Update: A field test of these binoculars is now being done.
In April 2017, Nikon has
announced the
new Nikon WX Super-wide field binoculars for use in astronomy.
These binoculars are remarkable, because they are squarely opposing
common trends in high-end binocular design, which generally favor
compact, lightweight and easy to handle all-purpose binoculars.
The following table contains a subset of specifications, which
clearly demonstrate the unique mix of properties of these devices:
| � | Real angle | Apparent angle | Apparent angle | Eye relief | Close focus | Weight |
| of view (deg) | ISO-Norm (*) | angle-condition (**) | (mm) | (m) | (kg) | |
| Nikon 7x50 WX | 10.7 | 66.6 | 74.9 | 17.7 | 12.3 | 2.42 |
| Nikon 10x50 WX | 9 | 76.4 | 90 | 15.3 | 20 | 2.51 |
(**) The angle condition is the product of real angle and magnification
The new binoculars are equipped with huge angles of view, exceeding everything offered before on similar instruments. Nikon specifies the apparent (subjective) angles following the ISO Norm 14132-1:2001. This norm assumes the complete absence of distortion and yields a purely theoretical value. Similarly, the angle condition, being the most common approach to estimate subjective angles, assumes the presence of a considerable amount of pincushion distortion. In reality, subjective angles are measured somewhere in between both limits. I have inspected both binoculars on the IWA in Nuremberg and observed rather low levels of pincushion distortion in their images, so that the ISO specification is certainly closer to the truth than the angle condition. I would urge Nikon to publish the precise (laboratory) values here, because computed specifications are often so vastly different at these wide angles.
There exist further unusual properties of these instruments: They are focused individually at their eyepieces, and their close focus distances are comparably huge - both features in fact suggesting applications primarily in the field of astronomy, although any long distance terrestrial observations, for example from elevated scenic outposts, should yield outstanding results, too. The considerable weight of this binocular of about 2.5 kg suggests it to be mounted on a tripod. The instrument is sufficiently compact that handheld observations seem possible whenever the ellbows find a suitable support. We shall now take a look inside and see what these monsters have to offer:
Visible to the left is an air-spaced doublet objective, followed by an Abbe-Koenig prism. As the patent application (link at the bottom of the page) indicates, the eyepieces are more complex than shown in the sketch, since cemented faces between lens elements are invisible. Between prism exit and prime focus, there exists a block consisting of either 3 (7x50) or 4 lens-elements, which serves as the field-flattener system. The remaining part of the eyepiece is composed of four groups in a 2-1-1-2 array, so that the total number of lens-elements amounts to 9 (7x50) and 10 (10x50). The patent application offers five eyepiece examples, the first two of which would yield 7x magnification, while the remaining three would definitely fit to the 10x50 version. I have selected and sketched two of them which are possibly quite close to those implemented ones (the five examples differ somewhat in their distortion patterns, which excludes some of them).
Left: possible 7x50 eyepiece, right: possible 10x50 eyepiece; inspired by the EUROPEAN PATENT APPLICATION EP 3 495 866 A1.
According to Nikon, these eyepieces had been derived from their NAV-HW line of wide-angle astro-oculars. Altogether, this is quite an impressive setup, and the binocular may be submerged under water and remain waterproof up to 10 minutes at a depth of 5m (Nikon laboratory specification). We shall now address a couple of questions which may arise when discussing these unusual binoculars.
We may then safely assume that the entrance width, w, of the prism is of
the same order as Z. The volume of an ordinary Abbe-Koenig prism
is computed as V = 3.72 w^3 (see e.g. Paul R. Yoder, Jr., Daniel
Vukobratovich, Field Guide to Binoculars and Scopes, SPIE 2011).
We do not know the specific weight of the optical glass used for
the prism. At least the second element of the cluster
may be made of low index glass (BK7 has a specific weight of
2.5 g/cm^3), while the first block may consist of high index
BaK4 (3.1 g/cm^3). We take a middle ground and assume 2.8 g/cm^3,
to obtain a weight of 772g. The figure to the left indicates that
Nikon has not spared efforts to cut away all edges from the
glass block that are not needed, and thus may have saved another
25% of the total weight. We would then end up with a weight
of roughly 580g per prism cluster. The cutaway image indicates
that the eyepieces, including field-flattener, contain a lot of glass, too, and
together with the objectives we may add another 400g to each barrel,
summing all glass elements up to something close to 2kg in
both barrels. It is then no surprise to read that the entire instrument
weights 2.5kg. This applies to the 7x50 as well as the 10x50,
because both certainly use identical prism clusters.
The picture to the left shows Dr. Hans Seeger during his
inspection of the Nikon 7x50 WX (March 2017 on the IWA).
Both, the 7x50 and 10x50 offer images that are superior to
anything I have seen so far in any binocular. The images
are not only very wide, but amazingly bright, of highest contrast,
almost sharp to the edges, and impress with their almost perfect
correction of chromatic aberration. Of course, the conditions
inside the exhibition hall have been far from being perfect
for the conduction of critical tests, and I would be eager
to continue my tests under realistic conditions in the field.
One or the other weakness may show up, but I can hardly imagine
that my first impression would fail me in this case: These are
the best binoculars ever produced, and as such they are, at
least to me, the most exciting introduction to the binocular
market of the century.
However, the prices of these devices are reaching a level of 6000 US$, and are certainly prohibitive to almost every amateur astronomer, even the most enthusiastic one. Another drawback is the weight of 2.5 kg, which is somewhat beyond the limit of comfortably handheld instruments. I would love to see extensions of the current WX line toward smaller devices. For example, a 7x35 with identical objective angle of 10.7 deg. and the same focal ratio as the 7x50 would yield a diameter of the intermediate image of about Z = 29.4 mm, and prisms that weight only 1/3 of the currently employed prism. Similarly, the diameter of the eyepiece would scale down, since its huge field lens would reduce considerably in size. The resulting 7x35 wide-angle instrument would possibly weight about 1.2 kg, were easily handheld and carried around.
Additional infos (thanks to Daniel Konrad for this find):
European patent EP 3 495 866 A1 (pdf-file)
Last modified: October 2022