Consumer's Guide To Boat Binoculars

By Tom Neale

Look deeper than magnification when you're buying binoculars. There are models that stabilize, relieve eye strain, and have a built-in compass. Here's what to look for, from an experienced boater's point of view.

Photo of a person looking through binoculars

The first thing you notice when you're buying binoculars is a "value" such as 7x50. Those numbers give the degree of magnification and the diameter of the objective lenses. In 7x50 binoculars, the "7" tells you that the target object is magnified to seven times its size. More isn't necessarily better. For example, higher magnification reduces the field of view, making it more difficult to find a small object at sea. The "50" gives you the diameter of the objective (front or larger) lens. The larger that lens, the more light it will gather, a quality that's extremely important on a boat at night or in other low-light conditions. Doubling the size of the objective lenses quadruples the light-gathering ability of the binoculars.

Many feel that 7x50 is the best compromise for boat binoculars, but it's important to consider other features. One is the "exit pupil." This is the diameter, in millimeters, of the beam of light that leaves the eyepiece. A larger beam gives a brighter image, a great advantage at night. Theoretically the exit pupil should approximate the diameter of your eye's pupil after it has adapted to the dark. This decreases with age, but it's typically between 5 mm and 7.5 mm. Divide the size of the objective lens by the magnification to get the exit pupil in millimeters. If you cruise in low-light conditions regularly, say pre-dawn fishing trips, this is another reason not to buy a set with extremely high magnification.

Not So Fast

From these basics, you may think you have enough to make a good choice, but there's more. For example, "eye relief" is the distance that binoculars can be held from the eye without straining your eye while still seeing the full field of view. If you wear eyeglasses, this is especially important and you'll probably want at least 15-mm eye relief. Some better binoculars allow you to fold or otherwise adjust the rubber eyecup to help with this issue. Some, such as the Steiner XP Commanders, come with several different sets of eyecups.

Oh, Say, Can You See?

Light-gathering ability is critical for a boater. When I purchased my first set of high-quality binoculars many years ago, I was amazed at what I could see out in the ocean at night with starlight providing the only ambient light. It was very different from the cheap sets I'd used before. The size of the objective lens is important for this, but there's more involved. Color differentiation and sharpness are also concerns. We want not only to see that buoy at night but also to hopefully determine its color and shape. Many factors contribute to enhanced night vision, including quality of the glass in the objective and eyepiece lens, quality and type of prisms used (we'll get to prisms below), and lens coatings. The light transmission as well as color differentiation can be objectively measured by the manufacturer as the beam exits the eyepiece and the makers of more expensive binoculars strive to excel here as well as with other issues. Although the subject of lens coatings seems somewhat esoteric, it's not just smoke and mirrors. Coatings can do things such as reduce internal glare and light loss, which can yield better light transmission and brighter images. Coatings may also reduce internal fogging, helpful even if the binoculars are nitrogen filled. There are different levels of lens coatings, ranging from coated to fully coated, multicoated, and fully multicoated, the latter being the best. It means multiple coatings are on each lens.

Quality manufacturers go to great lengths to develop and apply proprietary coatings. One example would be what Fujinon refers to as its patented EBC (electronic beam coating). This is another reason why I wouldn't buy cheap binoculars. Resolution and contrast are important on the water. Poor quality here could make you miss a distant buoy or mistake its shape.

Porro Or Roof: A Prism Primer

Prism lenses are internal and sometimes called mirrors, although that term doesn't fully describe what they do. They reflect the image and, if made with high-quality glass, can help reduce internal light scattering and enhance the view in other ways. Binoculars typically used on boats have objective lenses at a wider distance apart than the eyepiece lenses. Many prefer this arrangement because they feel it gives the effect of more depth. This type of construction uses Porro prisms, which are rated BK-7 or BA K-4. Generally the BA K-4 prism has better glass and produces a better image. Binoculars with straight-line tubes (the objective and eyepiece lenses are in line with each other) are more compact and often lighter, but these require roof prisms that are far more complex and normally cost more.

A major failure of even very fine prisms occurs when an impact to the binoculars knocks one askew, even slightly. The image may become distorted or out of kilter, causing severe eye strain and making the set useless. Sturdy construction is critical. You generally don't get what you don't pay for; cheap construction often means early demise of binoculars.

