With Canon L-series lenses, the ring USM and other mechanisms perform to professional specifications, regardless of the shooting environment. Every lens that bears the Canon name must deliver the same reliability. To ensure this, Canon maintains rigorous production quality control standards at every phase, from design of the optical array to engineering of the mechanical parts. Manufacturing tolerances for lens element spacing, tilt, eccentricity and other specifications are calculated in micron units. When necessary, lenses are fine-tuned one by one to maintain this high level of performance. Today, the unfailing support of professional photographers is the ultimate proof of L-series reliability.