Chromatic Aberration

Nikon 1.4G 50mm + D300

Foto geschoten op Iso: 200, A priority:F1.4, S:1/2500

100% crop JPG origineel


bewerkte RAW versie


Histogram:


Highlight clipping warning:


Exposure teruggebracht, geen highlight clipping meer:


Resultaat 100% crop: -0,55 exposure reductie (geen highlight clipping meer aanwezig) 100% kleurruisreductie toegepast op 16 bit RAW file, daarna 100% kleurruisreductie via filters in PS zelf.


http://www.bythom.com/Nikkor50AF-Slensreview.htm
"Chromatic aberration: Lateral chromatic aberration (side to side) is negligible wide open, with a tendency to slightly increase in visibility as you stop down, but it's never at levels I really worry about. More interesting is longitudinal chormatic aberration (near/far, sometimes called axial CA). The 50mm f/1.4G AF-S most certainly exhibits such aberrations, especially near maximum aperture. Objects closer than focus get a magenta cast, objects further than focus get a green cast. This is not unusual for a fast prime, and I suspect Nikon's adding axial chromatic aberration correction to Capture NX2 was due to this lens. Not a terrible flaw, but one to be aware of."

Photo.net - Andreas Manessinger , Apr 17, 2009; 06:14 p.m.:
"CA comes in two flavors, lateral and longitudinal.

Lateral CA comes from the fact that the focused image has different sizes for different wavelengths. You can easily correct it in any RAW converter, and for JPEGs your D90 does it automatically. You see lateral CA as fringes around twigs that have different colors on different sides of the twigs, one side green, the other magenta, but blue/yellow may also be seen. Lateral CA are no problem in the center, but increase towards the corners.

Longitudinal CA can't be corrected in software. They come from the fact that the focus for different wavelengths lies on different planes, i.e. when green is focused on the sensor, red is focused in front of the sensor and blue behind. Or vice-versa. Does not matter here. Longitudinal CA are everywhere in the image, not only near the corners. They can be seen as green fringes around out-of-focus background objects and magenta fringes around out-of-focus foreground objects. The fringes have the same color on all sides, they only depend on the distance, the amount by which the object is out of focus and the aperture. The bigger the aperture (the smaller the number), the stronger are the longitudinal CA.

It is hard and expensive to correct a lens for both kinds of CA. Lens makers don't seem to care much about lateral CA today. the cameras begin to correct it automatically and it is not more than a slight nuisance. They normally concentrate on longitudinal CA, but even that is hard to correct for a lens used wide open. The faster the lens (i.e. the bigger the aperture), the worse the problem. If you look at tests of the very expensive and highly regarded Canon 50/1.2L, you will see that it has much stronger longitudinal CA than the Sigma 50/1.4. That's just the way it is. You can spend $4000 or more on Leica lenses that are better in that regard, but that's about the only thing that you can do.

In fact the Sigma 50/1.4 has significantly less of both kinds of CA than the new Nikon 35/1.8, about the same lateral CA as the new Nikon 50/1.4G and significantly less longitudinal CA than the Nikon 50/1.4G.

This leaves purple fringing. That is a different phenomenon, and it is most apparent on highlight edges, normally only on one side of twigs, it is strongest in the corners, and it is connected to overexposure. If you correctly expose for the sky, it should go away. It will also go away if you stop down. It's the combination of wide open lens, overexposure and contrast edges that triggers it. It is also not only a lens problem, it seems to be connected with digital sensors as well. In fact it does not happen with film.

If you post a crop from the corner, we probably could diagnose the problem, but if it is purple fringing, it just is that way under those circumstances. Avoid the circumstances and you avoid the problem.

I have no particular experience with purple fringing on my Sigma 50/1.4, but I am sure with the right combination I could trigger it as well. It is much less than in older Nikon lenses like my AF 24/2.8 or AF 85/1.8D, but it may be there.

Now specifically to your questions: No, it's physics. The design of the Sigma 50/1.4 is class-leading. You may get better lenses, but not even remotely in that price category.

Lateral CA can be fixed in software, longitudinal can not. In case of severe purple fringing, I normally use a Hue/Saturation layer with a mask to selectively desaturate blue and magenta where it is strongest. That's about the only thing that is possible.

No idea about the warranty, but it does not seem to be a case of a defective lens (though an image would help to verify it).

I suppose I'd have a similar problem under similar conditions, and I suppose I'd have it with pretty all my lenses that open up that wide.

The Nikon 50/1.4G won't help you a bit."