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Lens Polishing —
Hand-polishing spherical front lenses for microscopes.

Seiichi Yamagishi

Seiichi Yamagishi
First Production Division, Kurobane Nikon
Joined Nikon in 1978. Posted to the Nikon Yokohama plant and put in charge of polishing objective lenses for microscopes; transferred to the Nikon Group's Kurobane Nikon Co., Ltd. in 1998. Certified as Nikon Master Craftsperson in 2007.

Mr. Yamagishi is in charge of polishing the front lenses of objective lenses for microscopes. The lens element on the tip of an objective is known as the "front lens."

The smallest of these lenses has an aperture of between 1 mm and 2 mm. There are some that have a distinctive shape that is midway between spherical and hemispherical.

The objective lens of a microscope forms an enlarged image of the microscopic object under observation, and must have a short focal length in order to achieve a high degree of magnification. In order to obtain a distinct image, the lens must also capture as much light as possible. Hence, the front lens has a distinctive shape with a high degree of curvature.

Lens-polishing is becoming increasingly mechanized. However, it is difficult to entirely mechanize the polishing process for front lenses due to their distinctive shape, the high precision required and the variety of shapes. Mr. Yamagishi says that at present the best method is to shape the lens as required by the design by hand-polishing those parts that cannot be left to a machine. In recent years, however, the increasing digitization of observation (in terms of the use of monitors that make use of image-sensing devices such as CCDs) has led to demand for higher-precision objective lenses. Despite the name, the acceptable tolerance limits for "hand-polishing" are no more than a few micrometers.

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Objective lenses for biological microscopes: CFI Apo TIRF 60xH and CFI Apo TIRF 100xH

The hand-polishing process

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1. After undergoing pre-processing such as lapping, the front lens is attached to the tip of a metal rod known as a "hand-polishing rod." The front lens shown in the photograph has an aperture of around 5 mm—relatively large for a front lens.

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2. Polishing equipment is sometimes used for processes other than the final polishing, such as lapping. However, in order to achieve the distinctive shape of the front lens, a final hand-polishing is required.

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3. The center of the work stand is the polishing stand. Hand-polishing is carried out by pressing the lens onto the polishing plate. The polishing plate is rotated anti-clockwise, while the polishing rod is rotated clockwise. Rotating the rod at the precise speed and angle necessary requires skill.

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4. A loupe is used to check the surface of the lens for scratches.

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5. The dimensions are precisely regulated using a micrometer.

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6. A fully polished front lens. The smooth curvature of the surface and the high degree of transparency are something to behold.

Raising the level of skill among technicians

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Mr. Yamagishi says that higher-performance objectives necessitate a higher standard of polishing.

He plays a leading role in the training and guidance of accomplished technicians, in order to meet the rigorous precision standards for polishing that are necessitated by higher-precision objectives. Bettering the already considerable skill levels of technicians is no easy task.

In addition, technicians trained by Mr. Yamagishi are in charge of instructing younger staff members. High-level technicians are able to instantly determine the best method to use by feeling with their fingertips, and to put that into practice. The conventional wisdom is that 10 to 15 years training and experience are required in order to reach this level of expertise. However, due to a lack of technicians, faster training is required, and the current aim is to train technicians in around five years—no more than half the stated period.

Throughout the entire Nikon Group, very few people possess the skill of hand-polishing. However, this skill continues to be passed on in a reliable fashion.

Coming to love one's work

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Recalling the time at which he joined the company and was assigned to his post, Mr. Yamagishi says "I immediately felt that I wanted to spend my entire life working on lenses...even though I was not that good with my hands. This was because I was struck by the fact that small, precise lenses had to be meticulously polished by someone, one by one."

He recounts that as he learnt techniques from his senior colleagues, he came to enjoy his job more and more. "I would like lots of people to know that—clumsy as I am—I have been chosen as a Nikon Master Craftsperson. In order to become a fully fledged technician, it is more important to strive to overcome one's clumsiness and to love one's work than to possess manual dexterity. It is by loving one's work and persisting diligently in one's task that one acquires skills."

Mr. Yamagishi turns the polishing rod while looking at the front lens and the polishing plate. He alters the speed and angle at which the rod is turned, judging the progress of the polishing by feeling with his fingertips. Simple as it looks, hand-polishing work involves a high degree of skill built up over the course of many years.

Clumsy people try harder

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Mr. Yamagishi has a unique perspective: "There are those who say that they are unsuited to doing delicate work because they are clumsy. However, they are wrong. It is clumsy people who better rise to the challenge of high-level tasks. This is because the clumsier someone is, the more they must learn and practice in order to make the grade. In doing so, they build up greater knowledge and experience than people who possess more natural aptitude and dexterity, and acquire greater perseverance. Those who can persist in the face of adversity make better technicians."

Mr. Yamagishi maintains that technicians who have overcome a number of adversities make good instructors. This is because they can tell the next generation about the barriers that they themselves have had to overcome on the way to acquiring their skills.

With this conviction, Mr. Yamagishi was able to turn his weakness into strength, and this is indicative of his strength as an individual.


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