In the photo above, you may notice that the colors on the left-hand side appear to be showing fringes of green and red along the sharp edges of the subject; this is what is called chromatic aberration.
What is chromatic aberration?
Chromatic aberration (also known as color fringing or dispersion) is a common problem in lenses which occurs when colors are incorrectly refracted (bent) by the lens, resulting in a mismatch at the focal point where the colors do not combine as they should.
To help understand this a bit better, remember that the focal plane is your sensor’s point of focus; where all the light from your lens should rejoin together to be correctly detected by your sensor. The thing is, depending on the construction of your lens, your chosen focal length, and even the aperture that you’ve used, certain wavelengths (colors) may arrive at points before or after where the focal plane sits.
When this occurs, you end up with the telltale color fringing around edges in your photograph; and although you can remove low levels of chromatic aberration in Photoshop and Lightroom, the reality is that each extra moment you spend on touching up a photograph is one moment less you have to get something else done!
Why does chromatic aberration occur?
Chromatic aberration happens because your lens acts as a prism; bending light depending on the various properties of the glass, and much like the triangle-shaped one made famous by Pink Floyd, colors passing through it are split at different angles.
Remember that light is actually made up of several different wavelengths (colors). So, for your camera’s sensor to detect the combined color of light, your lens needs to make all wavelengths of that particular ray hit the exact same point on your sensor.
This sounds simple, but you need to take into account the fact that various wavelengths (and thus various colors) will be striking your lens all at once and that each of these rays will behave slightly differently depending on the glass that it is passing through.
The feat of engineering required to correctly align all of these different light rays is usually achieved by the manufacturer’s use of a lens array. In fact, if you were to pull your lens apart, it wouldn’t be surprising if you found upwards of 16 lens elements all designed to correct for various things along the light’s journey between your lens and your sensor.
Unfortunately, this is also where chromatic aberration tends to rear its ugly head. Hidden within the design of these lens elements are defects – either in the glass or the design of the lens itself – which under specific conditions may cause your photos to exhibit this type of aberration.
I’m not trying to say that you need to have a pro-level lens, in fact, the key point to keep in mind here is that all lenses suffer from chromatic aberration in one form or the other. What matters is whether or not your lens exhibits visible chromatic aberration, and whether in your particular case this is a deal-breaker or not.
Avoiding chromatic aberration defects
Chromatic aberration can actually be effectively removed in post-processing if you are shooting in RAW. However, good practice states that you should try and remove issues in-camera first, rather than creating more work down the line.
The good news is that if you are stuck working with a lens that exhibits some form of visible chromatic aberration there are several easy-to-understand strategies which can help you to remove or minimize the visible effect of it in your photos.
Avoid high contrast scenes
Chromatic aberrations tend to flare up in high contrast scenes. Particularly guilty are shots against white backdrops, landscape shots against a bright sunrise, or, as in the example of this Cheetah, where the light source is behind the subject.
This means that sometimes there’s nothing to do except try and reframe your shot. Swap your backdrop out to something which better matches your subject’s primary color, or wait for more favorable lighting conditions. If you absolutely must capture this shot as-is, then swap over to RAW and get your fingers ready for the possibility that you may need to do some touch-ups in post-production.
Check your focal lengths
Although it’s nice to have access to a wide range of focal lengths, the fact is that most zoom lenses will exhibit various aberrations at the shorter and longest extremes of their focal range. So being able to choose a different focal length will usually help to remove the issue of visible chromatic aberration.
Likewise, using a zoom lens at a wide angle will usually introduce not just chromatic aberrations but various other defects in your image. Instead, consider choosing a prime wide angle lens to handle the job, or, perhaps more practical for your case, make a panorama at a focal length that does not exhibit the chromatic aberration issue and then join the photos in post-production for a flawless result.
Stop down your aperture
Although this will depend on the exact type of lens you are using, stopping down your aperture will usually help to play down the noticeable effects of most lens defects, including chromatic aberrations. Remember that you may need to consider dropping the shutter speed or boosting the ISO to compensate for the light loss if working in a non-studio setting.
If you have access to lighting or flashes, then be sure to experiment with the effect of boosting and adding in extra light.
Reframe your subject to the center of the image
Chromatic aberrations tend to occur more frequently as you move further away from the center of the frame. This is generally as a result of the curvature of the lenses within the barrel. Therefore, being able to reframe your subject closer to the middle may help to reduce, or even completely eliminate, issues with chromatic aberration and other lens-based defects.
This means that you may need to crop your image after shooting to achieve the desired frame, which may be an issue if you absolutely have to maintain every pixel in your photo. If, on the other hand, you are working with small prints, or digital distribution, then the differences between resolutions are not as noticeable until you step down significantly.
So understanding chromatic aberration, how to avoid it, and what you can do about it will help you improve the final quality of your images. If you have any other tips or comments please share them below.