Steiner, for example, says that it uses a special independent prism carriage system to protect them. In addition to cost, there are other clues indicating good construction. Manual assembly after use of computers in design and technology, as in, for example, cutting the glass for the lenses, is usually a sign of quality. Boat binoculars should also be encased in a shock-absorbent material such as rubber. A waterproof rating means that the set can not only be thoroughly splashed (a minimum requirement for boating use) but that it can be actually submerged, three feet or more, for a period of time with no water getting inside. Some sets even come with straps that'll keep them afloat if you drop them, and others will float on their own. Mechanical fastening of lenses to the chassis, as by threaded rings instead of glue or sealant, helps to insure seal and prevent shifting. Rugged fittings, such as those that secure the strap, also indicate quality.

Take A Test Drive

Many features, such as quality of the glass and coatings, are difficult for the buyer to evaluate except by the reputation of and statements by the manufacturer. However, it does help to use them before you buy. Although looking through binoculars in or just outside a store gives some indication as to how well they will work for you, it isn't as good as using them aboard.

But even at a dealer's location, there are some tests that may help you. For example, check ease of focus. With the Steiner Commander XP series once you've focused at approximately 50 yards, the set is focused for you from around 20 yards to infinity. Another test you can do is to hold the binoculars at arm's length, with the eyepieces facing you. Look through them at a light object such as a white wall. You are more likely to see a true circular image if there is good prism and optical design. And if you see a band of color perhaps somewhat like a rainbow at the edge of light-colored objects, this may indicate deficiency in the areas of sharpness and detail. A knowledgeable dealer should be able to assist you in making evaluations, particularly if he sells more than one brand.

Bear With Me

There are two additional features that you should consider: an illuminated bearing compass or stabilization. Stabilization has obvious benefits, is usually achieved electronically, requires batteries, and is impressive to use. Look at the vertical range of stabilization. If it's less than plus- or minus-5 degrees, you may be disappointed.

The bearing compass allows you to line up your target with a compass reading usually appearing at the bottom of your view. Look for the type of battery it uses (backlit for night use), the extent to which, if any, the compass readout at the bottom of your view interferes with your view, the ease of aligning the compass reading with the target, and the extent to which the compass is dampened. Too much or too little dampening will make it harder to get a real-time reading on a distant object.

No Perfect Pair

We haven't found a set that incorporates both of the above features as the components of the stabilizing equipment, such as electronics, would interfere with the compass in a bearing finder. Also, common sense dictates that if an image is stabilized, a bearing finder compass won't be able to give a real-time bearing, which could mean that the bearing is inaccurate with perhaps disastrous consequences.

My preference would be to buy a set of binoculars with a good bearing-finding compass. With practice you can compensate for the rolling of the boat in most conditions. The ability for the lookout to give the helmsperson the exact bearing of a target is, in my opinion, of the utmost importance. Some boaters prefer to purchase stabilized binoculars as a secondary pair. For example, a Fujinon spokesman said that some boaters buy both their 14x40 Techno-Stabi with stabilizer (or a less expensive Techno-Stabi JR) and their FMT Series 7x50 (with compass bearing finder). As another example, Canon offers the affordable 8x25 IS (roughly $299, street price) and the 10x30 IS (about $429 street price).

There are other features to consider. Steiner Commander XP series has an external lens coating they call "NANO Protection" that sheds water. When you get spray on the lenses, all you have to do is wash them off with fresh water and you're back in business, rather than having to carefully dry them over and over again during watch with special optics cloth to avoid scratching.

We've cruised for thousands of miles over many years using quality binoculars. For years before, we'd used cheap ones. Never again. Not only have quality binoculars made our lives easier, they've saved us from serious trouble time and again. 

— Published: February/March 2012

How Do They Fit Your Face?

We're all built differently, and the differences include the distance between our eyes. Good manufacturers therefore address the interpupillary distance (IPD), the amount of lens separation that allows both eyes to see a complete viewing field without overlapping or other distortion. This changes from person to person, so a range from 58 to 72 mm is typically built in. The wider the range, the more people can use the set. You adjust the set by looking at a distant target and moving the barrels on their hinge until you see one image properly. Markings on the hinge help you remember your setting.


BoatUS Magazine Is A Benefit Of BoatUS Membership

Membership Also Provides:

  • Subscription to the print version of BoatUS Magazine
  • 4% back on purchases from West Marine stores or online at
  • Discounts on fuel, transient slips, repairs and more at over 1,000 businesses
  • Deals on cruises, charters, car rentals, hotel stays and more ...
  • All For Only $24 A Year!

Join Today!