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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.

Lens aberrations

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:

  • The lens should image an object point as a point in the image plane
  • The lens should image a straight line as a straight line in the image plane
  • The lens should image a flat object flat in the image plane

These conditions are opposed by lens errors, the most dominant of which (first order aberrations) are

  • Chromatic aberration - the dispersion of white light in the lens depends on the wavelength. This leads to smaller focal lengths for blue and longer focal lenghts for red light (for a positive lens)
  • Spherical aberration - the focal length of the central beams is longer than that of beams more distant from the optical axis. This is an intrinsic error of spherical lenses.
  • Coma - asymmetrical spherical aberration for oblique beam bundles and off-axis image points. Leads to complexly shaped broadening of off-axis image points.
  • Astigmatism - direction dendence of the focal length
  • Distortion - the transverse magnification is a function of the off-axis image distance. This error transforms squares to pin-cushion or barrel shapes
  • Field curvature - curvature of the of the focal plane for off-axis points

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.

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