In 2002, Leica introduced the fourth version of their popular Summicron-R 90 mm f/2 Asph portrait lens in the form an Apo model, consisting of five elements in five groups.
It was the first lens with apochromatic correction to also feature an aspheric surface. Two of the five elements were made of high-refraction optical glass, with two further elements offering anomalous partial dispersion. As a result, rendition and resolution were excellent across the entire image plane, even at full aperture – a trait that set the lens apart from its predecessors.
Vignetting had also been reduced on the new Apo version, so that it was minimal even at full aperture. The high light sensitivity, as well as the lens's excellent contrast rendering allowed for a particularly bright viewfinder image, which in turn enabled precise focusing even in low light.
In addition, the optional Apo-Extender-R 2x made it possible to transform the portrait lens into a moderate, 180 mm f/4 tele lens.