Focus Breathing

Focus breathing occurs when a lens changes its effective focal length as it adjusts focus distance. Moving focus from infinity to a close distance causes the angle of view to shift — the image may appear to zoom in or out slightly as focus changes. In still photography this is almost always imperceptible and irrelevant. In video, where focus pulls are a standard cinematographic technique, breathing causes the background to visibly shift in size as the focus moves from subject to subject, which is visually distracting and considered unprofessional in narrative filmmaking contexts.

Breathing is a product of the lens optical design and the mechanism used to shift focus groups. Internal focus designs where the front element does not extend as the lens focuses tend to breathe less than older extending-barrel designs, but breathing is not eliminated by internal focus alone. Some lenses breathe more than others regardless of their construction type. Cinema-specification lenses, such as those from Cooke, Zeiss, and other dedicated cine glass manufacturers, are engineered to minimise breathing because their professional use case requires follow focus pulls during shots.

For M43 video shooters, breathing is most relevant when shooting narrative or commercial content where focus pulls will be visible in the edit. Documentary and event video shot with continuous autofocus rarely involves deliberate slow focus pulls, making breathing less of a practical concern. When evaluating M43 lenses for video use, breathing behaviour is rarely specified in the manufacturer's documentation and must be assessed from real-world tests. The Panasonic Leica DG lenses and OM System PRO lenses tend to exhibit less breathing than budget alternatives, though this varies by specific lens.