What makes this wide angle lens so unique is that it's the first EF lens to employ both a replicated aspherical element and a UD element to correct distortion and spherical aberrations and eliminate chromatic aberrations often experienced with wide angle lenses. It also incorporates a floating construction for remarkably high resolution and distortion-free images at all distances within the entire focusing range (9.84" to infinity, even at maximum 1.4 aperture). Its rear focusing design maintains a constant lens length and the front doesn't rotate, making it easier to use special effects filters and the bayonet mount lens hood. This lens accepts 77mm filters.