What Type Of Binoculars Do I Need? (Binocular Types Explained)

Seeing the world through a decent pair of binoculars introduces sights you never knew existed, the variations in colour of birds feathers for example. But which type of binoculars do you need? If you’re considering buying a pair of binoculars be sure to read this article first, because here you’ll find all the relevant information you’ll need to make the right choice for your needs.

How Do Binoculars Work?

Just like telescopes, binoculars make far away objects appear to be much closer to us. They do this by using a series of lenses (curved circles of glass) and prisms (pieces of glass with a number of flat sides) to change the direction light travels through them. Light enters binoculars through the objective lens, that’s the lens furthest from your eye when looking through the binoculars.

The objective lens turns the image we can see upside down, it then passes through the prisms which turn that image up the right way and reflect it towards the eyepiece and then on to our eyes. The eyepiece contains the ocular lens which enlarges the image so that we see that original image only larger.

How much larger depends on the level of magnification. For example, 8x will make the image appear to be 8 times larger than it would be with the naked eye, 10x – 10 times larger and so on.

What Are The Sizes Of Binoculars?

Binoculars come in three sizes which are determined by the diameter of the objective lens. They are;

• Compact
  These are the smallest size binoculars and are designated as any binoculars with an objective lens diameter of less than 30mm.
• Midsize
  As the name suggests, these are the middle sized binoculars and will have an objective lens diameter of between 30 to 40mm.
• Full Size
  The largest of the three sizes with an objective lens diameter size of greater than 40mm.

What Are The Types Of Binoculars?

Binoculars bring the natural world closer to us, they allow us to see distant objects as if they were directly in front of us. There are three types of binoculars available and they all do the same thing, but in a slightly different way. They are;

Porro Prism

Porro prism binoculars have offset prisms which are not in alignment with the eyepiece. The light and image travel via a bend resembling the shape of a capital N. Because of the way the prisms are set up, Porro prism binoculars look like a capital M but with a bulky midsection where the offset prisms are housed. Porro prism binoculars are large, relatively heavy, near enough impossible to fully waterproof and the prisms can easily get knocked out of alignment which will cause you headaches, eye strain and even migraine.

The good news is they’re far cheaper than comparable roof prism binoculars, have a better depth perception, a higher light transmission rate, and a wider field of view than roof prisms.

Reverse Porro Prism 

These work using similar principles to Porro prism binoculars but are far more compact than regular Porros. Another welcome feature of reverse Porros is the design makes them lighter, smaller, and also allows them to be waterproofed and fog proofed too.

The bad points that we need to mention about reverse Porros are that although they’re compact for Porro prism type binoculars, they are the largest of the compact binoculars. They also have the objective lenses positioned too close together which reduces their stereoscopic view capability which affects depth perception which is a shame as that is one of the strongest features of regular Porros.

What Are The Pros & Cons Of Porro Prism Binoculars?

Pros Of Porro Prism Binoculars	Cons Of Porro Prism Binoculars
Wide field of view	Larger
A high rate of light transmission	Heavier
Realistic 3D images	Easily misalign prisms
Better depth perception than roof prisms	Difficult to fully waterproof
Lower priced for comparable quality roof prisms

Roof Prism

Roof prism binoculars are shaped like a capital H and have both sets of lenses in alignment. This is possible due to the set up of the prisms in the roof of the lens tubes (hence the name). Roof prisms are by design narrower, more compact, much more robust and far easier to fully waterproof and fog proof than Porro prisms. However, the image they produce is between 12 to 15 % duller than Porros of a similar size.

Due to the way the prisms are positioned, they need to be aligned correctly which as it’s a precise procedure takes time and skill. This makes roof prisms more expensive to produce than Porros and naturally that extra cost is passed onto the customer. Also due to the design, the prisms send light at different rates which can cause focusing issues.

To correct this the prisms in roof prism binoculars need to be coated with a specially designed coating that prevents this out of phase image production. Once again these “P-coatings” cost more to produce and the price is passed on also. The good news is once fully aligned roof prisms will never need any attention again, unlike Porros.

What Are The Pros & Cons Of Roof Prism Binoculars?

Pros Of Roof Prism Binoculars	Cons Of Roof Prism Binoculars
Lightweight	Higher production costs
Superior magnification	More expensive purchase price
Compact (smaller to carry or pack)	Less image clarity (fractionally)
Much more robust	Narrower field of view
Easier to waterproof & fog proof

Which Type Of Binoculars Do You Need?

The type of binoculars you will need is very much dependent on which activities you are going to need them for. If, for instance, you’re going backpacking or hiking it makes sense to choose a compact pair of lightweight binoculars that won’t take up too much space or weigh too much.

