A quality pair of sturdy marine binoculars is one piece of gear that plenty of boaters don’t keep aboard—but they should. Useful not only in collision avoidance and navigation, but a good pair of binoculars can also help you catch more fish and experience new wildlife you’ve never seen before.
Among the reasons folks never invest in a pair of good binoculars is because understanding their features and classifications is about as easy as launching a space rocket on your own. So, with that in mind, we’ve set out to simplify this confusing mess and make buying the right pair easy.
Millimeters and Magnification
Binoculars are classified using a pair of different numbers (e.g. 7 X 50, 8 X 50, etc.). The first number specifies the magnification, while the second number designates the diameter of the front lenses, in millimeters. So, what does this mean to you?
The first number indicates how much closer the object you are viewing will appear to you. For example, pick up and peer through a pair of 8 X 50 binoculars and whatever you’re viewing will appear eight times larger. It’s that simple.
While lots of folks think the more the magnification the better, higher power binoculars can reduce the vividness of the image. To compensate for this, binocular manufacturers have to use ever-increasing sizes of forward (objective) lenses to let in more light. The larger the objective lenses (the second number in the aforementioned specs), the more light they can let in.
With all that in mind, know that while super high-power binoculars may work well on land, they become ever more difficult to use on a boat that’s rocking back and forth in a choppy sea. That means the practical magnification limitation for binocular use on boats under about 60 feet is about 7X. Higher than that and it becomes almost impossible to keep a target in view, unless you purchase a pair of binoculars with image stabilization, which we’ll discuss shortly. This makes a pair of 7 X 50 binoculars just about right for most boaters.
Factors to Consider
Once you’ve decided on a range of binocular models based on magnification and objective lens size, there are a myriad of other features to consider. So many, in fact, that the whole selection process can, unfortunately, become quite cumbersome.
Lens Coatings: As with any lens element, about five to 10 percent of the light that enters or exits a piece of glass is reflected back. Since modern lenses—including those in binoculars—use as many as 20 different glass elements, that adds up to a lot of light reflecting around inside. This reduces clarity, brightness, and sharpness.
To cope with this phenomenon, manufacturers use special lens coatings to reduce this internal light bouncing around to less than five percent. Still, be wary of inexpensive binoculars with heavy colored coatings on the objective lens, as this can reduce light transmission.
There are four types of coating specifications. “Coated” binoculars have one or more lens surfaces coated with a single layer. “Fully coated” binoculars have lens systems with all surfaces coated with a single layer. “Multi-coated” binoculars have one or more lens surfaces coated with multiple layers, while “Fully multi-coated” lenses feature a system where all glass surfaces are treated with multiple coatings.
The more coatings involved, the better the performance and the higher the cost. Which one you choose will have a great deal to do with your budget.
Waterproofness: There’s little question that almost any gear used on a boat will get wet one way or another, whether from the humid marine environment or from direct spray or rain. A good set of waterproof marine binoculars uses O-rings and nitrogen to keep water out, and will last much longer than a cheap pair intended for bird watching. In fact, good binoculars will help get you home safely on a wet night and still be able to come back for more. Be sure to pick a model that’s fully waterproofed—and sold that way.
Compass and Rangefinder: While the advent and proliferation of inexpensive GPS systems on boats has greatly reduced the need for taking bearings or calculating your distance from an object, either a rangefinder or compass—or both—can be handy tools to have inside a pair of binoculars.
A compass will show you, in degrees, the bearing of an object, while a rangefinder reticle will help you decipher the distance between you and an object of known height. These are usually expensive options in a pair of binoculars, but worth considering if you like to have quick references to range and distance handy.
Light Transmission: The cheaper the binoculars, the less light will reach your eyes. The more expensive the binocular, the higher quality the glass used in the lenses will be, improving sharpness and clarity. High-end models allow 85 to 95 percent of the light that enters the binocular to pass all the way back to your eyes, while cheap ones can be as low as 50 percent, or less. This is another area where budget will likely dictate the sort of efficiency you end up getting in a pair of binoculars. The more efficient the light transmission, the more money the binoculars will cost… but the better the image will look.
Stabilization: Some marine binoculars offer internal stabilization that helps reduce the difficulty of focusing on objects from a pitching boat. While this is often an expensive feature, it allows higher magnification—up to 14 X magnification, in fact. Stabilized binoculars can cost two to three times as much as their un-stabilized counterparts.
Focusing Features: Some binoculars have individual focusing elements on each eyepiece to achieve focus while others have a center-focus feature that allows you to manually tune the view to suit both of your eyes. The center-focus feature tends to be easiest to use by most folks. More expensive binoculars offer auto focus, which, once set for each individual eye, provides permanent focus—even for objects at varying distances.
Field of View: This specification denotes how wide the image you see will be. The standard specification indicates width in feet when viewing an object that is 1,000 feet away. Most binoculars have a field of view in the range of 340 to 360 feet, while stabilized models with greater magnification have fields of view up to 430 feet or more.
The best course of action during your shopping should involve the help of one of the pros at your local marine supply shop. They can show you the ins and outs of the models that fit your type of boating. If a marine supply shop is not within reasonable reach, consider relying on online reviews and/or recommendations from other boaters. Either way, your eyes will thank you for the newfound reach a pair of marine binoculars can provide.
Editor’s Note: This article was originally published in May 2016, updated in December 2017 and July 2020.