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Nikon have produced some of the best porro-prism binoculars ever. These Nikon Marine 7x50s are made in Japan, just like their famous Superior E range, but do they give a similarly superior view?

Nikon Marine 7x50 IF WP Review

Nikon’s Marine 7x50s are a rare thing these days – a Japanese-made porro-prism binocular. Their spec’s are superficially similar to Nikon’s premium Prostar 7x50s, but they’re very different in reality. So are these some kind of sibling to Nikon’s outstanding Superior E line of porro-prism binoculars? Maybe a rubber-coated big brother to the 10x35 EII? Let’s find out …

At A Glance



Objective Size


Eye Relief

18mm claimed (12mm actual)

Actual Field of View

7.5 degrees

Apparent field of view

49.3 degrees

Close focus








Data from Nikon Europe.

Design and Build

Any idea that these are basically the same binocular as the Prostar 7x50 IF SP WP disappears as soon as you put them alongside: the Prostars are much bigger in every dimension and quite different externally; I can’t find a single common component. The 7x50 Tropical IF HP WP is undoubtedly similar to the Prostars; these Marines are not.

Even more confusingly, Nikon also seem to sell a central-focus Chinese-made Marine CF WP 7x50 model. I’ve said it before - Nikon, like Playboy, have more models than they should.

And what about all those two-letter abbreviations: IF? WP? IF- Individual Focusing. WP – Waterproof.

Body and Ergonomics

Compared to the Prostars, these look... not exactly cheap, just ordinary, and are covered in thin black rubber armour that looks just like that on a Minox. They don’t have that Prostar look of a piece of Navy equipment, or the fabulous level of engineering.

Nikon claim waterproofing for these, hence the name, but it’s to just 2m for 5 minutes – a lower level than the Prostars or Tropicals.

Internally the Marines also look well-made and of similar design to the Prostars, but the components are again all quite different.

Not only are they smaller than the premium Nikon 7x50 models, but the Marines are lighter as well, at 1170g.

The hinge is just Marked “AO Japan”, suggesting these might be a re-badged generic model, or at least outsourced (to Asahi Optical?). Confusingly, though, the prism housing bears the Circle-C ‘Criterion’ mark that once meant good things on a pair of Nikon 8x30 (or 10x35) Es, but that has generally fallen out of use.

Made in Japan, but maybe not by Nikon.


Like the Prostars and Tropics, the Marines have individual eyepiece focusing, which may be fine for scanning the horizon from the bridge of a yacht; or indeed for astronomy. But otherwise, it’s honestly a pain.

Individual ocular focusing. Deeply recessed eye lenses mean real eye relief is much less than claimed.

Optics - Prisms

These are a completely conventional porro-prism design.

Optics - Objectives

The objectives are much less deeply recessed than the Prostars’ and are held in by a single lock-ring.

They are properly multi-coated, but again the coatings aren’t quite up to the premium standard of the Prostars’. Nonetheless, Nikon claim 95% transmission, which is a very high level for any binocular: it that why they bear the ‘Criterion’ hallmark?

Full multi coatings are not quite as good as the Prostars’.

Optics - Eyepieces

The eyepieces are rubber covered and have a printed rather than engraved scale like the Prostars’. Flat eye lenses sit below thin, folding eye cups.

Next to the left ocular these are marked “7x50 7.5° WP ©”, so in theory they have a slightly wider field than the Prostars’.

Nikon actually claim larger eye relief for the Marines (at 18mm) than the Prostars (16mm), but in fact I measured just 12mm from the eyecup for the Marines, so the 18mm must be measured from the lens. This is borne out in use. Make no mistake, these have less ER than the Prostars, no matter what the brochure says.


Included are a fairly low-rent cordura case, stay on objective covers and a thin plastic strap.

Straps and case are cheap, generic items. Prostars have leather.

In Use – Daytime

Ergonomics and Handling

Handling is typical for a large porro-prism binocular. The Marines are heavy, but not unduly so. Individual ocular focusing is inconvenient for terrestrial use, much less so for astronomy and marine, where they tend to stay focused on infinity.

