PS - Chromatic Aberration Darkening of Shadow?

Question

I've notice this effect in pics using either my Nikon D500 or Z6 with a Z50mm 1.8 S lens. My images are all recorded raw, and with whatever negliable sharpening Nikon applies to raw files. I can feed the raw file into Nikon NX Studio or Adobe Camera Raw and then PS but, regardless of the workflow... the same unwanted shadowing appears.

This appears before I apply any sharpening in the apps.

The transition area that is out-of-focus acquires a slight darkening border of sorts. I've adjusted various lens correction sliders in all apps to no effect. So, I don't know if it this issue is chromatic aberration or something else.

In the past I've made selections of the troublesome areas and cloned in tones from similar areas. The end result doesn't always work, and seems like a crude hack anyway. In the attached detail pics, the issue may not appear objectionable, but it is in viewing the entire image as a whole.

Any ideas?

I use the latest MACOS on a iMac24, and PS 26.2.0

LAMY2017 · Accepted Answer

The goal is a B&W image. The problem area is where the shoulders meet the green grass in the background.

The Nikon Z 50mm 1.8 S is exceptionally sharp, and perhaps that is part of the problem.

*The uploader gives this error msg when attaching a NEF file. "The attachment's jan18 - a0007.nef content type (image/x-nikon-nef) does not match its file extension and has been removed"

So, attached is a PSD with no adjustments from ACR or in PS.

I opened the psd, and now I feel the need to amend my previous comments. I know the superusers here will enjoy shooting down my crazy idea, but I don't think it's CA at all, but contamination from light bounced off the grass. The f/2 aperture blurred it. I zoomed in to 500% and don't see any fringing in his hair, eyelashes, etc. If CA was present as a result of a lens or post-processing, it would be everywhere.

D Fosse · Answer

Axial chromatic aberration produces color fringing in out-of-focus areas. Usually it's magenta in front of the focus plane, and green behind the focus plane. This is an optical property of the lens, irrespective of any processing. Axial chromatic aberration is easy to recognize and hard to fix. Some lenses are better than others, and truly "apochromatic" lenses are extremely expensive. Most of us just try to live with it and repair when too obvious.

Depending on the type of B&W conversion, this fringing may exhibit as tonal changes. The RGB model desaturates by a simple average of numbers, so purples go light and yellows go dark and muddy. A Lab conversion preserves inherent luminosity in colors, so may often produce better results.

Personally I'm not impressed by Lightroom/ACR defringe, because it tends to produce very visible edges. For critical use I prefer to do it in Photoshop. A simple and often surprisingly effective way is to add a duplicate blurred layer in Color blend mode, then paint out the fringed areas in a layer mask.

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