There are many other scenarios where a particular type of binoculars will suit you but it’s not practical to buy different binoculars for different activities. So if you are active in various differing places and conditions it will be best to settle on a general purpose pair to cover all activities. For more information on binoculars for general use we have a page fully dedicated to binoculars for various activities.

Usage	Recommended Specs	Further Info
Bird Watching	8x – 10x magnification waterproof and fogproof	Learn more about binoculars for bird watching
Astronomy	10×50 hand held or 15×56 with a tripod	Learn more about binoculars for astronomy & stargazing
Backpacking	8×42 waterproof and fog proof	Learn more about binoculars for hiking & backpacking
Whale Watching	7×50 on a boat or 10×50 from land	Learn more about binoculars for whale watching
Opera	3x – 6x magnification (as small as possible)	Learn more about binoculars for opera
Ship Watching	7×50 from a boat 15x  – 20x or from land with a tripod	Learn more about binoculars for ship watching
Trainspotting	8×25 lightweight and compact	Learn more about binoculars for trainspotting
Archery	8x magnification – most competitions stipulate no higher than 8x	Learn more about binoculars for Archery
Cricket Matches	8×42, 10×50 waterproof	Learn more about binoculars for cricket
Football Matches	8×32 Compact and lightweight	Learn more about binoculars for football
Butterfly Watching	Specialised close focus binoculars	Learn more about binoculars for butterfly watching
Wildlife	8×32 or 8×42, waterproof, dust proof	Learn more about binoculars for wildlife
Golf	Lightweight & waterproof	Learn more about binoculars for golf
Horse Racing	Lightweight & waterproof	Learn more about binoculars for Horse racing
Plane Spotting	10x for hand held, 15x – 20x with a tripod	Learn more about binoculars for plane spotting

What Do Some Of Those Technical Terms Mean?

In the types of binoculars section, we mentioned quite a few technical terms that you might be wondering about, so let’s clear them up.

Magnification & Objective Lens

These values will be stamped actually onto the body of every pair of binoculars and will look something like 7×35, 8×42 or 10×50. The number up to and including the X indicates the magnification, so 7x means everything seen through that pair of binoculars will be 7 times larger than seen with the naked eye. 8x = 8 times larger and so on.

The numbers after the X indicate the diameter of the objective lens in millimeters. So our 10×50 binoculars have a magnification level of 10 times and an objective lens diameter of 50mm. Generally, the larger the objective lens diameter, the brighter the image will appear through the binoculars. This is because the only way light can enter the binoculars is through the objective lens.

Field Of View

The field of view (FoV) is the width of the image you can see at a set distance. For the purpose of binoculars that set distance is always 1,000 metres and in the specifications it will be set out as something like 105m@1,000m. Which means at 1,000 metres distance you’ll be able to see a width of 105 metres from left to right. Any FoV of between 105m@1,000m to 140m@1,000m is considered to be good in the world of binoculars.

3D Images

We see 3D images through binoculars only if the lenses are positioned in a particular way. Basically the further apart your eyes are, the more chance you have of seeing a 3D image. Which is why Porro prism binoculars (not reverse Porros) create a 3D or stereoscopic image. Due to the positioning of the prisms the lenses are further apart than roof prism binoculars.

This increases the 3D effect and also increases the depth perception.

Depth Perception

In general terms depth perception is the ability to see everything around us in 3D. When it comes to binoculars better depth perception allows us to realise where objects are in position to each other. For instance if we were looking at sail boats through binoculars we would be able to tell which was closest to us. The farther apart the lenses are the better perception of depth you will have.

Light Transmission

Light transmission is a very important factor in binoculars because we rely on light to illuminate the image we see through the binoculars lenses. The definition of light transmission is the movement of light through a lens and the better the light transmission the brighter and clearer the image will be seen through the lens of the binoculars.

Binocular manufacturers are optical engineers, they understand the need for superior light transmission and so they have designed prisms and optics for this purpose. Firstly, they use a blended flourite and glass prism with the least amount of imperfections as possible. This is because it’s those imperfections that cause loss of transmission of light.

BAK-4 

This is the top quality, high precision glass and fluorite combination that has been highly polished to remove as many imperfections as possible. Far smoother than glass alone could achieve. BAK-4 glass is used in the highest quality binoculars.

BK-7

This is still a combination of glass and fluorite but it has slightly more imperfections than BAK-4 glass. BK-7 glass is still high quality precision optical glass and is used in many binocular prisms.

Lens Glass

To improve light transmission even more, binocular manufacturers use special glass for the lenses too. Look for high-density (HD) glass or extra-low dispersion (ED) glass as both of these improve light transmission and help to prevent colour fringing or haloing.

