Distortion in photography

It’s been a while since I last wrote about the basics of photography. I had already started covering many of the key terms worth knowing when you first get into photography. By the way, a summary of all the photography terminology is available, even though it could probably still be expanded. This article goes back to the basics and explains distortion in photography.

This is probably one of the best-known terms among beginners, and not only beginners. In future articles, I’ll also cover other optical flaws such as chromatic aberration, diffraction, coma, and more.

You don’t need to know every photography term by heart, or understand every single one in detail. Still, I think learning this vocabulary is an important step if you want to deepen your photography skills. Whether you’re buying a new lens to explore a different type of photography, or you’re starting to process RAW files in post-processing software, understanding distortion is, in my opinion, not just useful but almost essential.

So, I’m starting this “not too technical” article with the aim of sharing what I know in a simple, practical way. That said, even though lenses can suffer from this phenomenon, more and more software can correct it very effectively during post-processing. This can sometimes lead to a slight loss around the edges of the image, as the software has to compensate for the distortion, as is the case with my Tamron 20mm f/2.8. In general, distortion should not be the deciding factor when choosing a lens. That said, it really depends on the type of photography you do…

To define distortion simply, I would say it is a deformation that affects an image as a whole, along with the elements within it. We might naturally assume that every part of an image is reproduced with the same magnification, regardless of where it appears in the frame. In reality, that is not the case. Depending on the lens used, the same element captured in different parts of the image may not keep exactly the same shape. Distortion is therefore a geometric aberration, linked only to the lens, that affects how subjects appear within the image. The whole image is distorted, with the degree of distortion varying depending on where each element is located in the frame.

Distortion occurs when light rays enter, pass through a set of lens elements, and then exit the lens. The rays do not all pass through the same part of the lens. Those closest to the optical axis are only slightly affected, while rays passing farther toward the edges are affected more strongly. This is why distortion is often more visible around the edges of an image. A perfect lens, in terms of distortion, would allow all light rays to be transmitted without altering the geometry of the scene. Some brands, such as Laowa, even produce lenses marketed as “zero-distortion,” offering almost no distortion on ultra-wide-angle lenses, such as the Laowa 12mm f/2.8 ZERO-D. Manufacturers have also developed technologies to control distortion, including the use of aspherical lens elements, which help light rays converge more accurately toward a single focal point.

Distortion is measured as a percentage and represents the difference between the ideal position of an object in the image and its actual position. Depending on the type of distortion, this percentage can be positive, for pincushion distortion, or negative, for barrel distortion.

Before buying a lens, it is worth checking its distortion percentage and the type of distortion it produces. You can look at DXOMark, or any other website that provides this kind of optical analysis. This allows you to check, for both zoom lenses and prime lenses, what type of distortion is present and how it behaves as you move away from the center of the image.

To give you an example with my Tamron 20mm f/2.8, it has very strong barrel distortion. This tends to make subjects in the center of the image stand out clearly, while distorting elements much more around the edges. Tests show around 8% barrel distortion, which is still very high for a wide-angle lens, even if it can be corrected quite well with DXO or Lightroom.

• Barrel distortion: this is characterized by an image that appears “inflated” in the center, like a barrel, hence the name, while the edges of the image tend to curve inward. The magnification of elements in the image therefore decreases toward the edges. This defect is especially visible on horizontal lines, particularly near the top or bottom of the frame.

This type of distortion is mostly found on wide-angle lenses, but also quite often at the shorter focal lengths of zoom lenses, such as a 16-35mm. Because this type of lens has such a wide field of view, the image has to be projected in a way that can create visible curvature.

Here is a rather striking example of this type of defect with my Tamron 20mm f/2.8 lens, which shows strong barrel distortion. DXO corrections can compensate for this type of flaw fairly well.

• Pincushion distortion: this is essentially the opposite of barrel distortion. One of its main characteristics is that straight lines tend to curve outward from the center of the image toward the edges of the frame. It is very common on zoom lenses, especially at the longest focal lengths, and on telephoto lenses. High-end telephoto lenses now control this optical flaw increasingly well, with only negligible pincushion distortion, and any remaining distortion can usually be corrected easily in post-processing.

Here is an example of fairly strong pincushion distortion from my Tamron 70-180mm at 180mm. The pincushion distortion is measured at more than 3.5% at 180mm, which is honestly quite a lot. Fortunately, software such as DXO handles this kind of lens imperfection beautifully, so it can be corrected quite easily.

