Questions on Custom Bokeh?

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

  1. acearchie macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #1
    I realise that double posting is sort of frowned upon in this forum however, I really didn't know which sub forum (digital photography or digital video) to put this in but since it's for a university project I was wondering whether I would be able to get the extra help.

    I am doing a presentation on some experimentation I have done on custom bokeh and I was wondering whether anyone could help me with the science behind why and how the image is created?

    I have attached a photo in the other thread I have created if people aren't quite sure on what I mean. http://forums.macrumors.com/showthread.php?t=1116007

    Thanks
     
  2. Ruahrc macrumors 65816

    Joined:
    Jun 9, 2009
    #2
    But then we'd deprive you of learning it for yourself :)

    Besides, I don't think "that's what I read on the Internet forums" would be an acceptable citation source...

    Ruahrc
     
  3. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #3
    The reason is basically the same reason that you get polygons of various numbers of edges based on the number of aperture blades (and the reason modern lenses have curved aperture blades to give circular bokeh). So any reading you do on conventional bokeh will give you the answer.
     
  4. acearchie thread starter macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #4
    I sort of stupidly realised this not so long ago! It's all my physics A-Level coming back to me.

    Attached is a screenshot and I was wondering whether anyone could help me decide whether there is an effect similar to a diffraction grating look? (Not very good with my words on this matter so I hope that makes sense!)

    Thanks
     

    Attached Files:

  5. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #5
    Maybe. But it could be down to a crappy lens. I'm pretty sure there are ways that poorly correct lenses could produce that sort of thing.
     
  6. acearchie thread starter macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #6
    I was using a canon 85mm f1.2 lens which I wouldn't really describe as crappy so I think it is more to do with something along the lines Fraunhofer and Fresnel Diffraction.
     
  7. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #7
    Lol! Most certainly not a crappy lens! In that case some for of diffraction is likely. Unfortunately my optical science is not really all that great :(
     
  8. HBOC macrumors 68020

    Joined:
    Oct 14, 2008
    Location:
    SLC
    #8
    Please forgive me for the first image. It is blurry as I was wasted when I took this (my fiance was as well, who is in this image..but I really like the photo anyways).

    It was taken w/o @ f/1.4. The DOF was shallow, allowing the background to be OOF (bokeh, japanese word for OOF background, more or less). The lens used was the FABULOUS Vivitar (also known as Rokinon, Samyang, Bower, Falcon, etc) 85mm 1.4. The second image of the tulip was taken at f/4.5 on the EF 17-40L. The bokeh is nice, but not as "crazy" as the first image, due to the aperture used, as well as focal length.

    "Bokeh" is dependent on the lens used, aperture. FL (focal length) is not as important as aperture or lens. You can get decent bokeh on a "cheap" lens (kit lens), but usually the faster the lens, the better you are going to get (f/4 or faster).

    Oh the last image was taken with a Canon 100mm Macro 2.8 @ f/2.8. That has amazing bokeh as well!
     

    Attached Files:

  9. joelypolly macrumors 6502

    Joined:
    Sep 14, 2003
    Location:
    Melbourne & Shanghai
    #9
    The same sort of principles apply when you step down your aperture but you still get the same image but darker instead of a image with only the centre visible. Same reason pin hole cameras work.

    The aperture shape determines the general shape of your bokeh. The in focus areas are where the light rays are able to converge with some accuracy on the focal plane but the out of focus areas are "scattered" and take on the shape of the aperture, round, hexagon, pentagon etc.

    Hope that makes some sense...
     
  10. acearchie thread starter macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #10
    Thanks for all the help guys.

    I had my presentation today and I got full marks so I am pretty chuffed.

    Here is the video that I made as a final piece.

    http://www.youtube.com/watch?v=hJwcreczL4A

    Thanks again.
     
  11. robbieduncan Moderator emeritus

    robbieduncan

    Joined:
    Jul 24, 2002
    Location:
    London
    #11
    Congratulations. And wow! The video is really cool. All optical? No cheating?
     
  12. acearchie thread starter macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #12
    No time for cheating! Plus is think that has to be one of the things that is so much faster to do in camera than attempting to do in post which I reckon would take a crazy amount of time!

    Thanks for the feedback!
     

Share This Page