Lens distortion

Lens distortion can either be annoying or great, depending on whether you wanted it there in the first place...

What is lens distortion?

Lens distortion is an optical phenomenon caused by one of the types of lens failure. Lens distortion happens when the camera fails to be rectilinear.

What is rectilinear? Rectilinear, in photography, is the lens’ ability to “preserve” the straight features in buildings, walls, doors, and other objects to appear straight in the picture. Simply put, it keeps straight-looking objects straight, not curved.

Some kinds of lenses such as wide-angle lenses are more likely to distort and stretch images for the sake of capturing all angles. As a result, some straight features that should appear straight in the picture appear distorted and curved. This is basically what lens distortion is.

What are the types of lens distortion?

There are several types of lens distortion. Although the appearance of lens distortion can be irregular and with random shapes. There are at least three kinds of lens distortion that appear most often in photography.

They are barrel distortion, pincushion distortion, and mustache distortion.

1. Barrel distortion

Barrel distortion, also known as negative distortion, is a lens distortion in which the lines protrude outwards at the center, like barrels. Barrel distortion happens when the picture’s center is magnified and the edges are somewhat shrunken.

The phenomenon creates an effect where the lines are curved around, creating a spherical shape that resembles a barrel. Barrel distortion happens most frequently in wide-angle lenses, especially fisheye lenses.

Although wide lenses and zoom lenses are not as “dramatic” as fisheye lenses. They are also prone to creating this barrel-like effect where the middle of the picture is much more magnified than the edges. You may have noticed this type of distortion when shooting architecture or buildings where walls appear to be curved outwards, or minarets appear to be curved or slanted.

Wide-angle lenses are primarily used for architecture photography, and they also tend to produce the most common examples of images with barrel distortion. Interestingly, however, barrel distortion can be easily corrected in post-production. Most editing software, including Adobe Lightroom and Photoshop, comes with lens profile adjustment. To use this feature, you select the correct profile, and the software automatically corrects the lens' distortion.

In most cases, the software will automatically detect the lens you have used to shoot an image and allow you to correct any distortion. So usually, it is just a one-click matter to correct.

Barrel distortion is one of the primary reasons photographers do not shoot portraits with a wide-angle prime or zoom lens. This is because, with a wide-angle lens, you must move closer to your subject to fill the frame. When you do that, you invariably place the subject’s facial features right in the middle of the section where lens distortion starts to happen. You will notice that lens distortion mostly affects the nose, ears, and top of the head.

This is one of the reasons photographers choose slightly longer focal length lenses like 50 to 200mm for portraits. Lenses like these do not reflect the effects of barrel distortion.

2. Pincushion distortion

Pincushion distortion, or positive distortion, is basically the opposite of barrel distortion. Instead of getting the image magnified at the center of the focal length, the lines are hunched inwards and appear smaller in the middle, making edges appear bigger.

This distortion elongates the corners of the image, creating a shape that is similar to how a pincushion looks when you push a pin on it. This distortion occurs more often in zoom telephoto lenses, such as lenses longer than 200mm in focal length. Images shot with these lenses tend to show the reverse effect of barrel distortion, which means straight lines appear curved inside rather than outside.

Again, just like in barrel distortion, in pincushion distortion, straight lines appeared to be affected more than anything else. Therefore, an open roof that is placed at about 1/2 to 1/3 of the frame will tend to have the effects of pincushion distortion more than anything else in the frame. The effects of pincushion distortion are maximum towards the age of the frame. As you move toward the center of the frame, the effects appear negligible.

3. Mustache distortion

Mustache Distortion, also known as complex distortion, combines both barrel distortion and pincushion distortion - creating a wavy image similar to the shape of a mustache. This type of distortion occurs less often than barrel distortion and pincushion distortion, but it is not a rare phenomenon in photography.

In mustache distortion, the barrel distortion magnification appears in the middle of the focal length, and the pincushion distortion gradually takes over around the edges.

This can happen the other way around, where the pincushion happens in the middle and gradually turns to barrel distortion toward the edges. This distortion occurs more in older camera lenses.

What causes lens distortion?

Lens distortion is a distortion caused by camera lenses falling short. Usually, this phenomenon is related to the structure of the lens itself, but the light reaching the camera sensor may also cause lens distortion.

Although lens distortion appears more often in certain lenses, such as wide-angle and fisheye lenses, it is actually more common than you would think. And you should cut yourself some slack because there is no perfect picture, considering that every picture actually has some amount of distortion in it.

Some distortions are visually unnoticeable because they are too subtle to disturb the appearance of the overall image. This can happen when the various parts of the convex-shaped lens have different focal lengths that cause different magnifications.

These differences make some parts of the image appear misshapen, even though every object is focused and sharp. The causes of lens distortion are different depending on the type of lens distortion. For example, barrel distortion often occurs in wide-angle lenses because the view of the lenses is wider than the camera sensor. This is why the center of the image will appear bigger while the edges will appear smaller.

Pincushion distortion happens when the magnification increases with the distance. This is why pincushion distortion occurs more often in zoom telephoto lenses: the further the distance, the bigger the magnification.

Alternate theory to lens distortion

There is an alternate theory in photography that states lens distortion does not happen at all, at least not solely because of the lens we're using. The alternate theory considers that regardless of the focal length of the lens we are using, if we do not move in close to fill in the frame with the subject, then lens distortion will not happen.

Let's say you use a wide-angle lens to shoot a portrait photo. Normally, you would step in close to fill the frame. But what if you do not step in to fill the frame and instead shoot from a distance and crop the image?

Compare such a cropped image with an image shot by a normal portrait lens like 85mm or 135mm. You will notice that the composition appears the same.

