Satoshi Fukumoto

4th Optical Designing Section, 1st Designing Department, Optical Engineering Division, NIKON CORPORATION

Mr. Fukumoto was in charge of optical design, and turned Mr. Nishioka's concept into a design for a functional prototype model. He has a wealth of experience in optical design including binoculars, and has also been in charge of designing astronomical eyepieces with a super-wide field of view.

Image quality is astonishing, but can it be productized?

The development project had started, but could it really be productized?
Problems were piling up: How could they realize a super-wide field of view while keeping a flat, sharp view all the way to the periphery with the long eye relief that eyeglass wearers need?

"To tell the truth, the difficulties cannot be compared with any other binocular projects I have been involved in. Making the field of view wider negatively affects the peripheral image: that is the nature of optical design. The key question was how to overcome this problem. When Mr. Nishioka told me his idea for the first time, most people around him said it was impossible."
Mr. Fukumoto, who was in charge of optical design for this project and successfully delivered a functional prototype with the expected image quality, looks back at those days.

He was also in charge of optical design for astronomical eyepieces at that time. Those eyepieces were able to realize sharp images all the way to the peripheries despite a super-wide field of view of 102˚ (Apparent field of view)*. As he proceeded with the design of those eyepieces, the direction the WX design should take began to become clear. *The value is obtained using the following formula:
Apparent field of view = real field of view x magnification

"Of course, binoculars and astronomical eyepieces are different", says Mr. Fukumoto. "For a wide field of view, a larger erecting prism and wider eyepiece diameter are better. But the size of binoculars is limited because of the interpupillary distance. Also they need to be held by hand so there's a limit to how much larger you can make them. The most difficult issue was how to reconcile the size, weight and specifications with the form of binoculars."

*Functional prototype (7x50) manufactured in 2010. This was the first breakthrough towards productization.

"Carrying out numerous small adjustments to the eyepiece structure, I went through various eyepiece designs. Then, at last, I was finally satisfied with the optical performance all the way to the periphery.
Once I'd achieved this, I wanted to make this into a real product and confirm its performance no matter what it took."
Two years and nine months on (February 2010) from Mr. Nishioka's proposal, a functional prototype was finally completed with Mr. Fukumoto's optical design, enabling people to experience the WX series field of view. People around him who had previously been skeptical were now wowed. Word about its "supremely excellent view" started to spread around the office. The prototype model's role was simply to confirm the optical performance regardless of the weight and design, but it was nonetheless the first breakthrough towards productization.

Four years and five months later (July 2014), a mockup was constructed via a 3D printer. Despite slight differences, this mockup closely resembles the finished WX series binoculars. By enabling people to actually hold it in their hands, the mockup advanced understanding of the project in the office. Combined with optimistic signs for prism manufacturing, this was another big step towards productization.
Nevertheless, a major obstacle still stood in the way.
To productize the WX 10x50 IF binoculars, there were crucial improvements that still needed to be made on the functional prototype.
The issue of improving image quality remained, but at this point Mr. Fukumoto changed departments and was succeeded by Mr. Tomita.

Mr. Fukumoto, "We attained edge-to-edge sharpness with a field flattener lens system designed exclusively for the WX binoculars. You might have thought they would be too big or heavy, and indeed, realizing both wide field of view and long eye relief makes binoculars larger and weightier.

Squeezing the world's highest-class optical technologies into this size was actually extremely troublesome."