enter image description hereRecently returned from Cape Town. A few of my pics show a thin reddish and green line running along the top of my Table Mountain shots. This is new to me! Any ideas?

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    \$\begingroup\$ The following would be helpful: Sample images demonstrating the problem. What camera, lens, and settings you used. \$\endgroup\$
    – xiota
    Commented Mar 3, 2019 at 9:42
  • \$\begingroup\$ Thanks. Will get an image from my deleted files. For these shots I used a Canon EOS 77D with a Tamron 18-300 lens. All were on the camera auto system linked to Landscape \$\endgroup\$
    – J Michael
    Commented Mar 3, 2019 at 9:53
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    \$\begingroup\$ Is this just a crop, or is it the entire image? \$\endgroup\$
    – jarnbjo
    Commented Mar 3, 2019 at 14:59
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    \$\begingroup\$ Can't find a 18-300 in Tamron's offering. There are 18-200, 18-270, 18-400 and a 16-300... So which is it? Some of them seem to suffer from heavy chromatic aberration. \$\endgroup\$
    – xenoid
    Commented Mar 3, 2019 at 15:34
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    \$\begingroup\$ Please post a full image, not a crop. \$\endgroup\$
    – xiota
    Commented Mar 3, 2019 at 16:43

2 Answers 2


The lens has a published focal length. However, each color comes to a focus at different distances from the lens. Red with its longest wavelength comes to a focus further downstream then violet which has the shortest wavelength. The lens maker attempts to mitigate by selecting a variety of different lens shapes. A concave lens displays the opposite chromatic aberrations from its convex counterpart. A modern lens is made by combining a strong positive with a weak negative. This combination, if well executed, places the red and violet focal lengths on the same plane. If not migrated, the red image is slightly larger than the blue image. All the other colors have different focal lengths -- thus each has a different size image. The image we get is a composite of all these different sized images. The color fringe you see is from a poorly corrected lens for chromatic aberration.

  • \$\begingroup\$ Or from an incorrectly 'corrected' image - if you'd apply the lens correction from the wrong lens model, it looks like that. \$\endgroup\$
    – Aganju
    Commented Mar 6, 2019 at 14:16

This is called, Spherochromatism. IGOOD =fast telephoto lenses when used wide open are prone to this. It happens when a FAST long lens is WIDE open

Outlines of out of focus WHITES are green in the background, and Outlines of out of focus WHITES are magenta in the foreground.

Solution Smaller aperture, has increased depth of field, so less out of focus.

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    \$\begingroup\$ There's both magenta and green in both foreground and background, and nothing looks particularly out of focus in the sample image. OP states used "Landscape" mode, which typically stop down the aperture. \$\endgroup\$
    – xiota
    Commented Mar 3, 2019 at 16:41
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    \$\begingroup\$ What does IGOOD mean? \$\endgroup\$
    – xiota
    Commented Mar 3, 2019 at 16:42
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    \$\begingroup\$ Something tells me that an 18-300mm lens is not going to qualify as “fast.” \$\endgroup\$
    – OnBreak.
    Commented Mar 3, 2019 at 19:25

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