Chromatic Aberration Correction.

[Dinarius]

I'm curious to know to what extent CA correction is part of the workflow of other board members.

I find the ACR controls a bit unwieldy. But, I may not be using them to the best of their ability. (I do move the default sharpening slider to zero beforehand!   )

Is CA correction image specific, or can default settings be used for certain lens/aperture combinations?

How much of a difference does it make to image sharpness? (How long is a piece of string, I suppose.) But, given that pixel count is racing ahead of lens quality (dare I mention the 1Ds Mk3?! Yes, I own one.) I think that any issue relating to sharpness is relevant.

Can someone point me in the direction of a decent tutorial?

I'm bringing this up because I think it's overlooked, and it is rarely discussed. (I did a search on this site and the hits were old and unhelpful.)

Many thanks.

D.

[lightstand]

remember to hold down the option key on a mac when moving either the red/cyan or blue/yellow slider to see the effect.

[thompsonkirk]

In my experience zoom lenses are much more susceptible to CA than primes, & almost always require CA correction.  You can use other programs than ACR (including PS Filters>Lens Distortion), but it seems to work as conveniently as any other.  The amount of correction can vary with the focal length to which you've  zoomed, so there's no standard/default setting that you can incorporate into ACR/Lightroom camera defaults.  It's one image (or batch of like images) at a time.  

Kirk

PS:  Remember, if you do both capture & output sharpening, that CA correction should happen prior to capture sharpening.

[Misirlou]

With C/A, I usually find a small detail (like a leaf or a small stone) near a corner of the frame, since it's easier to see C/A in the corners than the center. Zoom in to 1:1 or even higher magnification (the Ctrl+0 and Ctrl/Alt+0 key combos are most helpful). You want to hold down the Alt key (on a PC) while using the C/A sliders, which filters the colors down to what the slider is actually adjusting. Then just adjust the slider until the colors on both sides of the subject detail look the same. If you hold down the Alt key, it's really easy to see. Then go to the other slider and repeat. It's a good idea to look around the frame and verify that the adjustment is good everywhere, because other forms of fringing sometimes interfere with C/A.

You won't see the benefits in small prints a lot of the time. But if you print large, or crop a lot, it can really make a big difference. I use a C/A correction on most shots, generally because I can only afford crappy lenses, and most of my shots need some. I don't get very worked up about distortion either, because that's easy to correct too.

[NikoJorj]

Is CA correction image specific, or can default settings be used for certain lens/aperture combinations?
[a href=\"index.php?act=findpost&pid=178669\"][{POST_SNAPBACK}][/a]

Both!
It is fixed for a given lens/focal length, a given aperture and a given focus distance - but as far as I know, the focus distance is a second or third order factor, and lens is the big key.
I find that for my EFS 10-22 eg, a generic correction (about -15/+15) is almost correct for all settings... I'd love to see an automated correction for that in LR, but with the metadata browser it's not very hard to apply.

It is fixed, but you may not always see it - you need a contrasty and in-focus detail far from the center to see it (and therefore to fix it - better be at 300% zoom btw).
Of course, the more you do some local contrast enhancing and sharpening, the more you'll see it. I tried the DOP detail enhancer recently, and it made it really flash in a A4 (letter) print - there was a bush surrounded by snow in the corner of the frame.

[bjanes]

I'm curious to know to what extent CA correction is part of the workflow of other board members.

I find the ACR controls a bit unwieldy. But, I may not be using them to the best of their ability. (I do move the default sharpening slider to zero beforehand!   )

Is CA correction image specific, or can default settings be used for certain lens/aperture combinations?

How much of a difference does it make to image sharpness? (How long is a piece of string, I suppose.) But, given that pixel count is racing ahead of lens quality (dare I mention the 1Ds Mk3?! Yes, I own one.) I think that any issue relating to sharpness is relevant.

Can someone point me in the direction of a decent tutorial?

I'm bringing this up because I think it's overlooked, and it is rarely discussed. (I did a search on this site and the hits were old and unhelpful.)

Many thanks.

D.
[{POST_SNAPBACK}][/a]

Here is one [a href=\"http://www.photos-of-the-year.com/articles/adobe-raw/]Tutorial[/url] that may be helpful in addition to what other posters have added.

Chromatic aberration is most marked with wide angle and telephoto lenses and also is present in many zoom lenses. It can be reduced with special types of glass, such as the ED (extra-low dispersion glass) on the more expensive Nikkor lenses and UD (Ultra-Low Dispersion) on Canon lenses. Sigma and some other independent vendors use the term apochromatic to refer to lenses with better correction of chromatic aberration. These lenses should pose less of a problem with CA.

With ACR, you have to enter the correction values manually and judge the effect in real time by eye. If you use the camera manufacturer's raw converter (e.g. Nikon Capture NX) can read the lens meta data and apply the correction automatically according to a lens database that has the required values. The Nikon D3 can read the lateral color in the image and apply the correction automatically, even with non Nikon lenses for which there is no data base. This feature works with JPEGs and the equivalent correction can be applied with Nikon Capture NX with raw files.

Bill

[Dinarius]

Bill,

That tutorial is just what the doctor ordered!  

Many thanks.

D.

[Philmar]

PS:  Remember, if you do both capture & output sharpening, that CA correction should happen prior to capture sharpening.
[a href=\"index.php?act=findpost&pid=178765\"][{POST_SNAPBACK}][/a]

Does ACR know enough to do the CA correction BEFORE the capture sharpening?

[b2martin]

I generated a set of presets for ACR (Adobe Camera RAW) at various focal lengh settings that does a very good job of correcting CA.  My first step in processing images is to select the preset for each image.  

I generated these by shooting images of a chain length fence at the various focal lengths and adjusting CA with the image at 200% and at the far edge of the long side.