Leica S 70mm f2.5 ASPH
The Summarit-S 70mm f/2.5 ASPH. plays the role of the standard lens in the Leica S-System lens-portfolio, and has a focal length corresponding to 56mm in 35mm format. In order to ensure its universal versatility, the Leica design engineers invested immense effort to guarantee superior image performance at maximum aperture and at all focusing distances. One of the eight lenses arranged in six groups features an aspherical surface, to minimise aberration effects. The two cemented elements are manufactured from glass with high anomalous partial dispersion, minimising the effect of chromatic aberrations. In addition, glasses with very high refractive indices work together with the aspherical element to almost completely eliminate monochromatic aberration effects. In order to achieve perfect image performance from infinity to its minimum focusing distance of just 50cm (~1.6ft), the last two lenses are constructed as a floating element that moves independently from the rest of the optical system when focusing. The Leica Summarit-S 70mm f/2.5 ASPH. is ideally protected against water droplets and dust and features a protective neutral glass filter that is included as a parameter in its optical design. The reward for the immense effort invested in its design and construction is a lens with extraordinarily good contrast performance wide open and at all other apertures that, even at its closest focusing distances, can be only marginally improved in the extreme corners of images by stopping down. With a value of only 1.2%, distortion remains imperceptible, and maximum vignetting of 1.4 stops at maximum aperture is so extremely low, ensuring that the Leica Summarit-S 70mm f/2.5 ASPH. delivers consistently dependable and superior image performance at all apertures and distances.
Distortion & Vignetting
Distortion is the deviation of the real image height (in the picture) from the ideal image height. The relative distortion is the percentage deviation. The ideal image height results from the object height and the magnification. The image height of 27.04mm is the radial distance between the edge and the middle of the image field for the format 30mm×45mm. The graph of the effective distortion illustrates the appearance of straight horizontal and vertical lines in the picture. Vignetting is a continous decrease of the illumination to the edges of the image field. The graph shows the percentage loss of illumination over the image height. 100% means no vignetting