Lens Coatings

Another way light transmission is improved is through the use of special coatings applied to the lenses of the binoculars. This is done to reduce loss of light due to reflection. Uncoated lenses reflect 5% of light whereas coated lenses reflect between 1 to 1.5%. There are 4 types of lens coatings for binoculars which are;

• Coated (C)This means at least one lens has at least one side coated.
• Fully Coated (FC)
  This means at least one lens has been coated on both sides.
• Multi-Coated (MC)
  This means at least one lens has been coated with multiple layers.
• Fully Multi-Coated (FMC)
  This means every piece of lens has been coated in multiple coats to decrease surface reflection. Which allows greater light transmission and produces a brighter image. It also reduces glare.

Waterproof & Fog Proof Binoculars

Virtually impossible to achieve in Porro prism binoculars (except reverse Porros) but fully achievable in roof prism binoculars, waterproofing is a very handy feature to have. Even if you never intend using your binoculars outdoors or in wet conditions. We live on a planet that is made up of over 70% water and there is often a high moisture content in the atmosphere.

This means having waterproof binoculars makes sense. It is achieved by using O-rings at any joints and purging the lens tubes of oxygen and replacing it with an inert gas. Usually nitrogen but sometimes argon. This gas is then sealed inside the tubes which then cannot escape. Which also means nothing can enter either which keeps out water, dust, mould spores and any microbial debris.

Fog Proof

As these gasses contain no moisture at all, they cannot react to sudden dramatic fluctuations in temperature and therefore will not fog up.

Other Binocular Terms

We’ve covered most of the information you’ll need to buy the binoculars best suited for your needs but it would be remiss of us to not complete the terminology.

Exit Pupil

This relates to how much light enters the binoculars to illuminate the image you see through the lens. The exit pupil should be as close to the size of the human pupil as possible to see a clearer image. The human pupil is around 2 to 4mm in daylight and dilates to around 5 to 6mm as daylight fades.

The exit pupil isn’t always quoted in the specifications for every pair of binoculars but it’s an easy calculation to do yourself. Simply divide the objective lens diameter by the magnification the result will be the exit pupil in millimeters. For instance our 10×50 binoculars from earlier have an exit pupil of 5mm because 50 ÷ 10 = 5. 

This will work every time and allows you to choose the correct size binoculars for your intended activity. Obviously if you intend using your binoculars mainly during daylight hours, the exit pupil isn’t so important, However, be aware that our pupils dilate in dull cloudy conditions too, so choose a slightly larger exit pupil than you might first consider.

Eye Relief

Eye relief is the perfect distance between the eyepiece glass and your eye to see a full clear image. Common eye relief on binoculars is between 11 to 16mm which is usually fine for most people. If you wear glasses however, you might need a pair of binoculars with long eye relief which allows space for your glasses whilst maintaining the perfect viewing point. Long eye relief is usually between 17 to 24mm.

Eye Cups

These are either constructed of soft plastic or rubber and are connected to the eyepiece to cushion your eyes when holding the binoculars up to your eyes. Usually adjustable in one of two ways. They either twist or fold up and down to accommodate the size of your face correctly.

Close Focus

This is the term for the closest you can be to an object and see it clearly. There are binoculars available nowadays with a close focus of around 2 metres (6ft 6 inches) which are ideal for watching insects, butterflies and moths.

Binocular Chassis

Below the rubber or polycarbonate covering on the binoculars (which is there to prevent minor scrapes and bumps) the actual chassis of the binoculars will be made from one of the following;

• Polycarbonate
  The majority of lower priced binoculars will have a polycarbonate chassis because it’s cheaper to produce and shape than the other two. Added to which a polycarbonate chassis is unlikely to become misshapen due to heat expansion and it’s a relatively lightweight material too. 
• Aluminium
  Aluminium is a strong, durable, corrosion resistant metal which makes it perfect for binocular chassis construction.
• Magnesium
  A magnesium chassis is usually found on the top quality binoculars. It is lighter than aluminium by about 33%, stronger, more durable and just as corrosion resistant as aluminium. If lightweight, strong binoculars are what you require then you should go for a magnesium or magnesium alloy chassis.

Interpupillary Distance (IPD)

This refers to the distance between your pupils. Everybody’s IPD is unique and this is why binoculars are hinged so you can adjust the eyepieces to fit your individual IPD.

How Much Will A Pair Of Binoculars Cost?

With so many brands, makes and models of binoculars available prices range from around £15.00 to £6,000.00. Extremes aside, you can expect to pay for a decent pair of binoculars that will last you for many years anywhere between £100.00 to £350.00. Always go for the best pair of binoculars you can afford once you decide on which type you require.

With binoculars you really do get what you pay for. That £15.00 pair will probably be OK for children to play with, but not much good for serious usage.

Warranty

Most of the top binocular manufacturers offer some form of warranty. The really good companies offer a lifetime warranty, which means as long as you own them, if anything genuinely goes wrong with them, they will repair or replace them.

Frequently Asked Questions