The IR (infrared) setting is a red marking found on many camera lens mounts that indicates the focus adjustment needed when shooting with infrared film or infrared-sensitive sensors. Infrared light focuses at a slightly different plane than visible light, and this setting helps ensure that subjects remain sharp when capturing infrared images.
Photographers using the IR setting can achieve accurate focus and improved image quality in infrared photography, whether shooting landscapes, experimental compositions, or scientific subjects. Knowing how to use the IR setting is essential for creating crisp, well-focused infrared images without relying on guesswork.