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Lenses for Leica M cameras
by M. Feuerbacher 2003
The fame of the Leica M system is not only due to the excellent make of the camera bodies. The other important component is the legendary quality of the Leitz lenses.
Many differnt aspect have to be considered to produce a good lens. The mechanical make, the reliability under extreme conditions, the durability, and, of course the optical quality. All these aspects are conscientiously addressed by Leitz. All published lens tests confirm the success of their efforts.
The optical quality of a lens is mainly determined by three factors, the contrast behaviour of the lens, its "sharpness" and the distortions. The latter two points can be formulated in three mathematically more strict conditions:
These conditions are opposed by lens errors, the most dominant of which (first order aberrations) are
Additional errors, determined by the size of the aperture, the lens fittings,the size of the front and rear elements, and the total focal lenght, are vignetting and diffraction.
Objective lenses are composed of groups of positive and negative lenses of different focal lengths made of glass with different refractive indices. These are the main parameters that can be varied to cope best with the imaging errors under the given conditions.
Further criteria for lens design are the coatings (which should minimize reflections for a wide spectral range and which should, at least for the outer lens surfaces, be mechanically hard).
The Summicron 2/50
Six-element Gauß type lens (four groups) with five planar lens surfaces. A fast lens with highly balanced imaging properties. High image contrast, high sharpness up to the image corners, even at full aperture opening. Very low dependence of the imaging characteristics on the focusing distance. Coma free. Free of vignetting at f/4 and higher. The Summicron shows significantly less distortion than the Summilux.
Length 42mm, Weight 195g, Filter 39mm.
The Summicron 2/35
Seven-element Gauß type lens (five groups). A fast lens with highly balanced imaging properties, which is outstandingly compact. High image contrast, high sharpness up to the image corners. Imaging errors are further decreased at f/5.6 and higher. Very low dependence of the imaging characteristics on the focusing distance. Coma free. Low vignetting.
Lenght 26mm, Weight 150g, Filter 39mm.
Leica M lenses couple to the rangefinder in the camera body via a wheel running on a cam in the lens barrel. The cam is displaced according to the distance setting by a differential helicoid, such that the cam is always shifted parallel. This is in contrast to the C-Summicrons for the Leica CL and Minolta CLE, where the wheel runs on a tilted surface.
Leica M lenses are always delivered with an appropriate shade. The Summicron 35 has a rectangular and the 50 a round shade. Both have windows in order to minimize cropping of the viewfinder image. For the 50, a special lens cap attaching to the inverted shade was designed.