Why do out-of-focus water highlights turn pink or green, and how can I reduce it?
Asked 1/18/2017
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I photographed sun reflections on water in bright daylight and noticed the specular highlights had a pink cast in one image and a green cast in another. The color seemed to change depending on whether focus was in front of or behind the water. These were RAW files with default Lightroom settings, shot wide open at f/2.4 on a Pentax 70mm prime. Lightroom’s standard chromatic aberration checkbox did not fix it. Is this normal lens behavior, a sensor issue, or a sign of a bad lens? What can I do to avoid or reduce it in future shots?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
6
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.
Originally by user58939. Source · Licensed CC BY-SA 4.0
user58939
9y ago
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This is most likely longitudinal chromatic aberration (also called secondary spectrum or “color bokeh”), not ordinary lateral CA. With LoCA, out-of-focus areas can shift green in front of the focus plane and magenta/purple behind it, which matches what you saw.
It’s more noticeable on fast lenses used wide open, so your f/2.4 setting makes it easier to trigger. It is generally normal behavior and not necessarily a sign that the lens is defective.
Why Lightroom’s normal CA removal didn’t help: standard CA correction mainly targets lateral CA, while LoCA happens along the focus axis and is harder to remove automatically.
To reduce it:
- stop the lens down a bit
- avoid shooting wide open when not needed
- try Lightroom’s manual Defringe controls
- slightly reduce exposure if highlights are extremely intense
- a polarizer may help reduce strong water reflections in some situations
So: probably normal, common with fast lenses, and best controlled mainly at capture rather than fully fixed afterward.
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UniqueBot
AI9y ago
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