The View

The centre field is reasonably sharp and detailed, with decent colour rendition and good brightness. However, these are very hard to focus because the focus point is very indistinct, a sure sign of not-so-good optics. The main problem, though is extreme field curvature.

Overall the Marines are not a pleasant binocular to use in the daytime, due only to that very curved field, small sweet-spot and vague focusing.

Flat field?

These binoculars have terrible field curvature off axis, from only ~45% of the field width, so that theoretically-wider field in fact turns into a miniscule usable sharp area.

The field-curvature problem is exactly the same in both barrels and is not a fault – they were designed this way. The question is, why? Could it be that Nikon are assuming that centre field is all-important for marine use? That the grey expanse of waves on either side of the distant ship doesn’t matter much? Not unreasonable, I suppose, but it spoils the view for use on terra firma.

Chromatic Aberration

The Marines are sharp and CA-free on axis, typical of good external-focusing bino’s. But that’s the end of the good news. Off-axis, false colour increases a lot, just like every other aberration you can think of.

In Use – Dusk

The high-transmission optics and big objectives mean these perform well into dusk.

In Use – Observing the Night Sky

Surprisingly, once you get them focused (not easy with a vague sweet spot and individual focusing), the Marines work well for astronomy. Nikon claim a very high light throughput of 95% for the Marines and they certainly seem every bit as bright as the Prostars (but bear in mind that my exit pupils only go to about 6mm, not the full 7mm).

The heavy off-axis aberrations create a tunnel-like effect on the night sky, but I could learn to ignore it.

The Moon

The Moon looks decent, with minimal chromatic aberration. Little flare or ghosting is visible with the Moon in-field. With the Moon just outside the field there is some veiling flare and reflections off the side of the tube, but no more than is normal with mid-range bino’s.


Jupiter shows the moons easily as perfect points and the Jovian disk shows only a little spiking and flare (but more than the Prostars and other premium binoculars).

Deep Sky

Stellar images are not as tight as the Prostars’, but quite acceptable nonetheless. Star fields are nice and star-colours good: Albireo is easily split and an enjoyable sight with these. Enough of the field is visible and flat to take in most objects and the good light throughput means that these go deep and diffuse DSOs, like M33, are easy to find.

Perhaps at night it’s easier to ignore the off-axis aberrations, but I found the Marines quite usable for astronomy.

Nikon Marine 7x50 IF WP vs Nikon Prostar 7x50 IF SP WP

These binoculars share similar numbers, but not much else. To clarify that, here’s a quick synopsis of their differences:

·        The Prostars are a superbly made, heavy duty binocular. The Marines are just an ordinary mid-range model

·        The Prostars are much bigger and heavier and look totally different with leatherette vs the Marines’ rubber armour

·        The Prostars have a flat field; the Marines’ is horribly curved

·        The Prostars have sensible eye relief, the Marines too little (whatever the brochure says)

·        Both have individual ocular focusing

·        Both are waterproof (though the Marines less so)


The Marines are interesting because they make a point about binocular design. They are an unpleasant binocular for terrestrial use with way too much off-axis field curvature and astigmatism. But they still have modern glass and multi-coatings. This means that in the dusk and at night they will outperform even a super-premium 1970s binocular (a Zeiss Oberkochen perhaps), just because they let more light through, more light in fact than almost any roof-prism binocular.

In fact, these Marine 7x50s are also quite sharp on-axis. So they work rather well for astronomy, as long as you concentrate on the centre of the field, where stars are tight and bright, and ignore the time-warp tunnel effect from the off-axis curvature and astigmatism.

Should you buy them? Only if they are cheap as the proverbial, in which case they might make a good binocular to leave on your canal boat, your cabin cruiser, or perhaps in your observatory.

I habitually used to leave an old-but-good pair of Japanese 7x50s on the floor of my observatory for bored moments taking subs for imaging. Then the water main burst and flooded my dome, ruining the binoculars. These Marines would have doubtless have survived.

Not recommended except for astronomers looking for a ‘leave them in the observatory’ pair, or perhaps for their intended purpose on the bridge of a boat.