Lens Corrections - CA

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pochito

Active member
Supporting Member
Chromatic Aberration
Some of my lenses produce under circumstances some fringing, reddish or bluish or both.
I try to correct this in LR on the panel "Lens Corrections" -Remove Chromatic Aberration. Sometime automatic, sometimes using the manual mode.
I understand why CA occurs but I am not sure of what the application (in this case LR) is doing
Is it just desaturating those colors, doing some real lens correction based on the data from the lens or something else?
Is this procedure affecting the rest of the image?
Anybody knows or knows where to look for info?
Thank you
 

bleirer

Well-known member
Supporting Member
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tclune

Member
My understanding is that CA comes in two flavors -- lateral and longitudinal. In lateral CA, (which looks red on one side and blue on the other) the lenses focus the different sensor colors on the same focal plane, but shifted left, right, up or down from each other. Longitudinal CA focuses the different colors on different planes, resulting in blurry edges of the unsharp red and blue combined ("purple fringing.") My guess is that there's probably a bit of both in any CA. Anyway, lateral CA should be able to be corrected by shifting the different colors' sensor data to line back up with each other. LoCA, OTOH, involves two of the color sensor arrays not being in focus, which seems less tractable in software. But I could be failing to properly think this through. It wouldn't be the first time.
 
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bleirer

Well-known member
Supporting Member
My understanding is that CA comes in two flavors -- lateral and longitudinal. In lateral CA, (which looks red on one side and blue on the other) the lenses focus the different sensor colors on the same focal plane, but shifted left, right, up or down from each other. Longitudinal CA focuses the different colors on different planes, resulting in blurry edges of the unsharp red and blue combined ("purple fringing.") My guess is that there's probably a bit of both in any CA. Anyway, lateral CA should be able to be corrected by shifting the different colors' sensor data to line back up with each other. LoCA, OTOH, involves two of the color sensor arrays not being in focus, which seems less tractable in software. But I could be failing to properly think this through. It wouldn't be the first time.
Good explanation! Reminded me of an article I had read a while back.

 

bleirer

Well-known member
Supporting Member
If one wants more control over the selected area, there is a lens correction filter in Photoshop which could be used with a mask to only apply to a part of the image. I'm not sure if this filter would work on a smart object, but if so converting the layer first to a smart object would be the nondestructive way, otherwise just duplicate the layer and work on the duplicate with a layer mask.

There is also a more complex way that involves adding a Gaussian blur, changing the layer mode to color, and painting out the affected colors (I've not tried it).

 

pochito

Active member
Supporting Member
Thread starter
Thank you very much Bill and tclune. Your information covers very well what I wanted to know :D
 
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