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You recently discovered an exciting camera you’d like to get. So you head out to buy it so you can immediately put it to use.
After a few shots, you check your computer to take a look at the photos and what you see makes your enthusiasm drop.
First off, the straight lines appear bent or curved. Then, the edges seem to lose clarity and look dull.
What you just experience is known as lens distortion. And it’s a critical aspect of photography because without having a full understanding of it, it can stagnate your growth in photography.
What is Lens Distortion?
In summary, lens distortion is when a lens produces curved or bent lines in the wrong places. That is, where you’re meant to have a straight line, the lens delivers a curved one.
In photography, there are two types of lens distortion:
- optical distortion
- and perspective distortion.
In this article, we’ll take a deep dive into each so you’ll be able to differentiate them. We’ll also provide you with simple ways to drastically reduce the effects of distortion.
And to wrap it up, we’ll go over two kinds of optically designed lenses: rectilinear lens and curvilinear lens.
But first, to help you gain a deeper understanding of distortions, we’ll unravel how lenses work
How does a lens work
Glass lenses allow us to capture a sizable field of view by bending light. By doing this, it projects an image on a camera sensor or film.
The wider the field of view that needs to be captured, the more extreme the curve of the glass will be.
Looking at types of lenses, wide – angle lenses are more spherical than telephoto lenses.
This curved nature equips the lens with the ability to capture wider views of a scene.
However, this curve created by both lenses has another effect. Which is, the distance of objects at the edge of an image to the lens is different from the distance of those from the centre of the image to the lens.
This mismatch results in curved or bent lines which distort the image.
Types of Lens Distortion: A breakdown
As we discussed earlier, there are two main types of distortions: Optical distortion and Perspective distortion.
So, let’s cover each one.
1. Optical Distortion
An optical distortion is as result of a lens error. What this means is that certain optical elements that are used to reduce visual deformation end up distorting an image.
These optical designs cause straight lines to appear curvy or bent in images.
Almost all lenses are plagued with optical distortion. Higher grade of lenses means you’ll experience less optical distortions.
There are three major types of optical distortion;
- Barrel Distortion
- Pincushion Distortion
- Mustache Distortion.
Barrel Distortion
In a nutshell, this occurs when straight lines bend inwards from the centre of the image.(like the walls of a barrel).
This is very common among wide angle lenses like a 22mm lens or a Nikon 22 – 70mm for example. Because they possess a wide field of view, they tend to be wider than the size of the image sensor.
This causes the straight lines to bend inwards making the image appear “squeezed in”
How to fix it
You can reduce the effects of barrel distortion by simply adding compensating optical elements. However, it’s important to note that these elements will increase the size and weight of the lens.
Another way to trim down the level of barrel distortion in images is to wait till the post processing so you can use certain softwares like photoshop and lightroom.
On photoshop for example, simply head over to the filter section and click “lens corrections”. You’ll notice an option to auto correct. Select that and your image will be transformed.
Pincushion Distortion
This produces the opposite effect from barrel distortion.
Rather than the image curving in, pincushion distortion causes the straight lines to curve outwards from the image centre.
It is common amongst telephoto lenses because they increase the magnification of images towards the end of a frame.
In this case, the field of view is smaller than the size of the sensor. So, to allow the image to fit in, it has to be stretched.
How to fix it
The entire process is similar to the Barrel distortion. You’ll need to add certain optical elements to compensate for the distortion.
Also, post processing softwares like lightroom and photoshop will be very effective
Mustache Distortion
This is commonly referred to as a complex distortion and rightfully so. It’s a combination of a barrel and pincushion distortion.
Both happen at the same time and on the same image. This distortion is characterized by straight lines appearing curved inwards towards the centre of the frame, and curved outwards at the corners.
How to fix it
Unlike the previous distortions that require a straightforward process, you’ll need a specialised software to fix a mustache distortion
Photoshop and lightroom are ineffective in handling this distortion and causes it to appear worse. For example, trying to fix the barrel side of the distortion will make the corners of the image curve even more.
So, you’ll need to get your hands on a specialised software if you’re battling with a moustache distortion.
2. Perspective Distortion
This is the second type of distortion found in photography. And unlike optical distortion, it has nothing to do with the camera lens.
This type is caused by the position of your camera in relation to the subject you’re trying to shoot. Or how the subject is positioned in an image.
With this definition, there are two types of perspective distortion that can arise from this;
- Wide angle or extension distortion
- and telephoto or compression distortion.
Let’s take a look at each:
Wide angle or Extension Distortion
This distortion applies to only wide angle lenses.
Ever notice how if you hold any object in your hand and draw it closer to your eye, it appears larger than other objects in the background?
Well, photography shares this same experience. When you position your camera close to a subject, the part closest to the lens, will appear larger than others.
This creates a disproportionate image where the background and the images look smaller than the subject closest to the camera lens.
Telephoto or Compression Distortion
This is the opposite of an extension distortion and is only possible with a telephoto lens.
To achieve this distortion, the photographer will have to stand far away from objects causing them to be larger than normal.
Optically designed lenses: Rectilinear vs. Curvilinear
There are lenses that are designed to produce certain optical effects on images.
Rectilinear lenses otherwise known as “human eye” lenses are made to produce straight lines with zero curves or bends. With this function, they can stretch objects so they appear straight.
Curvilinear lenses are the direct opposite. They distort images by making straight lines appear curved. Hence why they’re referred to as “fish eye” lenses.