Go ahead and try this on your own to see how it works for you. First, capture a portrait image using an 85mm lens or any portrait-length lens. Next, swap the 85mm lens with a standard wide-angle lens without moving or changing the subject's position. A 16 to 35mm or an 18 to 55mm lens would do. Shoot from the same location and crop the composition to match the first image. The two compositions are identical.

Does this mean lens distortion does not happen at all? No, it still happens, not solely because of the lens's optical design but also because of the distance between the lens and the subject. So, if you move in close, lens distortion will be unavoidable, and if you don’t, it can be avoided.

Why is it called lens distortion?

It is called lens distortion because even when other factors may contribute to distortion, the lens is the most probable cause. Unlike perspective distortion, lens distortion is purely an optical phenomenon caused by the shape of the lens itself. To understand this phenomenon further, we also need to learn the difference between lens distortion and perspective distortion.

The position of the camera itself causes perspective distortion. For example, if you photograph a building from a lower angle, its shape may look different from when you take the picture from a straight angle. Perspective distortion can also make more distant objects appear smaller than closer objects.

This type of lens is often used in photography to create optical illusions, such as making objects appear gigantic or very small compared to their actual sizes. The camera’s position and angle create a certain perspective that makes the object appear differently than its actual shape.

On the other hand, lens distortions happen because of the shape of the lens itself, as we have previously discussed. It can happen no matter how you place your camera. Of course, the distortion may appear worst at a certain angle, but even when you just take a picture with a straight eye-level angle, the distortion can still be visible.

Can you fix lens distortion?

There are several methods you can use to fix lens distortion. One of the ways you can do this is by fixing it in the post-production process using photo editing software such as Adobe Lightroom, Photoshop, and Luminar Neo.

This popular editing software allows us to fix lens distortion more simply.

1. Fixing lens distortion in Adobe Lightroom

On Adobe Lightroom, you can choose the Lens Corrections menu and use the automatic profile correction to fix your image. You can click this menu and select the lens you used to take the image. This feature will automatically correct lens distortion and vignetting at the same time.

The automatic profile correction will help you for the most part, and you just have to take some further steps to get the desired result. But sometimes, the automatic profile correction cannot help, especially in severe distortion cases, so you must fix it manually on the Transform Tab. The Transform Tab also has an automatic setting. You can try it to see if it helps, but if it does not, you can still use the menus provided below:

Vertical

You can use this menu to correct vertical distortion on the image.

Level

You can use this menu to level the horizontal features of the image.

Auto

The auto menu balances and corrects both vertical and horizontal distortion. It also helps balance your picture without having to crop some parts of it.

Guided

This menu will help you a lot when you correct the distorted image manually. The guide menu will provide you with lines you can use as a guide. Following these guidelines, you can easily see the part of the image that is still distorted and needs fixing.

Full

The full menu has a function similar to that of the auto menu. It will balance out the overall image. The full menu can be used in extreme distortion occurrence, but some parts of the image might be cropped.

Most of the menus mentioned will help you get through most distortion cases. However, in very severe cases, you may still need to take extra steps to fix some parts of the image that appear curved. You can use the transform slider to fix both vertical and horizontal lines manually.

2. Fixing lens distortion in Photoshop

You can fix the lens distortion on the Custom menu. Some features of Photoshop can also be used to fix lens distortion.

Grid

This feature will provide you with a grid that you can use as a guide. By turning on the grid, you can easily see the curved and distorted part of the image.

Straighten tool

This tool is very helpful in straightening the curved lines. Use the slider in the transform tab to adjust the vertical and horizontal perspective, following the grid as a guide.

Remove distortion slider

This tool will help you correct barrel and pincushion distortion more easily in one single step. Note that the more adjustments you make, the more likely you will need to crop more parts of the image. Keep this in mind every time you take a picture so that when you encounter some objects such as buildings. You know you will need to do some lens distortion correction later; you can make sure you leave enough space for cropping.

Both Lightroom and Photoshop are excellent tools for removing lens distortion. You can use one or even combine both of them. However, sometimes, removing some kinds of lens failures in the post-production process does not always give you the best result.

How to prevent lens distortion?

One of the things you can do is prevent lens distortion altogether during the production process. There are some ways you can do to prevent lens distortion below:

1. Avoid using extreme wide-angle lenses

Wide-angle lenses always create distortion. That is what you can expect because they basically squeeze a wider view into one single frame. So, lens distortion is normal when you use this kind of lens, especially the ‘extreme’ ones, such as the fisheye lens.

Instead of forcing the camera to fit a wider view into a single frame, maybe you can consider taking some steps back and taking the picture from a distance to get a wider view.

2. Keep some distance between you and the subject

When you take a picture too close to the object, the chance of lens distortion occurring is even greater. It may also create a perspective distortion and give you another problem to deal with in post-production. This is why you must keep a distance between yourself and the object you want to photograph.

3. Pay attention to the composition and add some space

It is particularly important to add some space around the object. This step will help you a lot in post-production. First of all, by adding some space around your object, the object itself could be safe from distortion, and only the edges, which is the extra space that is being distorted. The extra space is also extremely useful in post-production work, just in case you need to do some cropping.

4. Choose lenses with less distortion

Most lenses nowadays are already pretty good at avoiding distortion occurrence. Older lenses, however, tend to create more distortion. So, select your lenses carefully before you take some pictures. Many photographers recommend using 50mm lenses to avoid lens distortion.

This lens is also known for not having optical distortion issues. Lens distortion can be annoying if you do not expect it, but sometimes, it does not have to be bad. Some photographers intentionally distort lenses to create a certain perspective or an optical illusion in their images. You, too, can use lens distortion creatively and experiment with different types of photos.