The Nikon WX binocular is nothing short of an optical marvel.
Designed specifically with stargazers in mind, it addresses the demands of high fidelity representation of the toughest subject imaginable--stars. Point sources reveal optical aberrations more readily than any other target. Nikon pulled out all the stops in order to present star fields with unprecedented crispness across a very wide field of view.
ED objectives, huge Abbe-Koenig prisms, field flatteners, massive eyepieces, and multicoatings combine to create an immersive image like no other. The excellent edge-of-field correction, at such a wide angular field of view, puts the WX in a class of its own. All who dare to have their expectations in optical excellence irrevocably raised are instantly stunned at the first glimpse.
ED glass elements employed in each tube compensate for chromatic aberration that causes color fringing at the very edge of the field of view. Multiple ED Glass elements result in a contrast-rich and high-resolution image. All lenses and prisms are free of lead and arsenic, under the Nikon Green Procurement Standards.
Abbe-Koenig prisms, which feature total internal reflection on all surfaces and a high transmission efficiency, are utilized for a uniformly brighter field of view. Phase-correction coatings on the roof (Dach) surfaces compensate for phase shifts of light when reflecting inside prisms, resulting in high-resolution, high-contrast images. Another benefit is a slim body design.
A field flattener is integral to the optical design. It mates the field curvature of the objective to that of the eyepiece, delivering a sharply focused field from center to edge. The effect of pinpoint star images everywhere across the very wide field yields a view that is as true to life as can be obtained.
The front of the bodies are threaded to accept 55mm filters (P=0.75). This is a far superior location to that at the rear of the eyepiece, as is done for some other binoculars. A front mounted filter does not rob eye relief, does not become smeared with eyelash oils, and does not suffer loss of efficiency due to more extreme angles in transmission. This latter aspect is particularly true for moderate and narrower bandpass filters as designed for emission nebula observation.
Despite some incorrect myths, a humble 50mm aperture is quite amenable to the employment of nebula filters. This author does so regularly. A pair of 2" UHC type filters adapted via step-down rings will present wonderful views of larger yet dim nebulae such as the California and North America/Pelican, among many others.
Curiously, Nikon states the apparent field of view (AFoV) to be 66.6 degrees, based on an ISO 14132-1:2002 standard calculation. Such an AFoV would certainly be impressive enough. But we measure it via a projection technique to actually be 71 degrees. The discrepancy arises, at least in part, because the ISO calculation does not take into account the actual distortion (variation in image scale with field angle) characteristics of the instrument.
Tests in a darkened warehouse using a brilliant LED light reveal remarkably well controlled internal reflections, as well as an agreeably dim diffraction spike induced by the roof prism. There is a single very slim false exit pupil segment that lies too far from the principal exit pupil to possibly enter the observer's iris. Together with the excellent baffling against stray, the resulting image contrast is superb, even under extremes of illumination from intra- and extra-field sources.
The diopter adjustment ring employs a straight helicoid design. Eyepieces move back and forth in a straight line, and the lenses themselves do not rotate, ensuring the optical axis is not decentered during diopter adjustment.
Turn-and-slide rubber eyecups with six-click adjustment facilitate easy positioning, and click intervals become finer as the eyecups are extended, for easier adjustment for non-eyeglass users. We measured the 'real', effective eye relief from the rear surface of the fully retracted eye cups to be about 16.4mm. This permits to see the field of view for users who must wear eyeglasses.
The instrument is a waterproof structure that can be submerged to a maximum depth of 5m (16.4 feet) for 10 minutes. (Not designed for underwater usage). The airtight body is nitrogen-filled, preventing the interior of the optical system from fogging, and it resists mold even with significant changes in temperature. The operating temperature range of -20C to + 60C (-4F to +140F) permits use in severe conditions. Magnesium alloy is utilized in body construction, resulting in a sturdy, lightweight instrument that facilitates handheld viewing, although mounting is recommended for extended observation.
For mounting and carrying, a dual-purpose handle/tripod mount is included. To protect and transport your investment, a sturdy aluminum case with fitted foam insert is provided.