From Manufacturer
This 24mm lens has a fast f/1.8 maximum aperture with macro focusing capability (minimum focusing distance is 7.1" for a reproduction ratio of 1:2.7). The 9-bladed aperture diaphragm obtains beautiful, circular out of focus characteristics. It incorporates a floating focus system and uses two aspherical elements for minimized distortion, spherical aberration and astigmatism. The lens front does not rotate during focusing, thus allowing the use of a "perfect hood" and the easy polarizing filters. Optical construction was created to minimize light falloff (darkening of the image corners) at maximum aperture-a big benefit particularly for digital cameras. Materials used in this lens are lead and arsenic free ecological glass.