Breathing refers to the shifting of either the angle of view or the focal length of a lens when changing the focus, depending on the definition. The two definitions are not equivalent: a lens with a constant focal length will exhibit narrowing of the angle of view at closer focus, and conversely, maintaining a constant angle of view requires precise shortening of the focal length as focus is decreased, which some (often higher quality) lenses are designed to do. Lens breathing does not prevent one from racking focus or following focus with this lens, but it lessens the desirability of any type of focus adjustment, since it noticeably changes the composition of the shot. This is not to be confused with the suction and expulsion of air from within the lens as its internal volume changes.
- Rowlands, D. Andrew (2018). "Equivalence theory for cross-format photographic image quality comparisons". Optical Engineering 57 (11): 1. doi:10.1117/1.OE.57.11.110801. Bibcode: 2018OptEn..57k0801R.
- Tanaka, Kazuo (2001). Zoom lens without focus-breathing phenomena. doi:10.1117/12.450421.
- "SAMPLE - LENS BREATHING". hdslr35 on Youtube. https://www.youtube.com/watch?v=bIrJUFtYxiQ. Retrieved 13 June 2014.
Original source: https://en.wikipedia.org/wiki/ Breathing (lens). Read more