The Lumix 50mm f/1.4 is a no holds back kind of lens. It's big, it's a little heavy but it is built like a tank. Its been said that this is the new standard that all other Panasonic lenses will be held to because of its high quality optics. It has 13 lenses in 11 groups; 2 aspherical lenses and 3 ED (Extra-low Dispersion) lenses that come together to suppress chromatic aberration. It's tack sharp, weather sealed and with its dual motor auto-focus system you are sure to nail the shot no matter what conditions you are in.    

Lumix S1 + Lumix S Pro 50mm f/1.4