Many of Canon’s latest cameras and lenses now support focus breathing correction. But what is focus breathing in the first place and why would you want to correct it? Read on to find out.

 

What is focus breathing?

Focus breathing refers to the change in the angle of view that occurs when the focus position changes. For example, take a look at the video below.

Focus breathing correction: Off

Pay attention to the background. Do you notice that it seems to “zoom out” when the focus moves away from the bicycle, and “zoom in” when the focus shifts back to the bicycle?

The expansion and contraction of the angle of view resemble “breathing”, hence, the term “focus breathing”.

 

Why does focus breathing happen?

Focus breathing happens because the focusing elements inside a lens need to realign to focus whenever the focus position changes. This movement can change the actual angle of view slightly.

The change can be obvious or subtle, depending on the lens. However, generally, it tends to be more obvious at shorter focusing distances and on superzoom lenses (lenses that cover a large focal range).

The focusing element in the RF135mm f/1.8L IS USM. The layout and number of focusing lens elements between lens models.

 

Why is focus breathing an issue?

Focus breathing occurs whenever a lens focuses during both still photography and video capture. However, it is particularly obvious in video because focus position transitions are captured.

Such transitions are frequently deliberately employed as a storytelling technique. They also occur when the autofocus system tracks a moving subject. Given the frequency of focus transitions throughout an entire project, you can imagine how often focus breathing occurs—and how distracting it can be!

It’s one of those things that may not be noticeable to the casual, untrained observer but is hard to “unsee” once you have noticed it. It makes the finished work look choppy and unprofessional.

 

Focus breathing correction: The digital correction of focus breathing

Cinema lenses are designed to minimise focus breathing. This is no surprise considering how important this is to video and filmmaking. All the effort poured into minimising focus breathing is also one reason why they are so expensive!

However, as more people shoot video with photography lenses on their photography/hybrid cameras, it has become more important to address focus breathing on still photography gear too.

Canon’s solution to this is focus breathing correction. This uses optical design information from Canon’s database to calculate and digitally correct focus breathing for each compatible lens.

Here’s a clip of the same scene as the one above, shot with focus breathing correction enabled. Do you notice the difference?

Focus breathing correction: On

 

Things to know when using focus breathing correction

1. Compatible cameras and lenses
Both your camera and lens must be compatible with focus breathing correction for you to use the function. For the most updated list of compatible gear, see:

Lenses compatible with Focus Breathing Correction in Movie Recording

2. You must enable the function first

On the lens we used (RF24-50mm f/4.5-6.3 IS STM), “Distortion correction” is unavailable by default. However, you might have to enable distortion correction first on certain lenses, such as the RF24-70mm f/2.8L IS USM.

3. Frame the shot a little wider
There may be slight cropping, although this depends on the shooting conditions.

4. Know this if your lens has a focus limiting switch
Corrections on lenses with a focus limiting switch are performed according to the focusing range set on the switch. Results may not be as desired if you shift the focus beyond this range.