The lens consists of ten lenses in seven groups. It holds an aspherical lens-element and a floating element, which guarantee a high image quality to its minimum focusing distance of 0,7m. The lens ensures a superb colour correction with its three cemented elements and seven lens-elements with anomalous partial dispersion. Reaching from infinity to its minimum focusing distance the lens offers exceptional imaging performance with high contrasts across the complete focusing range.
The Leica Summilux-M 28mm f/1.4 ASPH. rounds off the range of high-speed M wide angle focal lengths. It offers excelent image performance over the entire image field even at full aperture and in the close-up range thanks to a „floating element“. With its exceptional contrast, the lens delivers the same recognized high performance level as the Leica Summilux-M 35mm f/1.4 ASPH., and in some respects actually outperforms it. The vignetting that is typical of every optical system is naturally more defined on a wide angle lens, particularly a high speed one like this, than on standard lenses or those with a long focal length. At full aperture in 35mm format it is a maximum, i.e. in the corners of the image, of around 3.4 stops, around 2 stops on Leica M8 models with their slightly smaller format. Stopping down to 5.6 visibly reduces this light falloff – to 1.8 and 0.8 stops respectively. Stopping down further does not bring about any notable reduction as essentially only the natural vignetting remains. Distortion is extremely low for a wide angle lens at a maximum of 1.1% , which is rarely noticeable in practice. A total of ten lens elements are used to achieve this exceptional performance. To correct color defects, seven of these are made of glass types with anomalous partial dispersion, while one has an aspherical surface.