How To Choose Binoculars For Sea & Ocean Viewing (Best UK Guide)

How To Choose Binoculars For Sea & Ocean Viewing (Best UK Guide)

There’s nothing more entertaining, or exciting than a day at the beach. But if you want to gaze out to sea and watch the boats or sea life in greater detail, you’ll need a good quality pair of binoculars. Imagine being able to watch some rare Atlantic puffins close up, or maybe whale watching interests you, or you might just want a closer view of those magnificent ocean going ships that cruise past just on the edge of the horizon.

With the right pair of binoculars you’ll be able to open up a world that you’ve always dreamed of but never thought possible. Whether you’re standing on the beach or on top of some of the sea cliffs that edge vast areas of the British coastline, a good pair of binoculars will help you get the clearest views of anything in the water or in the skies above you too.

Whatever purpose you plan to use your optical equipment for, you’ll need to strike the perfect balance between magnification and objective lens diameter. The highest possible magnification won’t necessarily offer you the best, clearest views, but the correct size objective lens diameter will.

Magnification & Objective Lens Diameter For Sea & Ocean Viewing

When it comes to magnification on binoculars the uninitiated often think more is best, but that’s only true up to a point. The thing is anything you see through a magnified binocular lens is, well, magnified. Sometimes that over magnification can cause issues that our brains can’t keep up with. 

Part of the physiology of humans makes us shake ever so slightly when holding a reasonably heavy object up in front of our face. It’s natural and all perfectly normal and we don’t need to get concerned about it (usually), but when that shake is exaggerated by high magnification, the image we’re trying to look at becomes blurry and hard to distinguish. This happens with all magnification sizes above 10x when held by the hands.

So on land the highest recommended magnification level for hand held binoculars is 10x, any higher and you’ll need a tripod or stand to support the binoculars to prevent that shake we just spoke about. Notice we said “on land” that’s because if you happen to be at sea, on a boat or sailing vessel, the image will appear too shaky at even lower magnification levels. That’s why for use from any ocean going vessel we recommend a magnification of no higher than 7x.

If you are staying on the beach (or cliff head) and want to see boats etc in much more detail you might want to consider 12x or even 15x, but remember due to the shaky image, you’ll need a tripod. Which will limit your movement and of course the higher magnification can affect the exit pupil size (more below).

7x is still pretty powerful, it allows you to see objects 7 times larger through the lens of the binoculars than would be possible with the naked eye. But the magnification is only half of the story, in many ways the diameter of the objective lens is far more important than the level of magnification.

Why Is The Objective Lens Diameter Important For Sea & Ocean Viewing Binoculars?

The objective lens (the lens closest to the object you’re looking at) is the only entry point in binoculars for light. The light that gathers inside the binoculars is what makes the image you’re looking at bright enough to see. Unless there’s enough light entering the binoculars, you won’t be able to see the subject matter clearly.

The diameter of the objective lens also tells us the size of the binoculars too. There are three sizes of binoculars;

  • Compact
    These are the smallest size of binoculars and are any binoculars with an objective lens diameter of below 30mm.
  • Mid Size
    These are the intermediary size binoculars and have an objective lens diameter of between 30 to 40mm.
  • Full Size
    These are the largest size of binoculars and have an objective lens diameter of higher than 40mm

With modern technological advancements, even full size binoculars are not always massively heavy but the larger the objective lens diameter, the heavier the binoculars will be.

How To Tell The Binoculars Size At A Glance

Actually stamped onto the body of the binoculars you will see a series of numbers split with an X, 7×50 for example. This tells us the size of the binoculars at a glance, the first numbers followed by the X tells us the magnification, in this case 7 times (the X represents times). Followed by the diameter of the objective lens in millimeters, in this case 50mm.

As these binoculars have an objective lens diameter of more than 40 (50) we can tell they are full size binoculars.

 What Else Do These Numbers Tell Us?

