1. Binoculars for a variety of pursuits

Various scenes where binoculars are used

Binoculars are essential for bird watching. They allow birders to observe the movements and colors of the birds that cannot be seen with the naked eye. The best type of binoculars for observing birds are those that have a wide field of view that can quickly spot the bird whether it's in a forest, an open field, along the seashore, or on a lake, swamp or mudflats.

Binoculars are also useful at plays or concerts for capturing exciting scenes. They let viewers close in on the expressions on the faces of the performers, something that is not possible from a distance with the naked eye. They also significantly magnify the excitement at sporting events such as baseball, soccer, rugby, or horseracing. Viewers can share the spontaneous emotions that athletes experience at decisive moments. There are even binoculars that let observers freely zoom from low to high magnifications. At museums, visitors sometimes use binoculars to enjoy the finer details in a work of art. They choose slim, compact binoculars that can be taken out in an instant.

Binoculars are even used for astronomical observations. People have the impression that astronomical telescopes should be used for such observations, but binoculars are actually better suited for viewing scenes such as the moon or constellations. An important feature of binoculars is that they can be taken out for use very quickly.

Another area where binoculars are used is in observations made from ships at sea. Fishing vessels, for instance, use binoculars to locate fishing spots by observing water surface conditions and the behavior of seabirds as they pursue schools of fish beneath the water surface. For such purposes, binoculars must not only be strong and durable but have a wide, bright field of view and be water-proof as well.

Binoculars are used in many ways, from our own daily life to the diverse world of industry.

2. "Porro prism system" and "roof-prism system"

Roof edge: Light flux is split at the roof edge. If the angular precision of two reflecting planes that form the roof edge is poor, image resolution will deteriorate.

Generally, a prism erecting system is included in binoculars, and these are called prism binoculars. Though the astronomical telescope is also a tool for viewing objects at a distance, the images in this case appear upside down and left-right reversed. Contrarily, prism binoculars produce images as they look to the naked eye. Prisms not only flip the images so that they appear as they do to the naked eye but they also shorten the light path's total length. Today, there are basically two different prism systems: the Porro prism system and the roof prism system.

The "Porro prism system" uses prisms invented by Pietro Porro, an Italian military officer, in the mid 19th century. In the Porro prism system, two triangular prisms are placed at right angles to each other to reverse the image.

The image-erecting design of the "roof prism system" comprises roof prisms. Since light can travel along a straight path from the objective lens to the eyepiece, the roof prism system can be more compact than the Porro prism system. Its problem, however, is that the right angle of the roof edge^* must be manufactured with impeccable precision; otherwise, the resolution of the image will be visibly impaired. High-precision machining technology is thus required in the manufacture of the roof prism system.

How the Porro prism system works

How the roof prism system works

3. Sharp, clear images—an achievement of Nikon sport optics

Effect of the "field flattener lens"
Left: With "field flattener lens"
Right: Without "field flattener lens"

Aberrations such as distortion and chromatic aberration are an issue for every optical device. As one example, when focusing on the center of the field of view the periphery goes out of focus; and when the periphery is brought into focus, the center goes out of focus. To address this challenging issue, a "field flattener lens" is used for the eyepiece which corrects the overall aberration and achieves a sharp image even to the edge of the field of view.

Highly uniform light transmittance with bright, natural color over the entire area of visibility has been achieved not only by multi-coating the surfaces through which light is transmitted but also by using "dielectric high-reflective multilayer prism coating" on the first prism of a "roof prism system."

A variety of binoculars with different optical specifications such as magnification, field of view, and brightness, as well as different sizes, weights, operability, and design, are being produced for various applications. Though Nikon now makes a wide range of optical products, the first product Nikon ever made was a pair of binoculars. Nikon has continued to respond to the growing diversity of customer needs for binoculars taking advantage of its rich track record in this field.

Dielectric high-reflective multilayer prism coating