Leica SUMMILUX-M 1:1,4/28 mm ASPH. Notice D'utilisation page 23

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% (pulvinate),
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 color dispersion (partial dispersion),
while one has an aspherical surface. To maintain performance in the close-up
range, one element towards the rear of the optical system is a "floating
element" that moves independently of the rest of the mechanism.
Summary: The Leica Summilux-M 28mm f/1.4 ASPH offers maximum image
performance with a focal length / speed combination previously unavailable in
the M system. This extends the composition options of M photography,
particularly for available light shots, but also thanks to a previously unattainable
reduction in the depth of field combined with large field angles.
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