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Chromatic aberration

Beyond the spectrum - decoding chromatic aberration...

What is chromatic aberration in photography?

Chromatic aberration is also known as spherochromatism, or chromatic distortion. It is basically when the camera’s lens fails to focus all colors onto the same point, which results in a line of unwanted colors around the edges of an object in a photograph.

Have you ever taken a picture, expecting it to come out well, only to end up with colorful light distortions around your object? Or even a halo light? You may wonder, “What are these lines, and how did I capture them?” Well, those light lines are what we call chromatic aberration.

While arguably interesting looking, these distortions can be disruptive because they make pictures appear blurred and have low infidelity. Unfortunately, chromatic aberration is pretty common in photography.

Most photographers have experienced their shots ruined by chromatic aberration, but even fewer actually understand what it is, why it happens, and how to avoid it. In photography, chromatic aberration is also often called “color fringing” or “purple fringing” because the color purple often appears in a chromatic aberration.

However, not all purple fringing can be attributed to chromatic aberration. There are two types of chromatic aberration: axial (longitudinal) and transverse (lateral).

1. Axial aberration

Axial aberration is a focus shift where the different wavelengths of light are focused at different distances from the lens.

In the focal plane, longitudinal (axial) chromatic aberration can appear around objects throughout the image from the center to the focal plane because of the magnification or distortion of the lens corners. It usually appears as lines in red, green, blue, or combinations of all those colors.

Stopping down the lenses can reduce it. This chromatic aberration is more prominent in fast-aperture lenses than in slower ones.

2. Transverse aberration

Transverse aberration happens when different wavelengths are focused in different positions.

Transverse chromatic aberration usually only appears in the image's corners and the high-contrast areas. Unlike longitudinal (axial) chromatic aberration, transverse chromatic aberration never shows up in the center of the image.

It appears more in low-quality lenses, fisheyes, and wide-angle lenses. It cannot be reduced by stopping down the lenses. You need to fix it in the post-production process.

The two types of chromatic aberration may occur simultaneously, even though they have different characteristics. This is because most lenses can have longitudinal and lateral chromatic aberration problems.

If you get both chromatic aberrations, you will need to do extra work to reduce them. You can stop down the lenses first to reduce the longitudinal chromatic aberration and then get rid of the lateral chromatic aberration later in the post-production process. Chromatic aberration often appears in thin, colorful lines along the edges of objects where high contrast of dark and light colors appears.

Purple or magenta are the colors that appear the most in a chromatic aberration, but other colors, such as green, yellow, blue, and red, also occur sometimes.

Another form of chromatic aberration is a form of halo around the object. It can be a colorful or light halo with no vivid color.

Why does chromatic aberration occur?

Chromatic aberration happens when the different wavelengths of light are refracted at different angles through the lens.

This makes the colors hit the lens on the different focal planes on the camera lens, resulting in a color fringe appearance. Let’s go back to fundamental physics: white light combines all colors in the color spectrum. Each of these colors has different wavelengths, focusing at a slightly different distance.

These different wavelengths can cause some complications for your lens since different colors reach the camera at different times. For example, blue light is able to pass through lenses faster than red light.

This has to do with the refractive index of the lenses, which affects the focus of the camera, which is a primary factor in the occurrence of chromatic aberration.

The camera lens acts as a prism that refracts all of these colors. Most lenses can focus all colors simultaneously, but sometimes, there can be strong transitions from bright to dark around the object's edges.

When this happens, the camera lens may find it challenging to focus on all the colors, resulting in chromatic aberration. While this problem is common enough, higher-quality lenses are less prone to chromatic aberration than lower-quality ones. In this particular case, investing in a pricier lens can cut down a photographer’s chromatic aberration problems to some extent.

But still— in reality, each color reaches the lens at a different speed and slightly different time, making any lenses not perfectly safe from chromatic aberration. In other words, it is impossible to find a lens that is perfectly immune to chromatic aberration because it is a physiological problem of all lenses when exposed to light.

In the world of photography, there’s something called the “circle of least confusion.” It is the ideal condition for a lens to focus all the wavelengths at the same point so the chromatic aberration occurrence can be minimized.

If you can achieve the conditions of the “circle of least confusion,” you may nail your shot without any colorful light distortions.

Is chromatic aberration normal?

Yes, chromatic aberration is normal and common in photography. As we mentioned, no lens is expensive enough to be immune to this problem.

Chromatic aberration is so common that even professionals with years of experience in their pockets may still have to deal with the problem. The good news? Well, since it is so common, you don’t have to worry so much if you happen to take a photo with chromatic aberration.

It happens (a lot). It’s just a matter of physics and the nature of the camera lens. Of course, in an ideal situation, we want a picture without chromatic aberration or lens flare. We cannot control the nature of lights, so it can still happen. But there are ways to minimize it.

Is chromatic aberration bad?

Whether chromatic aberration is bad or not is down to personal preference. Some people see it as an annoying problem, while others accept it as part of the art of photography.

From another perspective, chromatic aberration doesn’t always make a picture appear bad. On the contrary, sometimes, it added different nuances to the picture. Having the rainbow-color spectrum lining the object of your picture can look somewhat surrealistic and psychedelic and even add a dream-like effect. In summary, it can be favorable.

