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  6. Precision Glass Mold (PGM) Aspherical Lenses

Precision Glass Mold (PGM) Aspherical Lenses

The new PGM, the result of the engineers' efforts and Nikon's breakthrough technologies

We understand that major advances in molded-glass aspherical lens technologies have been incorporated in Nikon's new interchangeable lenses.

The combined efforts of the design
and manufacturing engineers have
taken the molded-glass aspherical lens
to new heights.

Sensui:

Yes, that's right. The AF-S NIKKOR 14-24mm f/2.8G ED we just released is a zoom lens that has better optical performance than the single focal length 14mm lens. The second element from the front of the 14-24mm lens is a PGM aspherical lens that has a very large aspherical surface (amount of divergence from the spherical surface) and a large diameter. Wide-angle lenses have inherent problems such as distortion and field curvature. The design department had for a long time wanted to somehow correct these problems. The most effective solution would have been to use an aspherical lens in the front, but this wasn't possible.

Was it difficult to make a large, deep lens?

Sensui:

Yes, the ultra-wide angle of 14mm demands a considerably large aspherical surface. When it is made using the hybrid method, the plastic section is thicker, making it more sensitive to environmental changes, so we really wanted to make it with glass. If we used the precision-ground method, the cost would have been too prohibitive, so we repeatedly asked the manufacturing division to use molded glass. But no matter how often we asked, we were always told that it isn't possible. Then about three years ago, we sent the proposal to Mr. Sakuma who had just been transferred to the manufacturing division, and surprisingly, he responded that he would accept the challenge. This provided us with a launch pad, and in the end I was able to achieve my goal since joining Nikon.

Sakuma:

The 14-24mm lens is the first wide-aperture lens that I worked on. Mr. Sensui's design division came to us and asked if we could make this kind of lens. I was there only a few months then and said that, based on past cases, we could not do it with conventional methods but that we could if we did a certain part a different way, and I passed this on to Mr. Ogata, who is directly in charge.

Mr. Ogata, since you were engaged in actual production, what did you think about it at the time?

The team's efforts have culminated in a breakthrough lens that features a larger aspherical surface and unprecedented shape.

Ogata:

I was very surprised when I first saw the lens drawing. It was much larger and deeper than anything we had made before. When we make a PGM aspherical lens, we produce the shape in stages, first from barrel and press material to a pre-form?the form just prior to pressing it into the die. When the pre-form and die for the tests arrived, I was at a loss to describe the unusual shape. I have designed pre-forms and dies before, but my impressions of the drawing and the actual product were completely different. I frankly thought it was impossible.

Sakuma:

I encouraged him while listening to his opinion, and together we continued to do everything we could. Anyone familiar with conventional technology probably would have said it was impossible to make such a shape. Of course, the process was a continuous struggle, but bolstered by Nikon's peripheral technologies that had been rapidly developed at the time, the 14-24mm lens was finally made. The process was repeated for the AF-S NIKKOR 24-70mm f/2.8G ED that followed.

Sensui:

At the optical design division, two young staff members with their first experience in lens design were in charge of both the 14-24mm and 24-70mm lenses. These two came to me and said they wanted to use that sort of aspherical lens, so we talked about it. I told them I thought the manufacturing division would reject it but that they should propose it anyway. So they did and Sakuma responded that he would do it. I couldn't believe they could do it and was surprised.

Sakuma:

The two staff members in charge of design came to Otawara, where Tochigi Nikon is located, to talk with me directly. We had a number of discussions and they really tried to persuade me. Having agreed to do it, we felt responsible for bringing it to fruition. We had peripheral technology breakthroughs and the support of the Nikon Core Technology Center, and in the end we succeeded in producing these two remarkable lenses.

Mr. Sakuma and Mr. Ogata, you both work at Tochigi Nikon and are in charge of development and manufacturing. What sort of work does Tochigi Nikon do?

Sakuma:

Tochigi Nikon makes parts and products related to lenses, mainly interchangeable lenses for SLR cameras. Aspherical lenses were first started at Nikon's Sagamihara Plant, and in 2000 the entire section moved to Tochigi Nikon.

Ogata:

Tochigi Nikon makes practically all the parts for interchangeable lenses. The company is engaged in integrated production from polishing and fabrication to assembly. We also do the Nano Crystal Coat, Nikon's latest technology. In addition to manufacturing, Tochigi Nikon also has equipment and facilities that carry out inspections and environmental tests.

Design and manufacturing talents are combined to produce even better products

What advantages do PGM aspherical lenses have from the user's standpoint?

The members exchange views from the
perspective of their respective
specialties to explore further
possibilities for the PGM aspherical lens.

Sensui:

Firstly, good performance. After that, compact size due to the reduced number of elements, and then, affordable prices. For optical products like the 14-24mm lens, users are more interested in performance than compact size. Users have given the 14-24mm high marks because it balances ultra-high performance with a relatively compact size.

How did the market react to the 14-24mm and 24-70mm when they were released?

Sensui:

They were released worldwide at the end of August 2007, at about the same time we announced the D3. At the time, we had professional photographers use the two lenses at the IAAA World Championships in Athletics and they were amazed at the performance just by looking through the finder. They said they finally had a wide-angle lens with a useable periphery around the picture. Both lenses were enthusiastically received, and they have won a variety of awards. The AF-S NIKKOR 14-24mm f/2.8G ED received an award at the recent Photokina.

Are aspherical lenses particularly effective in wide-angle lenses?

Sensui:

Yes. They're effective because they have the ideal shape for the various angles of view. With other lenses, such as telephoto lenses, color aberration is a more important issue. However, aspherical lenses do have some benefit in telephoto lenses in that they can reduce the number of elements. This improves lens performance and makes it lighter and more compact. At present, however, the front element of a telephoto lens is quite big, making it rather difficult to use an aspherical lens.

Is it possible you'll work on making a larger aspherical lens, with a telephoto lens in mind?

Sensui:

We're looking into it. We might send another unusual request to the manufacturing division!

Sakuma:

And we might say yes again! We have already received various requests from the design people, so we are inundated with plans for new product development. You've got lots to look forward to.

Ogata:

Molded glass is a technology with lots of possibilities for the future. I think other manufacturers will be especially surprised when they see the AF-S NIKKOR 14-24mm f/2.8G ED. I would like to attempt new shapes and levels of precision beyond the confines of existing ideas of what is possible.

Thank you very much.