Apochromatic colour correction and an aspherical lens surface are combined for the first time in this lens of this type. Of its five individual elements, two are made of high-refraction glass, while two others feature anomalous partial dispersion. Its brilliance and quality of resolution are exemplary even at full aperture. Light falloff is very low. Its fast aperture, for a 90mm lens, lets you shoot at relatively short exposure times even in dim light, helping to minimise the effects of camera shake, for instance when photographing street scenes from a distance.