The Canon EF 17‑40mm f/4 L USM delivers a smooth 2.4× zoom from ultra‑wide to moderate wide, with a constant f/4 aperture for bright, low‑noise images. Its silent ultrasonic motor ensures fast, quiet focus on full‑frame or APS‑C bodies, while the compact 9.7 cm length and 500 g weight keep your kit lightweight for travel and street shooting.