Chromatic aberration... again!

[Abitconfused]

A lens may produce chromatic aberration that results in observable color fringing in areas of high contrast in an image. However, this color shift must degrade color accuracy throughout a larger area of the image than only the areas of readily observable fringing. In Camera Raw, does "Lens Corrections > Remove Chromatic Aberration" simply remedy the observable color fringing or make a more comprehensive color correction?

[Stagecoach]

Ed, in Camera Raw when removing the CA observable fringing (where we readily expect and see it) certain colours can be altered drastically.

I worked on an image the other week removing the CA from an edge between roof and very bright sky only to notice that a microphone foam cover within the frame had gone from blue to grey

[DanK]

There is also a local "defringe" option with the adjustment brush. However, I have read that this, unlike the global adjustment, is independent of the color range you might set on the global adjustment. Haven't tried it.

[Manfred M]

Chromatic aberration's most obvious effect is the coloured fringing, so removing those is important. Every lens has this to some extent, with the more expensive ones performing better in this regard than less expensive ones. The effect is a result of different wavelengths of light not focusing on exactly the same plane. There are actually two types of CA; axial (occurs along the optical axis) and longitudinal increases towards the edges (perpendicular to the optical axis). Axial CA can be corrected for by stopping down the lens as increasing the DoF reduces this issue; this has no effect on lateral CA. Removing the fringes is relatively easy but trying to do more would do more damage to the image data than the relatively minor impact you are concerned with.

Removing this effect during the import process is the easiest way to handle this and no, ACR / Lightroom and all of the other raw converters only take care of the fringing only. As Dan has pointed out, removing it later in PP is no fun at all and very labour intensive. Most people (including me) leave the "Remove CA" turned on by default. I use a second line of defence and that is by exporting my ACR output to Photoshop as a SmartObject. That lets me go back into ACR and tweak the CA removal manually when the automated function has not done a good enough job, which can sometimes happen.

[Abitconfused]

So it’s fair to say that chromatic aberration does impact image quality (sharpness, color, contrast) but a good Raw processor will address fringing and make us feel a little better about the product if not the lens?

[proseak]

The hard part is finding "a good Raw processor" - I've found that Adobe is OK, but not great with my cheapish superzoom Sigma. Fringes were mostly suppressed, but sharpness suffered. DxO does a lot more to recover matters; you might give their free trial a go.

[pschlute]

in certain circumstances you may be able to deal with CA better by using another tool. CA is often found where you have tree branches against a cloudy sky. In Photoshop, using a soft brush, paint out the colour in the areas where you have CA showing. It won't work for all scenes but on certain ones can be very effective.

[Shadowman]

So it’s fair to say that chromatic aberration does impact image quality (sharpness, color, contrast) but a good Raw processor will address fringing and make us feel a little better about the product if not the lens?

Ed,

How I feel about the lens is based on other factors (sharpness, focus options, etc), when it comes to CA my thoughts are more about the software options available to correct (as much as possible) the issue.