirly portrait shot,

    In fact, given this discussion of vignetting and cats eye effect at the edges of an image circle, I would indeed agree the results I see are puzzling, IF I'm not imaging things. So it could be the case that my 50/1.4 has a little bit of swirly bokeh (cats eye) naturally. It seems quite clear to me that that URL above, if you think about how the cats eye would look at the extreme peripheries, explains the extreme swirliness in the Petzval lenses. The effect starts out gradually, and in the central portion of the image, has slightly ovular cat eye shapes; then as you progress towards the edges, the cats eye gets more and more elongated. This can clearly be seen by studying this photo. It isn't he case that all of the sudden, at he edges, you have swirliness. It starts out as gradual cats eye shapes, and progresses to more and more elongated.

    I have uploaded a "negative control" of the same lens (Rokkor 50/1.4) without the mask over the rear element; you can compare (it isn't a perfect control, since it's a different tree, but same basic idea; bright specular highlights in background). I also uploaded shots with a Rokkor 58/1.2 MC (shots taken are each labeled with what lens taken with). Neither had the rear mask. It seems like maybe both have a slight cats eye effect at the peripheries. Maybe the effect seems stronger with the mask? I don't know, that doesn't make sense to me.

    I will have to try using a velvet material for several layers (to simulate a piece of black card-board extending the rear element).

  10. #10

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    Re: Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

    dh003i, you're not nearly there as Dan pointed out. I think you need to understand the peculiar optical property that yields curved out of focus circles of confusion oriented around the periphery of the image. I believe this has something to do with extreme barrel distortion in the out of focus edge COC, but I'm just guessing. Perhaps someone here has a precise optical explanation.

    Again I'm just guessing but you may make more progress by using a simple auxilliary lens element in front of or behind the normal imaging lens then refocusing to the altered focal length.

    Nate Potter, Boston MA.

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