As evidence that chromatic aberration doesn’t have to be a problem, we just need to point out that some photographers even choose to add this effect to their photos afterward purposely. In recent years, chromatic aberration has gained popularity and appears frequently in photographs, moving pictures, and video games.

Like anything in art, some people hate the chromatic aberration trend, and some like it enough to experiment with it. After all, it does make a picture appear somewhat more ‘raw’ and unique.

If you are one of the photographers who enjoy this effect, you can experiment and add a chromatic aberration filter to your pictures. You can also add the color fringe by separating the red, green, and blue channels in editing software.

Of course, this doesn’t work on all photographs. If you seek a clear and sharp picture—say, for a museum catalog where every detail of the object must be high-fidelity—then chromatic aberration is definitely a problem.

Worry not because the sections after this will tell you how to eliminate it.

How to fix chromatic aberration?

As mentioned earlier, chromatic aberration can affect all lenses, even high-quality ones.

Some lens manufacturers work hard to minimize chromatic aberration and other forms of distortions using various mixes of elements, such as Short-wavelength Refractive Glass.

However, chromatic aberration can still appear in the photographs. Thankfully, it can be altered in the post-production process. You can remove it on various photo editing software such as Adobe Photoshop or Lightroom.

1. Lens correction panel

Whether using Adobe Photoshop or Lightroom, you can remove the chromatic aberration in the Lens Correction panels. It will automatically remove the color fringes that appear on your pictures. You can also use the defringe slider to refine the color fringes further.

2. Masks and blending modes

For a stubborn chromatic aberration occurrence, you need to put more effort into removing it. You can use masks and blending modes to remove blunt fringes.

The first way you can do this is by using the blur effect just a little bit to disguise the fringes. Use the blending mode to set the picture back to normal. The chromatic aberration will be gone or appear less saturated. This method will make your picture look less saturated. You can fix this by using the masking layer and selectively removing the color fringing.

3. Brush

Lastly, you can use the brush and paint a soft white brush to reveal the color blending mode layer beneath. If you follow those steps carefully, you may eliminate the chromatic aberration. But keep in mind that sometimes the fringes appear too harsh and may still appear subtly in the picture.

How to avoid chromatic aberration?

Even though chromatic aberration is something that we cannot avoid altogether, there are some things we can do to fix it. Here are some ways you can fix chromatic aberration:

1. Avoid shooting in high-contrast scenes

This is actually a no-brainer because chromatic aberration often appears in high-contrast scenes. If you shoot in daylight, you can wait until the sun sets lower so the light is less bright. This way, the light may appear softer, making the scene look less contrasting.

2. Center the subject in the middle of the frame

You can do this to avoid transverse chromatic aberration. You can fix the composition later by cropping the image. If you want to do this, take the picture in high resolution so the picture quality is still good even though you crop it.

3. Avoid using the shortest and longest focal length

When you use zoom lenses, avoid using them in either the longest or shortest focal length. The longest and shortest focal lengths are more prone to chromatic aberration.

4. Change your color image to black and white

The Black and white image is not free from chromatic aberration. But if you take your picture in black and white, the saturation of the chromatic aberration will be disguised.

5. Use lenses made of low-dispersion glasses

This one is more technical, and you need to understand lenses to pick the one made from low-dispersion glasses. The ones that contain fluorite can significantly reduce chromatic aberration.

6. Close down your aperture

You can avoid longitudinal chromatic aberration by closing down the aperture. It will decrease the amount of light that reaches your lens, and you must compensate by decreasing your shutter speed and adjusting the ISO to get the proper exposure you desire.

7. Use an achromatic lens

Photographers often use achromatic lenses to avoid chromatic aberration.

These lenses bring two-wavelengths (usually red and blue) to help these two colors focus on the same plane. Achromatic lenses often feature two individual lenses with two different amounts of dispersion. One of these two lenses is usually made out of ultra-low dispersion glass.

8. Use in-camera solutions

Some cameras have an in-camera setting that can decrease transverse aberration. This feature is designed specifically to reduce purple fringing.

9. Fix it in the post-production process

Lastly, when you have already completed all of these steps but still experience chromatic aberration, you can fix it in the post-production process explained in the previous part above.

Sometimes, chromatic aberration appears so subtle that we cannot see it unless we zoom in on the picture and look very closely.

In high-quality pictures taken using high-quality lenses, sometimes the fringes appear even more slightly only people with really keen eyes can see. We can prevent chromatic aberration using high-quality lenses, avoid wide-angle lenses, and shoot with a narrow aperture.

If you experience chromatic aberration, the best way you can is to reduce it during the shooting process. Either by adjusting your camera settings, changing lenses, or doing other technical work you can do.

You don’t have to put so much effort later in the post-production process by reducing it during the production, especially with a harsh chromatic aberration process that cannot always be removed completely from the picture.

If you see chromatic aberration as a form of unique art in photography, you can leave it as is and even enhance chromatic aberration more. But if a clean and sharp picture is your goal, then correcting the chromatic aberration is a way you can improve the image quality of your photograph.

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