With an effective focal length range of approximately 27 88mm 35 mm equivalent the ef s 17 55mm f28 is usm is a powerful lens that delivers remarkable image quality the wide angle zoom allows you to capture more of every scene and add a new sense of space and perspective to your photography fixed aperture the large f28 aperture provides excellent results in low light conditions the aperture remains constant through the full focal length range allowing you to zoom from approximately 2