Have you ever wondered what are those coloured streaks around the edges in your photos?
That’s chromatic aberration, a common nuisance in optics, including photography where the light travels through series of lenses before it hits the sensor to produce an image.
In this article, I will explain what chromatic aberration is, what you can do to avoid it, and how you can fix it in post-processing.
What is Chromatic Aberration?
Chromatic Aberration (CA) is an unwanted optical effect that occurs when a lens doesn’t refract all the wavelengths of light into the same point.
Different wavelengths (=colours) travel at different speeds through the glass of a lens, resulting in light dispersion. This effect becomes the most noticeable in high-contrast settings, where it significantly blurs images and causes coloured edges.
A theoretical, perfect lens would be able to focus all colours into one focal point, as shown in the image below:
For now, this is impossible, so we have to deal with two types of CA – Longitudinal (Axial) Chromatic Aberration and Transverse (Lateral) Chromatic Aberration.
Longitudinal (Axial) Chromatic Aberration
Longitudinal chromatic aberration (LoCA), also called bokeh fringing, occurs when different wavelengths that pass through the lens are focused at different distances from the lens (focus shift), as shown below:
Longitudinal chromatic aberration leads to colour fringing around subjects throughout the entire image, in the centre as well as on the edges.
While long focal lengths and fast prime lenses are more likely to produce LoCA, stopping down the aperture helps reduce LoCA as it increases the depth of field so that the all the wavelengths are still in acceptable focus.
Lateral (Transverse) Chromatic Aberration
Lateral chromatic aberration, also known as transverse chromatic aberration (TCA), occurs when different wavelengths are projected to different points in the focal plane.
TCA is typical for short focal lengths, and unlike with LoCA, stopping down the lens won’t help. Furthermore, TCA won’t appear at the centre of the frame but becomes significantly more noticeable towards the edges of the frame, especially in high-contrast areas.
TCA can be quite easily removed or reduced with post-processing software, such as Lightroom.
How to Avoid Chromatic Aberration
I’ve explained what chromatic aberration is, what causes it, and what it looks like. At this point, you might think, “great! Another problem to worry about”, but let me put your mind at ease.
I’ll show you how to minimize CA to the point where it won’t be a problem.
1. Shoot in RAW
Shooting in RAW has a lot of advantages, and if you’re seriously into photography, you should already be doing it. RAW images are crucial when you intend to post-process them in software, such as Adobe Lightroom or Luminar 4; uncoincidentally this is how you’re going to remove CA.
The easiest way to get rid off CA is to import an image into Lightroom, navigate to Develop module, open Camera Correction panel and check Remove Chromatic Aberration. Lightroom will automatically analyse your image and remove CA.
2. Pay attention to focal length
More often than not, zoom lenses are more affected by chromatic aberration than prime lenses, especially at their minimal and maximal focal lengths.
For example, if you own an 18-200mm lens avoiding both 18mm and 200mm will guarantee the best results. If you’re all about image quality, you might want to consider using prime lenses instead of zoom lenses; and while you’re at that, expect to spend quite some money to get a high-quality lens that will create images with the least amount of CA.
3. Avoid high-contrast scenes
Don’t take this advice too literally; it’s completely fine to photograph contrasty scenery, but be mindful of difficulties it brings. Firstly, CA is the most noticeable in high-contrast situations; secondly, shooting during the low-contrast times of the day, such as the golden hour, usually produces better and more eye-pleasing results.
4. Stop down the lens
You can experiment with your lens to figure out which aperture value gives the best quality image, but as a rule of thumb you should stop down by at least one or two stops from the widest aperture of your lens to avoid chromatic aberration.
As you stop down the lens, you will lose shallow depth of field; additionally, you’ll also have to use slower shutter speed and higher ISO setting to make up for the loss of light and avoid unsharp images.
5. Move the main subject away from edges
As I mentioned earlier, you can avoid LoCA by stopping down the lens, but how do you avoid the TCA?
TCA is the most noticeable towards the edges and virtually disappears in the middle of the frame. To take the full advantage of this knowledge, you should position your main subject towards the centre of the frame, where there’s the least chromatic aberration.
How to Fix Chromatic Aberration in Lightroom
You won’t be able to always avoid chromatic aberration in your photos; more often than not, you will have to remove it with post-processing software. Although there are several good ones out there, I recommend Lightroom for chromatic aberration removal. Its tool is as simple as it gets – you just need to click on a checkbox.
Import your photo into the Lightroom, navigate to the Develop module, opens the Lens Corrections panel and tick the Remove Chromatic Aberration checkbox. That’s all.
In some rare cases, Lightroom won’t do a great job removing CA from your photo and you’ll have to make use of its Manual tool for the removal. It takes some practise to get right and I won’t go into detail in this blog post, but here’s a video by Scott Kelby where he explains the process.
While we wait for camera companies to perfect the lens glass, we’ll have to deal with chromatic aberration. In most cases, it’s not that big of a deal, especially considering how easily we can remove it in post-process.
Did you know what chromatic aberration was and what caused it? Let me know in the comments.