Focus Breathing
A lens's apparent field of view subtly widening or narrowing purely from racking focus, with the focal length ring untouched — an optical side effect of how some lens designs shift internal elements to focus, not a deliberate zoom.
Invisible in a single still photograph, since only one focus point ever gets captured. It becomes a real, distracting problem specifically during a video focus pull between two subjects at different distances. See the focus breathing answer page for which lens types minimize it and why.
Frequently Asked Questions
Is focus breathing a defect, or does every lens have some?
Nearly every lens breathes to some degree — it's a byproduct of how internal elements move to focus, not a manufacturing flaw. Dedicated cinema lenses and some newer stills lenses are specifically engineered to minimize it well below what a typical photo lens shows.
Can focus breathing be corrected after filming?
Some newer mirrorless bodies apply digital correction in-camera or in editing software for specific supported lenses, digitally compensating the framing shift, but this depends entirely on the camera and lens combination having published correction data available, and it genuinely can't fully undo the visible effect on every subject, lens or focus distance combination.