What is Chromatic Aberration?
Chromatic Aberration, also known as “color fringing” or “purple fringing”, is a common optical problem that occurs when a lens is either unable to bring all wavelengths of color to the same focal plane, and/or when wavelengths of color are focused at different positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colors of light travelling at different speeds while passing through a lens. As a result, the image can look blurred or noticeable colored edges (red, green, blue, yellow, purple, magenta) can appear around objects, especially in high-contrast situations.
In this article we’ll understand its causes and learn ways to easily avoid it both while shooting and in post-production. The picture presented below which relates to my previous post, where the Minarets were shot against a bright sky, resulting in a bad case of purple and green fringing. Color fringes may also be caused by other factors such as lens flare or the camera’s sensitivity to the different wavelengths of light but since CA is the most common cause.
How to Reduce Chromatic Aberration in field
Avoid high contrast situations
This might seem like a no-brainer but it really helps to downplay the optic design imperfections, especially if using consumer level lenses like most of us do. Common suspects include fences, tree branches and shooting a subject against a bright sunny sky.
Stop down your aperture
While it is very tempting to use a wide aperture to get nice bokeh, if you get some fringing try to stop down the aperture at least one stop. This will greatly help minimize the visible aberrations.
Avoid the extremes of your zoom lens
Not only in life but also in photographic lenses it is said that virtue is in the middle. Zoom lenses usually perform better when using its middle focal lengths. For example, when using a 70-200mm zoom, shooting at 135mm will usually wield better results than at 200mm.
Avoid super zoom lenses
Unless you don’t want to carry extra weight, like when going on vacations, avoid super zooms at all costs. They have terrible chromatic aberrations on the wide end. Alternatively, get some prime lenses, as they are generally optimized to reduce these optical artifacts and are relatively cheaper and lighter.
How to Reduce Chromatic Aberration for HDR
Anyone has use this technique to reduce the CA. But for HDR photographers, CA removal is very important as if the CA is not reduced, it will be amplified. To ultimately reduce chromatic aberrations in your HDR images, I recommended to first convert your RAW exposures, in any prefered method prior to combining them in Photomatix Pro. The process reducing chromatic aberrations on your source images prior to sending to HDR software is the best method, rather than simply checking the box within Photomatix to reduce chromatic aberrations will not completely remove them.
Using Adobe Camera Raw
This is the method I use for most of my pictures. The first step you need to do is click on one of the set of the bracketed shots and open in Camera Raw to see if your photo has CA. For this example, lets take my previous post and lets zoom over and here can see the the Green and Magenta CA.
Next, in the camera raw, head over to the Lens Correction tab as shown below and once this tab is selected you need to click on the submenu tab the Color.
All you need to do is check the box “Remove Chromatic Aberration” and you should see the CA gone but it will not go off complete and hence you need move the sliders Purple Amount and Green Amount as necessary. For the above image the below setting of 5 for the purple was more than enough.
Finally make sure you keep moving around the images to check for any remaining CA to fine tune your images. Once you remove the CA here in Camera Raw, i would advise you to still tick the “Reduce CA” in Photomatix.
Using Adobe Lightroom
Lightroom has the similar controls like Adobe camera raw. Once you have imported the picture in Lightroom and you are in the Develop Module, just come down to the section Lens Correction and select the sub menu “Color”. Follow the similar steps i mentioned above and you should be able to get rid of the CA. Just make sure that you dont touch the Purple Hue and Green Hue.
Using Adobe Photoshop
Finally you can also remove the CA using photoshop. To access this option, you need to choose the Filter>Lens Correction in the Photoshop Menu
and then you need to select the custom option tab to come to the setting of the CA.
Depending on your image, you should try to correct the fringing in the best way you can by adjusting the sliders. To do this in an optimal way make sure you are viewing the image at a magnification of 100% or more.You might have to move only one or both sliders: it all depends on the image you’re dealing with. In this case, I had to move both.
I have found Adobe Camera Raw and Lightroom to be the best options to reduce the CA. For HDR photographers, as explained before it is better to remove the CA before feeding it to any HDR softwares. There are other softwares which i have not mentioned that can reduce the CA but i have no or little know how of this to explain it here.
Meanwhile you can learn more about processing black and White photos here
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