Not only do those numbers tell us the overall size of the binoculars, the diameter of the objective lens and magnification level, from these numbers we can determine the exit pupil size. Just by dividing the objective lens diameter by the magnification level, will tell us the exit pupil size of the binoculars. 50÷7=7.14 so this particular pair of binoculars has an exit pupil of 7.14mm.

What Is An Exit Pupil And Why Is It Important?

The exit pupil is the size of the light beam that leaves the binoculars and hits our eyes when looking through the binoculars. It is important because the more light that leaves the binoculars and passes to our eyes, the brighter, and clearer the image will be. 

This is especially important when looking out to sea because on overcast days particularly, the sea looks quite dark and so there’s not too much reflective light. So the more light that reaches our eyes the clearer and brighter the image will be.

The human pupil at the age of 30 is 7mm on average, the pupil size decreases every decade by one mm so at age 40 the pupil will be 6mm and so on. Now we know how important it is to get binoculars with an exit pupil equal to, or greater than our own, we can easily find a pair that will give us the best chance of finding something interesting to look at while at sea or on the beach.

Other Important Factors For Sea & Ocean Viewing Binoculars

So far we’ve looked at the magnification, objective lens diameter, the exit pupil, how to find them

And why they’re so important when it comes to choosing the perfect binoculars for  sea & ocean viewing. But that’s only part of the story, to make the most of your ocean viewing experience there are many more important factors that are absolutely necessary to get right. Let’s get straight into it.

The Field Of View

The field of view (FoV) is the area you can see through the binocular lens from side to side while still looking straight ahead. It’s quoted in one of two ways in the binocular specs, either as a degree (angular FoV) or as so many metres per 1,000 metres (linear FoV). Anywhere between 6° and 8° or 105m per 1,000m to 140m per 1,000m is acceptable for binoculars for general usage, but for sea & ocean viewing we would recommend the widest FoV you can find (and your budget will stretch too).

Eye Relief

The eye relief is that perfect spot between the binocular lens and your eye to see the full field of view. Quoted in the specs in mm, the average eye relief is between 12 to 16mm. If you have to wear glasses, you’ll probably need what’s known as long eye relief which is anywhere between 16 to 24mm. You can adjust the eyecups to make some extra eye relief but possibly not enough for all styles of glasses.


These are the soft plastic or rubber edges on the eyepieces of binoculars. They are designed to keep your face around the eyes comfortable whilst looking through the binocular lenses. To adjust the eyecups they either twist up and down or roll up and down depending on the brand. 

Which Type Of Binoculars Are Best For Sea & Ocean Viewing?

There are two types of binoculars and they both have good and bad points, we don’t want to bore you with a load of unnecessary information nor baffle you with too much technical talk, so here’s a quick run down of both types.

Roof Prism Binoculars

These look like a capital H, two straight tubes linked by the central focussing knob. The prisms are situated within the roof of the lens tubes (hence the name) which saves space, and keeps the weight down too. Due to the shape and design roof prisms are easier to waterproof but that precision engineering does come at a price, in excess of comparable Porro prisms.

Porro Prism Binoculars

These look like a capital M and have two offset prisms for each lens. The bulky size and shape of Porro prism binoculars is due to the housing of the prisms which makes them larger, heavier, bulkier, and far more difficult to waterproof than roof prisms. Porros are considerably cheaper to manufacture than roof prisms but there is a distinct possibility of misaligning the prisms which can cause eye strain and headaches.

Waterproof Binoculars

If you’re staying on dry land, you might think waterproofing an unnecessary measure for your binoculars. But we live in the UK where rain is a constant threat even during Summer months. Once any water gets into your binoculars they will never be the same again, so in our opinion waterproofing is an absolute must.

There’s an industry code set up to make the degrees of waterproofing easier to understand (it’s not) so to clarify it for you, as long as the binoculars have an IPX code of 6 or more they will not allow rain water in at all. IPX7 refers to how long they could remain under 1 metre of water without letting in water and so on.

