This lens replaces the previous high quality L-series 28-70mm f/2.8 lens, with a lens of even greater caliber. The range has been extended to cover an ultra-wide angle of 24mm, which makes it ideal for digital as well as film shooters, and the optics are even better than before with two Aspherical elements and a totally new UD glass element. It's now sealed and gasketed against dust and moisture, and a new processing unit makes the AF faster than ever.