This 16-35mm lens has three types of aspherical elements and uses Inner focusing and ring USM for silent and high-speed AF operation. It is also highly resistant to dust and water droplets.
A fast f/2.8 maximum aperture stays constant over the full focal-length range, meaning no variation in shutter speed will occur when zooming.
Ensures optimal flash metering by passing distance information back to a compatible EOS camera's E-TTL II flash system.