Fog Proof Binoculars

It’s very easy for sudden temperature changes to occur in Great Britain, if there is a sudden drop (or raise) in temperature, binocular lenses could fog up. Fog proofing removes all of the air from the binocular lens tubes and replaces it with either nitrogen or argon. As neither of these contain any moisture, they cannot react to changes in temperature and so do not fog up.

Dust Proof Binoculars

As an added bonus of the gas being sealed into the lens tubes, nothing else can enter, very handy on a beach. Minute particles of sand and dust are continuously blowing around in the sea breezes, which could get into the binocular lens tubes and cause issues with the viewing process. If your binoculars are fog proof, this can’t happen.

Protective Outer Shell

Whenever you use binoculars there’s a chance you could drop them, this might not damage them but it could. Buying binoculars with a protective coating, like rubber or polycarbonate will help to prevent any accidental damage from happening. Most of the quality binocular manufacturers produce binoculars coated for protection.

Maximum Light Transmission Glass

We said earlier about the need for extra light with binoculars for beach, sea and ocean use. The actual glass that makes the prisms and lenses makes a huge difference in light transmission. The best glass for prisms with the least number of imperfections is BAK4 glass, this is used in high end binoculars. The next grade down is BK7 glass which is still high quality precision optical glass but it has slightly more imperfections than BAK4 glass.

Then there’s ED glass, this extra low dispersion glass provides clearer, brighter images, with no colour fringing. It’s used for binocular lenses. Other inferior quality glass can cause a haloing effect around the image which makes it difficult to see clearly especially if that object is surrounded by light reflecting seawater.

Lens Coatings

Having the binocular lenses fully coated is also very important when it comes to binoculars for sea and ocean viewing. There are many types of binocular lens coatings but for sea and ocean viewing, we recommend fully multi-coated lenses (FMC). This means that every lens, inside and out will have been coated in multiple layers to prevent glare and improve the light transmission, contrast and brightness. 

Having FMC lenses won’t automatically make the images you see through your binoculars better, it’s only when used with BAK4 prisms and ED glass, and not forgetting the correct objective lens diameter and magnification size too.

What Are The Benefits Of Sea & Ocean Viewing?

There are a whole host of benefits from sea watching and according to one university [1] coastal living improves mental health. Even if you don’t live by the coast in the UK you’re never more than 70 miles [2] away from the sea. Here are a few of the benefits you will reap by visiting the coast.

  • Sea Air Is Good For Your Lungs
    According to the Lung Health Institute [3] breathing in sea air is beneficial for the lungs. It is reported to; reduce coughing, thin mucus, decrease sinus pressure, and improve lung function.
  • The Beach Relieves Stress
    The sound of the waves, the feeling of sand on your feet and the warmth of the sun can help to relieve stress levels[4]. According to the University of New Hampshire.
  • Visiting The Beach Can Improve Your Sleeping Habits
    According to the same study, there are 3 things that affect your ability to sleep, they are stress, not being tired, and an imbalance in hormones. The beach can offer stress relief, hormone regulation, and allow you to exercise freely whilst walking.
  • Sea Air Contains More Oxygen
    According to the National Ocean Service[5], between 50 to 80% of the earth’s oxygen comes from the sea. The closer to the ocean you are, the more oxygen you are breathing into your body.
  • Sea Water Is Good For Your Skin
    A research into the healing effects of seawater on the skin by the USA National Library of Medicine[6] found that sea water contains magnesium which is known to enhance skin hydration, and reduce dry skin inflammation.

So get down to a beach, improve your health and enjoy some great viewing with your new sea & ocean viewing binoculars.

Frequently Asked Questions

What are the best binoculars for looking out to sea?

The best size binoculars for looking out to sea will depend on whether you are using hand held or tripod supported binoculars. Hand held binoculars with a magnification of up to 10x will be good but for the best lighting and exit pupil we would recommend 7×50. For tripod supported binoculars maybe 15x mag will be better.

What are 7×50 binoculars good for?

7×50 binoculars are traditionally the size of marine binoculars. They will be great for low light conditions too due to the exit pupil size of 7.14mm.