Pixiq

It has been said that the history of the Leica camera is also the history of 35mm photography. Certainly no one would argue with the fact that Leitz/Leica has influenced camera design and photographic style around the world. However, as impressive as this is, the history of Leica also includes the history of high-performance lens technology.

Today it is widely recognized that Leitz was the first optical company to utilize computers for lens design. Leitz’s in-house glass research laboratory also created thorium-free high-refraction lanthanum optical glass, and designed the first machine to grind and polish aspheric lenses on a production basis.

Without the continuous research into new types of glass, new manufacturing technologies, and sophisticated computer programs, combined with the exceedingly meticulous care in the manufacture of Leitz products, the fabled success of the Leica would not have been likely to occur.

For decades, Leitz lens designs have been known for their extraordinary performance characteristics. They set the standards for lens manufacture and image quality in 35mm format photography. This is still true today.

The Attributes of Sharpness

There are photographers who claim that picture sharpness depends exclusively on the quality of the camera and its lenses. There are others who believe that the cameras and lenses of today are all very good, so that, at least in practice, the film and processing determine the sharpness of the photograph.

Then there are the proponents of tripods, who insist that they are indispensable for sharp pictures. Seasoned photographers, of course, know from experience that every one of these factors contributes to a sharp image.

Experts agree that there are many other influences that affect the quality of an image, which include: lack of sharpness due to movement when shutter speeds are not fast enough, inaccurate focusing, the type of lighting, and others.

Naturally, one thing that is an essential prerequisite for photographic sharpness is the lens. If the lens does not deliver a sharp image, all other efforts to achieve sharpness are doomed to failure. This explains why interest in lens performance is so great these days. And since optical systems can be evaluated electronically, it is not difficult to compare the performance of various lenses using numbers and curves or by photographing test charts.

While technically minded photographers like to discuss the graphs that result from these measurements, pragmatists prefer to test their lenses by photographing a newspaper taped to a wall. Beginners in the field of photography willingly tend to select their photographic lenses on the basis of published test results, where the reader is often given the impression of absolute infallibility of this type of evaluation.

Judging Lenses

But are such tests truly objective and are they the best way to judge the optical performance of lenses (including those for the Leica camera) without reservations? Answers to these questions are best sought from Leitz experts who have researched this subject for many years. Because of the complexity of this topic a brief answer is not possible and the following represents an overview of several professional viewpoints.

Occasionally, lens tests published by a magazine cause some readers to question Leica quality, while others compare test results with their own experience. Some readers also question if the testing method was the correct one. It is quite understandable, therefore, that photographers have asked Leica to publish appropriate curves for Leica lenses. And why not, since experienced photographers constantly praise Leica lenses? Indeed, it is the preservation of this reputation for perfection in its cameras and lenses that Leica regards as one of its most important corporate goals.

It is Leica photographers who benefit most from this credo since it means continuing refinement of manufacturing technologies and tolerances, on-going research for new materials such as new improved optical glass, plus new designs for improved handling and greater versatility. This adds up to a constant effort to satisfy the many needs expressed by photographers. Leica is guided by the knowledge that its cameras and lenses are generally used for the photographic reproduction of three-dimensional objects, such as landscapes, people, animals, houses, flowers, and the like. This has a direct bearing on the design of Leica lenses.

Since Leica lenses are not optimized for the photography of flat test patterns, those who attempt to evaluate their performance with the help of test charts and MTF (Modulation Transfer Function) curves  will easily get the wrong picture. That is also the reason why test results published by respected magazines and institutes do not always agree with the experience of photographic experts and photographers. Lens tests have always been controversial. That also goes for the interpretation of so-called MTF measurements. Still, MTF measurements are definitely significant in the evaluation of optical systems. To assure its high standards, Leica Camera AG in Solms maintains modern testing facilities.

As straightforward as the principle of MTF measurement is, the equipment it requires is costly, and the measurements themselves require great care and experience. Although the experts argue about how these curves should be interpreted, they do agree that a great many measurements are necessary for a valid evaluation. The number of these measurements that popular publications use for their evaluations is generally far from adequate.

In addition, the MTF is only part of the OTF (Optical Transfer Function), whose other component is determined by the PTF (Phase Transfer Function). Among other characteristics of a lens that the PTF serves to evaluate is the coma of a lens, which is considerably more difficult to interpret than the MTF. An MTF curve also reveals nothing about color correction, unless MTF curves are generated for all the different wavelengths of light. But that would mean an unmanageable number of tests.

An additional problem is that only exceedingly costly apparatus can virtually eliminate measurement errors inherent in any testing system. The majority of the testing installations inadvertently introduce system-inherent errors into the final test results, which cause inaccurate evaluations of the imaging performance of different lenses. MTF curves measured with different instruments are often not comparable. Even when the measurements are accurate, generally for reasons of economy, they represent a mere fraction of what is essential for a thorough evaluation of the imaging performance.

Isolated results are thus published out of context, claiming to present an objective analysis of imaging performance that is not necessarily valid. The path of the MTF curve depends considerably on the plane of focus that has been selected, i.e., whether the image plane (measurement plane) that produces the highest contrast in the center of the image was selected, or whether an image plane was chosen that yields the best overall contrast across the field. Measurement of contrast as a function of focusing is critical, yet this is rarely mentioned in publications. Leica lenses generally perform even better in practice than they do on test charts and in MTF measurements.

This does not denigrate MTF measurements. It must be taken into account, however, that MTF is merely one of several considerations in the evaluation of a lens and that MTF applies to flat object or image planes. Lens tests should also include an evaluation of the mechanical components of a lens. Mechanical precision should receive proper emphasis during the evaluation, because mechanical performance is as important to the user as optical performance. Yet, has any test report ever mentioned that Leica lenses in many cases even satisfy military specifications for highest demands under the severest conditions? And which lens tester has ever noted that a finished lens is inspected by Leica Camera AG for no less than 75 points, including photographic tests in hot and cold environments, with temperature gradients from +20°C (+68°F) down to -20'C (-4 °F) and back again? Other features  ensure steady dependability and performance capability, even under extreme climatic conditions, for many years.

At this time, there still is no satisfactory means of achieving an objective evaluation by applying simple tests. In the final analysis, photographers must therefore draw on their own experience, or on the recommendations of recognized photographic practitioners. This book will clarify the performance capability of Leica M lenses by delving into the particular characteristics of each lens.