• Mustache distortion: this is the last of the three types, and the most complicated to manage in post-processing. It can be seen as a combination of the two distortions mentioned above, barrel and pincushion. Straight lines appear to curve inward toward the center of the image, then outward again as you move toward the edges and corners. This type of distortion is mostly found on older lenses, or on very short focal lengths, even on some recent lenses such as the Samyang 14mm f/2.8.

A few words to summarize these points. Because of their larger size, full-frame sensors (24x36mm) are more exposed to distortion phenomena. When you mount a lens on a full-frame sensor, you use the whole image circle produced by the lens, while with an APS-C sensor, which is about 1.5 times smaller, you only “use the center.” If you mount a full-frame lens on an APS-C body, you will therefore see fewer optical flaws. However, lenses designed specifically for APS-C generally show distortion similar to their full-frame equivalents. For example, a 16mm APS-C lens on an APS-C body will have almost the same distortion as a 24mm full-frame lens on a full-frame body. Here is an article for you to know everything there is to know about sensor size in photography and how it affects your images! Regarding lenses:

• Fish-eye lenses: very strong barrel distortion, although on this type of lens, it is an intentional effect,
• wide-angle lenses: mostly barrel distortion, but with a small caveat. On a prime lens like my Tamron 20mm, and also on zoom lenses, this type of distortion can be found. Because the image curves outward, the lens can actually frame wider than a true 20mm. DXOMark shows this clearly with a 20mm prime lens, such as the Sigma 20mm f/1.4 DG HSM Art, which frames wider at the edge of the image. This also means that if you crop the edges or want to “keep the proportions” during post-processing, you will not necessarily lose any image compared with the advertised 20mm focal length.

• Standard focal lengths: it all depends on the lens, but barrel distortion is generally less pronounced. Note that on zoom lenses such as 24-70mm or 16-35mm, we often find barrel distortion at the shortest focal lengths, as with wide-angle lenses, and pincushion distortion at the longest focal lengths. Here is an example with the Canon 24-70mm f/2.8 II L USM.

• Telephoto lenses: they mostly suffer from more or less pronounced pincushion distortion, depending on the lens’s quality and range. On zoom lenses with very wide focal ranges, such as 18-300mm, pincushion distortion at the long end will often be quite significant.

We have just looked at the three main types of distortion in photography. These are linked to lens construction. However, there are other types of distortion, or rather perspective deformation, related to how you shoot and to the distance between the camera and the subject. There are mainly two types.

This is a classic type of distortion that appears when shooting a subject at very close range. It does not come from an optical flaw in the lens, but from the fact that you are very close to your subject with a very short focal length, typically a wide-angle lens, often the only type of lens that allows you to get that close. This is the case, for example, if you try to shoot someone’s portrait with a wide-angle lens such as an 11mm on APS-C or a 16mm on full frame. The eyes, nose, and other facial features will be completely distorted and will appear much larger.

A quick clarification: we often tend to think that short focal lengths distort perspective more than long ones, such as telephoto lenses, but that is actually false. All lenses have and offer the same perspective. It is simply the distance between your camera/lens and the subject that changes the perspective.

You can, however, use this type of stretch distortion to emphasize part of a subject by getting very close to that area. It will draw attention to it and make it appear much larger in the image than it actually is.

Unlike extension distortion, compression distortion appears when using telephoto lenses. With a long focal length, the perspective appears compressed, and background elements, sometimes miles apart, can seem much wider and larger than they actually are.

It’s not that hard to correct distortion. If you shoot JPEG, I recommend enabling your camera’s optical corrections. Generally speaking, they will correct these flaws quite well, even though some artifacts may remain. If you shoot RAW, you simply need to enable the correction profile for the lens, or for the camera and lens combination, to correct image distortion. And that’s about it. By the way, I have written a comprehensive article explaining the differences between RAW and JPEG.

I’m coming to the end of this article on distortion in photography. I hope you found it useful and now understand why it is worth knowing about this kind of optical flaw.

I’ll be back soon with a new article on optical defects!

Written by Sylvain PONS

I've been passionate about photography since 2010, learning as I went along. Today, I dedicate myself to guiding others in their choice of camera gear and sharing a variety of tips to improve their photography skills.

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