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What is this aberration ?

Discussion in 'Creative Corner' started by blue, Aug 25, 2010.

  1. blue

    blue Mu-43 Veteran

    281
    Jun 1, 2010
    UK
    I don't know the correct label for this halo effect (round the out of focus red petals) - but what causes it and how is it avoided ?

    I have several with this problem but am showing these taken at f2.8 and f11 - ie stopping down has not really helped

    [​IMG]

    red_flaref11320.JPG
    Subscribe to see EXIF info for this image (if available)
     
  2. pdh

    pdh Mu-43 Top Veteran

    598
    May 6, 2010
    it will help to say what camera and lens you used, and any post-processing that was applied
     
    • Like Like x 1
  3. blue

    blue Mu-43 Veteran

    281
    Jun 1, 2010
    UK
    jpeg straight out of camera. G1 with Leica Elmarit 45mm.
     
  4. BBW

    BBW Super Moderator Emeritus

    What software for the photo? It reminds me of something that I've noticed happening on some of mine if I have tried to bring down the highlights... I realize that you are not doing that but I do think the software might be doing it.
     
  5. blue

    blue Mu-43 Veteran

    281
    Jun 1, 2010
    UK
    No software that I have used. This is straight out of the camera. You could see it in review on the camera itself. (I have no RAW at the moment).
     
  6. trisberg

    trisberg Mu-43 Regular

    69
    Apr 14, 2009
    Take a look at Fig 6 in this link http://toothwalker.org/optics/bokeh.html

    "Figure 6. A cropped image that shows the double-line effect (nisen-bokeh) in the blurred background due to overcorrected spherical aberration. Photograph by Jiawei Ye."

    Looks similar IMO.

    -Thomas
     
    • Like Like x 1
  7. blue

    blue Mu-43 Veteran

    281
    Jun 1, 2010
    UK
    Thanks for the link trisberg - though on first reading most of it has gone straight over my head ! I'll study it some more.

    I'm still not sure why the effect is so pronounced just on the poppy flowers. The rest of the oof/bokeh areas - stalks, flower heads, twigs are OK to my eye.
     
  8. BBW

    BBW Super Moderator Emeritus

    Obviously, this is way beyond my scope. Thank you trisberg! blue, please report back in after you've had a chance to study the information some more.

    The whole distortion concept is something that I know little of and feel I understand even less about...but I'm about to delve into it myself, a bit.
     
  9. alessandro

    alessandro Mu-43 Regular

    153
    Jan 29, 2010
    Nasty...
    But a RAW would be useful to investigate if it is a sensor/lens issue (the kind of spherical aberration and such), or if it's a limit of the jpg engine coping with oversaturated color and sharpening.
     
  10. Djarum

    Djarum Super Moderator Subscribing Member

    Dec 15, 2009
    Huntsville, AL, USA
    Jason
  11. alessandro

    alessandro Mu-43 Regular

    153
    Jan 29, 2010
    Could be, yes, but also looks like a cut off in the red channel, plus some sharpening artifact. The fact it's happening in the OOF portion seems to indicate the software found a border somewhere when the blown red starts to degrade. Also the in-focus flower shows sort of a red block. As I said, without seeing a RAW file I wouldn't exclude any explanation.
     
  12. blue

    blue Mu-43 Veteran

    281
    Jun 1, 2010
    UK
    Here's the RAW, and conclusion so far

    Well, a jpeg of the unprocessed RAW anyway. The effect is still there but not as pronounced.

    The light on the day was a brightish afternoon, not direct sun in this picture, but the poppies were glowing very red. On the red histogram there is a second peak to the far right - so "blown reds" is part of the problem with the jpeg engine in camera making it worse.

    [​IMG]

    I'm thinking still some lens aberration as well. Apparently ASPH lenses like this can show halos thanks to "over-corrected spherical aberration" and it is exacerbated in close up and conditions with bright areas in the picture.

    I found this link gives a nice explanation of some lens aberrations (if this helps anyone - BBW ?)

    Olympus Microscopy Resource Center | Lenses and Geometrical Optics - Common Optical Defects in Lens Systems (Aberrations)
     
  13. alessandro

    alessandro Mu-43 Regular

    153
    Jan 29, 2010
    Well, much much better! To the extent of not finding anything wrong: the merging of red and green is problematic to our eyes before giving the sensor a hard time...
    The proof is in the BW conversion: this version of the shot is not giving anything "strange".
    The terrific bokeh of the lens is the "culprit", creating a gradient between green and red.
     
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