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Re: [PanoToolsNG] Chromatic Aberration on fisheye lenses images (comparative test)

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  • Serge Maandag (yahoo)
    ... That s a weird result... You would expect the blue abberation to be more pronounced under light that simply contains a bigger part of the blue spectrum.
    Message 1 of 6 , Jul 1, 2007
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      > Six different fisheye lenses have been subjected to a comparative
      > test in order to assess their respective propensity to TCA.
      > The influence of light illumination spectrum on TCA has also been
      > studied.
      >
      > You may read the report here:
      > http://tinyurl.com/32jjdz

      That's a weird result...

      You would expect the blue abberation to be more pronounced under light that simply
      contains a bigger part of the blue spectrum. But not that the light source would
      change the scaling of the abberation.

      Do you think this would happen in a single element lens too? Or is it a side product
      of the compounding of elements?

      Serge.
    • Rik Littlefield
      ... Serge, The thing to remember is that the aberration depends on wavelength, not just on red versus green versus blue . Two different wavelengths may
      Message 2 of 6 , Jul 1, 2007
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        --- In PanoToolsNG@yahoogroups.com, "Serge Maandag (yahoo)"
        <yahoo@...> wrote:
        >
        > > Six different fisheye lenses have been subjected
        > > to a comparative test in order to assess
        > > their respective propensity to TCA.
        > > The influence of light illumination spectrum
        > > on TCA has also been studied.
        > >
        > > You may read the report here:
        > > http://tinyurl.com/32jjdz
        >
        > That's a weird result...
        >
        > You would expect the blue abberation to be more pronounced
        > under light that simply contains a bigger part of the
        > blue spectrum. But not that the light source would
        > change the scaling of the abberation.

        Serge,

        The thing to remember is that the aberration depends on wavelength,
        not just on "red" versus "green" versus "blue".

        Two different wavelengths may both record only in the "blue" channel,
        but nonetheless be shifted by different amounts.

        What gets recorded in the "blue" channel is a kind of weighted
        average of the shifts over all of the different "blue" wavelengths
        that were present in the illumination.

        If the different light sources have different proportions of various
        wavelengths in the "blue" band, then those sources will show
        different TCA.

        In summary, it is the detailed shape of the spectrum -- where are the
        peaks and valleys? -- that cause TCA to be different for different
        light sources.

        The phenomenon called "metamerism" is due to a similar cause. Much
        info about that can be found by googling. A good place to start is
        to Google "define: metamerism" and to read
        http://en.wikipedia.org/wiki/Metamerism_(color) .

        --Rik
      • michel thoby
        http://tinyurl.com/2zzjsl Based on other experiment that you may replicate, I have proposed some additional conjectures on the same subject. Regards, Michel
        Message 3 of 6 , Jul 2, 2007
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          http://tinyurl.com/2zzjsl

          Based on other experiment that you may replicate, I have proposed
          some additional conjectures on the same subject.

          Regards,

          Michel


          Le 1 juil. 07 à 20:03, Rik Littlefield a écrit :

          > --- In PanoToolsNG@yahoogroups.com, "Serge Maandag (yahoo)"
          > <yahoo@...> wrote:
          > >
          > > > Six different fisheye lenses have been subjected
          > > > to a comparative test in order to assess
          > > > their respective propensity to TCA.
          > > > The influence of light illumination spectrum
          > > > on TCA has also been studied.
          > > >
          > > > You may read the report here:
          > > > http://tinyurl.com/32jjdz
          > >
          > > That's a weird result...
          > >
          > > You would expect the blue abberation to be more pronounced
          > > under light that simply contains a bigger part of the
          > > blue spectrum. But not that the light source would
          > > change the scaling of the abberation.
          >
          > Serge,
          >
          > The thing to remember is that the aberration depends on wavelength,
          > not just on "red" versus "green" versus "blue".
          >
          > Two different wavelengths may both record only in the "blue" channel,
          > but nonetheless be shifted by different amounts.
          >
          > What gets recorded in the "blue" channel is a kind of weighted
          > average of the shifts over all of the different "blue" wavelengths
          > that were present in the illumination.
          >
          > If the different light sources have different proportions of various
          > wavelengths in the "blue" band, then those sources will show
          > different TCA.
          >
          > In summary, it is the detailed shape of the spectrum -- where are the
          > peaks and valleys? -- that cause TCA to be different for different
          > light sources.
          >
          > The phenomenon called "metamerism" is due to a similar cause. Much
          > info about that can be found by googling. A good place to start is
          > to Google "define: metamerism" and to read
          > http://en.wikipedia.org/wiki/Metamerism_(color) .
          >
          > --Rik

          >
          >



          [Non-text portions of this message have been removed]
        • Serge Maandag (yahoo)
          ... Ah, it is sort of like a quantification error. Then I just got Michel wrong. This does sound logical to me. I can imagine colours leaning towards infrared
          Message 4 of 6 , Jul 2, 2007
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            > What gets recorded in the "blue" channel is a kind of weighted
            > average of the shifts over all of the different "blue" wavelengths
            > that were present in the illumination.

            Ah, it is sort of like a quantification error. Then I just got Michel wrong.
            This does sound logical to me. I can imagine colours leaning towards infrared or
            ultraviolet could have a substantial influence.

            > In summary, it is the detailed shape of the spectrum -- where are the
            > peaks and valleys? -- that cause TCA to be different for different
            > light sources.

            I believe ignited-gas lamps usually have weird peaked spectrums, so I can imagine
            them causing these weird aliasing type of effects.

            > The phenomenon called "metamerism" is due to a similar cause. Much
            > info about that can be found by googling.

            Ah, I knew the effect, but not the name.

            Thanks for the great explanation (as usual)!
            Serge.
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