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Here is an unexciting test shot of some ducks in a river, taken in bright sunlight:

enter image description here

In the foreground, the highlights have a distinctly pink cast. I am certain they weren't pinkish in reality, since it's a reflection of the sun. The white balance was set automatically by the camera and appears to be correct. (It's almost identical to Lightroom's 'daylight' white balance preset.)

Additionally, in the following picture (which is slightly out of focus) the highlights appeared greenish:

enter image description here

I suspect it has to do with chromatic aberration, since they seem to come out greenish when the focal plane is in front of the water and pinkish when it's behind it. However, checking the "remove chromatic aberration" box in Lightroom doesn't seem to have any effect on these images.

I haven't observed this in my shots before, but is it a common thing to happen? I just bought this lens second-hand and I can return it this week if there is a problem with it, so I'd like to know if that's the case.

On the other hand, if this is normal and expected, what should I do to avoid this result in future?

If it makes a difference, these images are rendered from RAW files using Lightroom, with all the settings left at their defaults. They were shot wide open, at f/2.4, which I realise was unnecessary in this situation. The lens is a Pentax 70mm limited prime.

  • You might try fiddling with the manual CA correction sliders (Defringe) in Lightroom. They can fix things that auto correction can't. In fact, the defringe control might be meant for exactly the problem you're having. – BobT Jan 18 '17 at 15:12
  • @BobT make it an asnwer. – Euri Pinhollow Jan 18 '17 at 19:46
  • @BobT thank you, that does seem to work, though I have to push the sliders to the extremes - it's good to know there's a way to fix it if it appears again. – Nathaniel Jan 18 '17 at 23:49
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    "... these images are rendered from RAW files using Lightroom, with no adjustments made to the images." There's no such thing as a raw file with no adjustments that can be viewed on a monitor. If you've made no adjustments, it just means you let the default profile you used to open the images in Lr make the adjustments for you. – Michael C Jan 19 '17 at 1:13
  • @MichaelClark of course - I meant that these are Lightroom's default renderings from RAW, with all the settings left on their defaults. – Nathaniel Jan 19 '17 at 3:42
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From : camerastuffreview.com

SECONDARY LONGITUDINAL CHROMATIC ABERRATION

This is a rare form of chromatic aberration. It gives a green color cast of blurred subjects closer than the point in focus and a purple color when subjects are behind the point in focus. All lenses can suffer from this phenomenon, but in general, fast lenses (with a larger aperture than aperture 2.8) are more sensitive to color bokeh. This form of chromatic aberration can be seen on the whole picture and cannot be corrected with chromatic aberration correction in Photoshop and Lightroom afterwards. Aperture does help against this phenomenon.

....in other words, this particular chromatic aberration occurrs along "Z" axis, whereas typically encountered CA occurrs in the plane of the "X-Y" axis.

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I think the effect you're seeing here is called blooming. Chromatic aberration happens because the lens focusses different colors at slightly different distances, so you usually get two different colors of fringing. Blooming apparently happens when the light is so intense that the charge on one part of the sensor travels to the surrounding area, and IIRC it can show up in your photos as fringes that are all the same color. Each one of those highlights is a reflection of the sun off the water, so it makes sense that blooming might be the problem -- the sun is much brighter than the rest of the scene.

If that's actually the cause of the pink highlights, you might be able to avoid it by underexposing a bit so that the highlights aren't quite so bright. A polarizing filter would also solve the problem.

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You might try fiddling with the manual CA correction sliders (Defringe) in Lightroom. They can fix things that auto correction can't. In fact, the defringe control might be meant for exactly the problem you're having.

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