Circle of Confusion Details

Circle of Confusion, the Airy Disk and Diffraction (Podcast 594)

Today I'm going to explain what causes diffraction as we stop down the aperture in our lenses past a certain point, and how this may affect our photographs. I've been working on an update to our iOS app Photographer's Friend so that you'll be able to do two new things....

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Martin Bailey
Martin Bailey is a nature and wildlife photographer and educator based in Tokyo. He's a pioneering Podcaster and blogger, and an X-Rite Coloratti member.
  • Eric Bier
    Posted at 06:38h, 30 October Reply

    Hi Martin

    The 12 photos showing diffraction appear to be mislabeled. The photo labeled f/40 appears to be the f/11 shot, so it seems that the labels are reversed.

    Thank you for this excellent podcast!

    • Martin Bailey
      Posted at 16:08h, 10 November Reply

      Hi Eric,

      Tell me, why do you think that? I just checked, and the labels look fine to me.


      • Eric Bier
        Posted at 06:23h, 11 November Reply

        You are correct. I mistook the diffraction in the f/40 shot for a lack of dof. I see it now.

        Thank you for helping me to take another look and end my confusion!

        Keep up these great articles!

        • Martin Bailey
          Posted at 13:49h, 12 November Reply

          Ahh, that’s good. Thanks for letting me know Eric.

  • David Ramsey
    Posted at 02:37h, 06 May Reply

    Martin – I just caught up with this podcast. This is terrific, particularly for those of us into the geekiness side. When the app first came out, I knew there was a debate as to the appropriate CoC, and this podcast explains it all. I’ve just received a new Nikon D850, so I’ll try approach recommended for diffraction and will let you know how it turns out. Thanks for your work and efforts on this. Very useful.

    • Martin Bailey
      Posted at 11:55h, 07 May Reply

      I’m pleased you found this useful Dave!

      I recently heard from someone with a camera that shows the depth-of-field, and it looks like the manufacturer is using very similar algorythms, as the numbers were almost identical to my Pixel Peeper mode, so that good to know.

      The Diffraction Warning is currently set to be somewhat harsh. It may be accurate for someone using average lenses, but all of my Canon L lenses work much better in my tests. I can probably build in a setting to allow people to adjust the warning levels based on their own tests if that would be useful.

      Do let me know how you get on with your tests and I’ll see what can be done.


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