Optical demands and mechanical con- struction

Chapter 7

Leica R-Lenses	3

__Optical demands and mechanical con- struction

The design has 11 elements in 8 groups and employs two aspherical surfaces, one at the first surface of the front ele- ment and one at the second surface of the last element, incidentally the same as in the original Noctilux 50 mm f/1.2.

The lens has three moving groups that are being guided in milled slots with a precision of 0.010 to 0.005 mm.

The challenge for the Leica engineers was to design a lens that had to fit into three dimensions of requirements: per- formance, haptics and cosmetics. These dimensions are partly at conflict with each other. And we have to add anot- her dimension, that is the manufacture of the lens. In this area Leica has learned a lot from the previous designs. The main problem area is the narrow tolerance band for the manufacture and assembly. The lens consists of eleven lens elements, that are precision grinded and have a surface tre- atment to reduce surface irregularities to a sub micron level, in fact here we are talking about tolerances at the nanometer scale (0.001 micron). To deliver the required and calculated performance, the lens element must be fitted into the mount without any stress, as the slightest strain on the lens will deform the surface and produce unwanted optical aberrations. One should be aware that the accurate and strain free mounting of the lens elements is a big chal- lenge. There are additional challenges too: a lens element needs to be blackened at the sides to reduce the possibility of flare. This is accomplished by painting the sides of the lens with a black paint, still done by hand by experienced workers. But a thick (relatively speaking!) elastic layer implies that the lens could move ever so slightly within the mount. One solution might be to press the glass element into its mount, but too much pressure is not good at all. So one has to carefully balance the thickness of the layer of paint with the requirement of a strain free fitting.

In the area of lens grinding and shaping we are operating on a nanometer dimension. The jump from this optical dimension to the mechanical dimension of the mount and

the accuracy of assembly is a jump from nanometer scale to micrometer scale (0.001 mm), but this micrometer scale is still incredibly small. And the designer must be aware of this jump to assure that his calculations can be met in the realm of manual assembly, even when using sophisticated instruments to check the precision of the assembly. The new zoomlens has more than 40 main mechanical parts (excluding the elements and electronics and the aperture mechanism) that have to be assembled with a precision of 0.010 to 0.005 mm.

One of the biggest problem areas in lens assembly is the possible decentring of lens elements. Decentring of lens elements can be a tilt or a lateral displacement (relative to the optical axis) and will occur almost always during lens assembly unless one can work with very narrow tolerances. Most optical programs have a special module to study the effects of decentring and can indicate how much decen- tring is allowable before one sees a deterioration of the image quality.

Decentring in general brings loss of contrast and more astigmatism. A special construction is required to ensure that the very tight tolerances that this lens demand (due to the mechanical and optical constraints of a 1:3 zoomrange). The manufacture of parts can never be done in a zero-tole- rance environment. Therefore a certain amount of tolerance in the system must be accepted. In general one can appro- ach this problem in three ways: one can allow for adjust- ments during the assembly process and try to pair plus/minus parts to get the correct fit (old Leitz method), one can do a Monte Carlo statistical analysis to investigate where the most sensitive problem areas are and distribute the problematic aspect through the system by relaxing the constraint (Zeiss method of relaxation) and now Leica uses a third method. This is the method of mechanical compen- sators that are part of the mechanical construction and are already taken into account at the stage of optical design and calculation. This is the novel idea. Compensators them- selves are not new as a technique. In this case the lens ele- ment can be displaced by a small amount by a mechanical movement before being fixed in place. The displacement is controlled by a MTF measurement at a very high scale of magnification

New too is the approach to design the lens optically and mechanically at the same time and in full interaction. The designer must be aware what is possible at the assembly stage as he cannot demand the impossible from the people during their work. The optical calculations are optimized to

R-Lenses specifications

Leica R-Lenses have long been revered by photographers for their exceptional quality and performance. Designed for use with Leica R-series film and digital cameras, these lenses embody the brand's commitment to optical excellence, precision engineering, and user-friendly functionality.

One of the most notable features of Leica R-Lenses is their superb optical design. Each lens is crafted using high-quality glass, often featuring special elements such as aspherical glass and low-dispersion lenses to minimize aberrations and enhance sharpness. This meticulous attention to optical performance ensures that images captured with R-Lenses exhibit remarkable contrast, clarity, and color fidelity, allowing photographers to achieve stunning results.

Another key characteristic of Leica R-Lenses is their robust build quality. These lenses are constructed with durable metal housings, ensuring they can withstand the rigors of professional use. The precision of the manufacturing process results in smooth focus and aperture adjustments, providing photographers with a tactile and reliable shooting experience. The use of weather-sealing in certain models allows for shooting in challenging conditions, further enhancing their versatility.

Leica R-Lenses also feature a distinctive aesthetic, characterized by their sleek design and distinctive red dot logo. This iconic branding signifies a level of craftsmanship and quality that is synonymous with the Leica name. The manual focus mechanism on R-Lenses is particularly praised by many photographers, as it allows for fine-tuned control over the focal point, which is especially useful in portrait and macro photography.

In addition to their optical and mechanical excellence, many Leica R-Lenses come equipped with advanced technologies. For instance, some models include the ROM (Read-Out Memory) contacts, which enable the camera to communicate with the lens for enhanced functionality, including automatic aperture control and accurate exposure readings. This integration of technology with traditional craftsmanship exemplifies Leica’s approach to modern photography.

Ultimately, Leica R-Lenses offer an unparalleled combination of optical brilliance, robust construction, and user-friendly features. With a range of focal lengths and specializations, from wide-angle to telephoto, photographers can find the perfect lens to suit their creative vision. Whether one is capturing landscapes, portraits, or close-up details, Leica R-Lenses provide the quality and precision expected from one of the world’s leading camera manufacturers.