APO and aspherical. This very luxury optics provides outstanding sharpness wide open. Speaking of SUMMICRON, I strongly remember the first and second version which were very hard and almost draw the essence of the subject. I didn’t always feel like carrying them because they are big and heavy, but I must say that they are legendary. The new SUMMICRON is definitely an honor student. Aperture doesn’t affect the picture quality, and it’s neither too hard nor too soft. As this lens is so excellent, so I even want something peculiar. Leica users tend to admire something peculiar, so they may not like this lens. Meanwhile, this lens will be best for those who cannot tolerate the looseness of old lenses.