The Science of Custom Bokeh...?

Discussion in 'Digital Video' started by acearchie, Mar 13, 2011.

  1. acearchie, Mar 13, 2011
    Last edited: Mar 13, 2011

    acearchie macrumors 68040


    Jan 15, 2006
    I have done a project for university using shots where I have created my own "bokeh" (not sure what term to use but I have altered the traditional out of focus circle from a light source).

    NOT MY IMAGE but this is an example of changing the traditional out of focus circles:

    I have done this in my video but I was wondering if you could help me look at the actual science behind this effect so I can add a part to my presentation of how this effect actually works and why.

    If anyone has any information as how to refer to this effect as well it would be helpful as it is not particularly well written up online so I don't know how to refer to it.

    I made my masks not as images but as words so there were gaps between the letters almost making the "filter" act as a diffraction grating. Not too sure how to explain this in so many words though.

  2. xStep macrumors 68000

    Jan 28, 2003
    Less lost in L.A.
    Load one of your own images?
  3. acearchie thread starter macrumors 68040


    Jan 15, 2006
    My aren't images but are video and I am away from the computer. When I get back to my laptop tonight I will upload a freeze frame.
  4. chrono1081 macrumors 604


    Jan 26, 2008
    Isla Nublar
    I'm not quite sure I understand what your asking but for a scientific explanation of what bokeh is and how it works look up the physics of thin lenses. This should give you what you want. (Its been awhile since I dabbled in optics so if I'm wrong someone please correct me!)

    Also there is no special name for custom bokeh, its just bokeh. I'm guessing you are using a lensbaby with the custom aperture kit. I had a lot of fun with those when they first came out and still occasionally use them.
  5. acearchie thread starter macrumors 68040


    Jan 15, 2006
    Being a student on a low budget I made my own cardboard kit which I was able to pop under a UV filter that I attached to a Canon 85mm f1.2 which I rented from the university.

    I've uploaded an image which should hopefully demonstrate the similarity between the diffraction filter and my image.

    This image is a screenshot and therefore not an actual indication of the quality of my work! I don't think the freeze frame does the short piece justice!

    I think I need to find more information on the physics of lenses and how the aperture shape influences the shape of the bokeh as through the make shift kit I am altering the shape of the aperture.

    Attached Files:

  6. KeithPratt macrumors 6502a

    Mar 6, 2007
    I'm not in full command of the facts here so don't quote me, and don't pass it off as your own if speaking to anyone who might know something on the subject.

    On the technical side I think you need to be looking into Circle of Confusion, spherical aberration, and Fraunhofer and Fresnel diffraction.

    As for a more basic explanation... Well, you need to keep in mind that if we had a camera of infinite resolution we could keep enlarging its prints to find what we thought was in focus is actually no different from the out of focus areas. Essentially, an image is made up of the circles/hexagons/hearts that are visible in the out of focus areas — they're just increasingly small as you move towards the plane of focus. You know those paintings you made as a kid, using a potato you'd cut into a shape and dip in paint? Well a photo is like that but with a vast range of different size potatoes, from the biggest King Edward to the tiniest Jersey Royal.

    Sorry, that probably wasn't much help. But if you want to know more about potatoes, just ask.
  7. acearchie thread starter macrumors 68040


    Jan 15, 2006
    These are perfect! Now I have the search tools I need to be able to research the topic further. Previously I was a bit stuck as I knew what I wanted to find but I didn't know what terms to exactly search for!

    The circle of confusion is particularly useful and will be very helpful to my project! Thanks for your help.

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