NIKKOR - The Thousand and One Nights No.31

Ai Nikkor ED 200mm F2S (IF)

Tonight, I would like to talk about Ai Nikkor 200mm f/2S IF-ED, which was developed based on the requests by press photographers. What kinds of anecdotes are there about this lens developed for the purpose of photographing indoor sporting events? How was the world's fastest 200mm lens developed? Let's look at the progress of development of the lens, step by step.

by Haruo Sato

I. Press photographers and NIKKOR

As I mentioned in Tale Eleven, Nikon (named Nippon Kogaku K.K. at the time this lens was developed) has had a very good relationship with press photographers. In fact, a considerable number of NIKKOR lenses have been born following the requests by press photographers. Among others, many telephoto and super telephoto lenses have been developed for historical events based on the valuable advice of press photographers. For example, Nikkor 400mm, 600mm, 800mm and 1200mm, which use the focusing unit, were developed for the Tokyo Olympics. The ED 300mm f/2.8, I introduced in Tale Eleven, was intended for shooting the skiing events in the Sapporo Winter Olympics. This means a succession of NIKKOR lenses had been capturing the instants where a long list of world records were made.

We praised and celebrated athletes and their great victories through the NIKKOR lenses. I'm sure that those who were involved in the design and development of the NIKKOR lenses felt a glow of pride, since they had been working on the projects concerned with preserving memories through pictures that go down in history.

The 200mm f/2, which I'll introduce tonight, was mainly intended for shooting gymnastics events. The wish of press photographers at that time was for a lens that would allow hand-held shooting and offered the fastest possible aperture, with a focal length of about 200mm. Ai Nikkor 200mm f/2S IF-ED was the answer of Nippon Kogaku K.K. (the present Nikon) to that wish. In those days, this lens was regularly used by the news media throughout the world to help providing a number of memorable photographs.

II. Progress of development

Now, let's look at the progress of development of Ai Nikkor 200mm f/2S IF-ED. The optical design was completed in 1976. The drawings for volume production were released in November the same year. The volume-produced items were first launched in April 1977 under the model name of Ai Nikkor 200mm f/2 IF-ED, only for the news media. The limited sale was continued for a while and then, in April 1982, the sale to general users was started under the model name of Ai Nikkor 200mm f/2S IF-ED. Thereafter, in order to protect the ED (Extra-low Dispersion) glass, a protective filter was added to the front lens, followed by a redesigned hood and an added gelatin holder, and then, the Ai Nikkor 200mm f/2S IF-ED New was put on the market in December 1985.

The designer of the optical system was Mr. Kiyoshi Hayashi, assigned to the then Optical Section 1, Optical System Department. To tell the truth, Mr. Hayashi was a master teacher (supervisor) of mine; I worked for a long period of time under his guidance since I joined Nippon Kogaku K.K. To my surprise, the Ai Nikkor 200mm f/2 IF was the first lens Mr. Hayashi designed. In those days, design automation was not in practical use, and calculators were also far behind the modern computers in ability.

The optical design at that time consisted of the determination of the power arrangement to define the fundamental configuration of the lens system, and the rough selection of Petzval sum and principal points to define the approximate overall length and back focus. Then, consideration was given to the number of lens elements and configuration. Next, a numerical table (change diagram of aberration) was prepared, showing how the lens performance varied with slight changes in curvature radius of individual elements, lens thickness, lens-to-lens spacing, glass refractive index, degree of dispersion and other factors.

