Breathing in photography refers to the apparent change in field-of-view when a lens focuses at different distances.
While traditionally breathing encompassed any geometric change in the field-of-view resulting from focus adjustments, even if the angle-of-view remained constant (due to changing distortion), the term has more recently been used to describe the change in a lens's effective focal length as its focus distance changes. This is more apparent in some lenses than others.
Here's a breakdown:
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Original Definition: Any alteration in the geometric field of view as the lens focuses, which can include changes in distortion even if the overall angle of view stays the same.
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Modern Definition (and More Common Usage): A noticeable change in the focal length (and thus magnification) of a lens when the focus point is shifted from close to far, or vice-versa. This appears as if the image is "zooming" in or out slightly during focusing.
Why does breathing happen?
Lens breathing is an inherent characteristic of lens design and construction. It stems from how the internal lens elements move to achieve focus. The extent of breathing varies across different lenses. Prime lenses tend to exhibit less breathing compared to zoom lenses.
Impact of Breathing:
- Videography: Breathing can be distracting in video recordings when focus is adjusted during a shot. A noticeable shift in magnification can disrupt the visual flow.
- Focus Stacking: In macro photography, breathing can create issues during focus stacking, as the apparent image size changes between shots, making seamless merging difficult.
- General Photography: While less critical in still photography, extreme breathing might slightly affect composition across varying focus distances.
Examples:
- A lens might appear to be a true 50mm at infinity focus, but when focusing closer, the effective focal length might decrease to 45mm. This manifests as a slight widening of the image when focusing closer.
- Conversely, some lenses might appear to "zoom in" slightly as you focus closer, effectively increasing the focal length.
How to Deal with Breathing:
- Choose Lenses with Minimal Breathing: Research lenses known for minimal breathing if it's a concern (e.g., for video work).
- Avoid Rack Focus: In video, minimize large focus shifts during recording to reduce noticeable breathing effects.
- Correct in Post-Production: In some cases, minor breathing can be corrected in post-production software.
- Acceptance: For most still photography, slight breathing is often negligible and doesn't require correction.
