What is lens distortion?

Question: I’ve noticed that straight lines in my images appear to bend. Is this because of distortion? And if it is, what can I do about this problem?

Answer: There are two main types of distortion. The first is perspective distortion, where a distant object appears smaller than a closer object. This is commonly seen in architectural photography, where buildings appear to lean inwards when shot from ground-level. Perspective distortion can be corrected by using a tilt & shift lens, or with distortion correction software such as DxO’s Viewpoint 2.

The effect is most severe at wider focal lengths, and occurs irrespective of optical quality. The other type of distortion is optical distortion, which is reliant on the quality and design of the glass. It occurs because the shape and arrangement of the elements cause straight lines that run near to the edge of the frame to appear bent. Focal length has a huge impact on optical distortion, with wide-angle lenses producing barrel distortion (where straight lines bend outwards towards the edge) and telephoto lenses producing pincushion distortion (where straight lines bend inwards towards the centre). 

Avoid distortion effects
The easiest way to avoid lens distortion is simply to correct it afterwards in editing software. Lightroom, for example, has lens correction profiles built-in, which do the job in a single click. You can also adjust manually. Some cameras have lens correction built-in, though this is only applied to JPEGs and not RAWs. As a general rule, the more expensive the lens, the less lens distortion you’ll get. Finally, at 50mm there’s hardly any distortion on any lens, so if possible shoot at this focal length by adjusting your position.

Three ways to remove unwanted distortion...

1. Photoshop
Open a RAW file into the Adobe Camera Raw window. Simply click the Lens Corrections icon, select the Profile tab, and check Enable Lens Profile Corrections. This automatically applies the profile for your lens. For JPEGs, go to Filter>Lens Correction . Again, Photoshop will apply the  lens profile.

2. Elements
Open your image in Elements, and if it’s a RAW file, make any basic tweaks in the Camera Raw window before clicking OK. Go to Filter>Correct Camera Distortion. Unlike in Photoshop and Lightroom, this won’t automatically apply lens profiles for your particular make and model, so adjustments must be done manually. This is very straightforward – just tweak the Remove Distortion slider.

3. Lightroom
Import your image in Lightroom, then press D on your keyboard to enter the Develop module. On the right of the screen, scroll down through the control panels until you reach Lens Corrections. Click the Profile tab, and check the Enable Profile Corrections box. This will automatically select the right lens profile. If not, you can always adjust it manually using the  Distortion slider.