Based on this change diagram, persistent efforts were made to find methods to effectively minimize aberrations. It was a steady, laborious task. The change diagram helps determine which and to what extent of aberration would be caused by slightly changing the individual element curvatures, element spacing, lens thicknesses, refractive indices and dispersion. In addition, it helps us to perceive how aberration could be reduced by combining the changes in this and that curvature, leading to find methods to minimize aberrations. Opening our eyes wide to look hard at the change diagram, we used to write notes with colored pencils. That was one of the essential tasks for designing lenses in those days. Mr. Hayashi also looked into the change diagram in silence every day, and succeeded in completing the lens which offered specifications no one had been able to achieve so far, after having a hard time. I think it is safe to say that this success in his first assignment decided his future course in his career. Thereafter, Mr. Hayashi was involved in the development of many IF (inner focusing) type ultra telephoto lenses in succession. Later, in 1994, he received the Award of the Chairperson of the Japan Institute of Invention and Innovation (JIII) for his achievements with his master teachers Mr. Nakamura and Mr. Arashida, in the presence of member of the Imperial Family and government officials. The developments by Mr. Hayashi and his colleagues became the origins of the IF type ultra telephoto lenses developed thereafter both inside and outside the company and all over the world.

III. Lens Performance and Imaging Characteristics

First look at the cross-section. The two front elements are made up of ED (Extra-low Dispersion) glass. The three elements including these two ED glass-made elements in the front group constitute the most important front lens for the telephoto lens. From the viewpoint of optical design, the three elements must sufficiently compensate for chromatic aberration, spherical aberration, and lower coma. The three-element front group is followed by the concave, focusing group of three elements. This concave group is designed to provide a telephoto ratio and also focusing function, which is the critical part of the development by Mr. Hayashi. The higher the power of this concave group, the greater the residual aberration in the front group, and the close-range aberration fluctuation is also increased. In consideration of the shorter focal length of 200mm, Mr. Hayashi did not select a larger telephoto ratio. This selection was a recipe for success for this lens. In addition, a unique configuration is seen in the last convex group. The last concave element in this group acts to reduce the Petzval sum. The addition of this one concave element made it possible to cover the angle of view of the 200mm lens.

Now, let's examine the imaging characteristics of this lens based on long-range photos, sample photos and design parameters. At full-open aperture, the lens provides reasonable sharpness and soft representation due to the resultant smaller depth of focus. The tight-focused areas yield higher resolution and proper contrast. In terms of design parameters, when strictly evaluated, the peripheral image is likely to become slightly unsharp due to the effects of the curvature of field and coma as it approaches the periphery from the center, which was, however, less noticeable in the actual shots. The sample photos were all shot at full-open aperture. Sample 1 was taken in proximity to the closest point, and Sample 2 was taken at a relatively medium distance. Pay attention to the hair and eyelashes in Sample 1 and the nap of the clothes in Sample 2, and you should be able to see how this lens provides sharp imaging characteristics. This lens provides sharpness even at the full open aperture, and it improves the sharpness when stopping down to f/2.8 to f/4. At f/5.6 to 11, the sharpness is further improved, resulting in almost uniform image quality. At f/16 to 22, the image quality is gradually decreased due to the effects of light diffraction.

Profile of Mr. Kiyoshi Hayashi

Mr. Hayashi is always mild, gentle and openhearted. When he was young, he regularly used range-finder cameras, so he loved cameras and lenses. Mr. Hayashi has many interests, but he is particularly interested in music. He has been studying about classical music (modern and contemporary music) in three Caucasian countries (Armenia, Georgia and Azerbaijan), with which most of us are unfamiliar. His interest in the Caucasian music is so strong that he has reached a professional level, going beyond the appreciation of music. He also has a profound knowledge of the conditions and historical backgrounds of the individual countries, not only the music, so we've been deeply impressed with his extensive knowledge.

Mr. Hayashi is also a gourmet, and he has a thing about fried meat cakes in particular. This is a story when I was young. Mr. Hayashi used to profess a great like for fried cakes of minced meat, saying "I'm very fussy about fried meat cakes." However, despite his profession, he always ate up fried meat cakes with great relish without being particular about restaurants. On one occasion, I asked Mr. Hayashi: "You simply love those fried meat cakes, don't you?" Smiling grimly, Mr. Hayashi answered with a single word. "You know it." All those present in the workplace broke into a laugh. Mr. Hayashi did have a very unique side since old days.