Chromatic Aberration...

[D-B-J]

Thanks for the real world example to help me understand CA.

Regards,
Jake

 

[GooniesNeverSayDie11]

If you can't remove it all with the automated tools.. You can also zoom in on an area ( since it usually occurs between where there is high contrast ( dark meats light areas ) and open a saturation layer. Desaturate and then fill the layer mask with black to block the effect. Now zoom way in with a soft brush and paint the colored finge so that it desaturates it. This is not an ideal fix, but can help sometimes.

 

[JeffieLove]

How do you prevent it?
Inquiring minds want to know!

I'm copying this directly from the post:

ow to prevent:

Don't shoot from low looking up if you have open sky that will blow out. Your subjects will be ringed. If you have to shoot against a blown sky, narrow down a LOT - you don't have to shoot wide open if there's nothing in the background but blown sky. And try to shoot from a direction that doesn't have blown sky. Good photographers move with their subjects to always keep the right background behind them. New neophyte photographers stand there and shoot while the subject moves - and then complain about blown skies and fringing.

CA happens most when you have something dark against an area that is blown. Avoid shooting in a way that gets

Similarly, don't put your subjects in front of a white or bright items (e.g., house or wall) and shoot wide open - epic fail.

Make sure your subject doesn't wear items like white hat or bows on top of the head outdoors. Those will either blow out or will have massive CA since the light on most days comes from above (especially overcast days).

Don't overexpose. It's that simple. Get your exposure tighter and don't over or underexpose.

This subject tends to come up a lot in Winter since there are a lot of grey overcast days that cause CA. The way the light diffuses on those days can really contribute to CA incidents.

As a further note on technical issues:

Superior coatings to prevent fringing and flaring is a hallmark of many, if not most, new lenses. It is one of the reasons to buy the best lens possible. But there's some controversy on that subject too - you can't blame it on a poor lens since it is something that happens on the sensor.

What it amounts to for us guys is that you're going to find fringing most commonly on crop sensor cameras. This has to do with DSLRs having special sensors to capture the greens (traditionally the sharpest channel) - and in doing so, light wavelengths can overlap on crammed digital sensors and create the fringing.

If you are really worried about it, don't shoot wide open or fully closed down. Shoot 2-3 stops above your lens' widest aperture. And try to work your way up to a full frame camera (D700 or 5D) as soon as you can. Crop sensors have much higher instances of CA and noise than full frames do (a result of pixel contamination from sensor pixels being packed so close to each other).

And just remember that fringing occurs on backlight dark areas (high contrast areas) - a person against a blown out sky will fringe if shot wide open, for example. This applies to backlight hair, trees with a blown sky, even a shirt with black and white bold stripes if shot too bright.

You can't fix it easily at all in RAW - so make sure your exposure counts.Compromise and not shoot fully ETTR if it means there will be a blown area anywhere in the image. And shoot smartly to avoid blown skies or bright objects around or behind your subject. Avoid patchy sunlight.

 

[JeffieLove]

If you can't remove it all with the automated tools.. You can also zoom in on an area ( since it usually occurs between where there is high contrast ( dark meats light areas ) and open a saturation layer. Desaturate and then fill the layer mask with black to block the effect. Now zoom way in with a soft brush and paint the colored finge so that it desaturates it. This is not an ideal fix, but can help sometimes.

I ended up fixing it along the tree with the clone stamp mostly. I also used a hue/desaturation layer and desaturated the cyans and greens.

I fixed the magenta/purple spot in his hair with a hue/desaturation layer and desaturated magentas.

 

[dxqcanada5]

Digital cameras use one sensor capture the three colors on different layers ... Blue, Green, Red.
Lenses are designed to focus all wavelengths of light at the same point ... so this mean the top layer color is the most focused of the three.

A foveon sensor has a single layer, so would not suffer from this.
In the future, foveon sensors would be the norm (Sony is actively working on this).

 

[JeffieLove]

And here's the fix

 

[Robin Usagani]

If you are lazy... make it black and white .... Tadaaa! LOL

 

[JeffieLove]

Psh, I'm not that lazy when it comes to making pictures look good though... and I just finished going through this whole photo shoot... all 100 photos have CA in them I wanna cry

 

[RauschPhotography]

Looks much better now!

 

[dxqcanada5]

What lenses were you using in that shoot ?

 

[JeffieLove]

Just the 85mm f/1.8...

Here's my "rant" on it copy/pasted from another forum where I post...

I'm now going through the rest of the photos from this shoot to see if they all have CA... They do... Even the shots where it is a white handrail about 6 feet in front of a white house... Why would that have CA??? Other than shooting wide open...

So that leads me to another question of...

What good is a lens that has that aperture if you can't shoot at that wide aperture without getting CA which is almost unfixable?

I'm ready to get rid of my 85mm now lol This was the first full session I shot with it and I'm beyond disappointed. If I can't use all the capabilities of the lens, what's so good about it?

 

[JeffieLove]

Should I be concerned with the CA and getting rid of it if you can't see it without zooming in on the picture? These more than likely won't be printed any bigger and 8x10...

 

[dxqcanada5]

Canon EF 85mm f/1.8 USM Retest @ 15mp / Review - Analysis

"Purple Fringing
We've already reported the problem before but the EF 85mm f/1.8 USM is somewhat prone to purple fringing at extreme contrast transitions. The issue is primarily limited to f/1.8 so you can work around it in critical scenes."

Birefringence of EF 85mm f/1.2L II

 

[Robin Usagani]

Well, you can start by not shooting wide open when it is bright like that. If your subject is close and the background is pretty far, the background will still be pretty fuzzy with smaller aperture.

 

[JeffieLove]

Canon EF 85mm f/1.8 USM Retest @ 15mp / Review - Analysis

"Purple Fringing
We've already reported the problem before but the EF 85mm f/1.8 USM is somewhat prone to purple fringing at extreme contrast transitions. The issue is primarily limited to f/1.8 so you can work around it in critical scenes."

Birefringence of EF 85mm f/1.2L II

I was shooting at f/2, so not technically wide open... But I'm getting more green/magenta fringing than purple.

Well, you can start by not shooting wide open when it is bright like that. If your subject is close and the background is pretty far, the background will still be pretty fuzzy with smaller aperture.

I figured that much, but what's the point of having a lens with such a wide aperture capability if you can't use it???