Here is my guide to help you understand how to choose binoculars for your use.

Selection based on the use

The first thing that you need to define for yourself is the fact about the potential usage of these binoculars.

Decide if you need the binoculars for

Hunting

Bird watching

Kayaking/canoeing

Boating or Marine

Hiking

Astronomy

Spectator events

All purpose

This use in turn will determine the specifications of the binoculars that you need.

Here is the overview of the main features/specification of the binoculars.

Binocular Magnification or power of the binoculars

If you read the specification of any manufacturer for a pair of binoculars it has the first thing written as NxN for example 10×50 or 7×35. The first number is the magnification which means that how much closer you would be able to see the object. The second part of the equation is that objective lens diameter

Then there are zoom binoculars which have the option of a range of magnification for example 10-22×82 will mean that magnification can be varied from 10x to 22x .

Simple guideline for magnification is

Lower the magnification the more sharp and bright is the object and vice versa

Lower the magnification the more field of view or span you will be able to see and vice versa

Bigger is the objective lens diameter the more light it will receive.

Lens coatings and Image brightness

You will see these three or four shortened versions specified as FC, MC, FMC as the lens coating nomenclature. The coating on the lens means that the lens is coated with material it will increase the light transmission through the lens to your eyes.

Guideline

More light means brighter image

FC – fully coated – Single layer of magnesium fluoride

MC – Multi-coated – Some lenses are multi-coated

FMC – All lenses will be multi-coated.

Focus

Center focus and Individual piece focus

Center focus in binoculars has a single wheel with which you can focus the binoculars rather than having to focus each eyepiece In the Individual piece focus – Each eyepiece will have to be focused individually

Close focus

It is the distance at which the objects are very sharp when viewed thorough the binoculars.

 Field of view or FOV

This means the span of area that you can see from one end to the other through your binoculars at a distance of 1000 yards.

Guideline

Large the magnification the smaller is the FOV and vice versa.

For this reason only it is important that you know the use of the binoculars. For birding binoculars it is very important that you have a large FOV as you need to spot the birds in a larger area than you would do an animal in a hunting area.

Waterproof and Fogproof

If you are using the binoculars for outdoor purpose then it is always better to go in for waterproof binoculars especially hunting, birding or boating. If you are using the binoculars only for theater of general use then may be you do not need the waterproof binoculars.

Eye relief for people who wear eyeglasses

Very important feature that you should know if you wear sunglasses. The eye relief is a must if you wear eye glasses to see properly from the binoculars.

This is the distance between your eye and the eyepiece at which you can still see the entire span of the view or the filed of view. Needed for eyeglass wearing people as they will not be able to bring their eyes much closer to the eyepiece.

Digital camera Binoculars

As the name suggests these binoculars are those which have a digital camera also in-built along with the binoculars. You should know about the following things about the specifications of the digital camera binoculars

Internal memory capacity

SD memory card slot

Instant replay function – This will mean that it has to have a LCD screen

Exit Pupil

This is calculated as the objective lens diameter divided by the magnification and it will mean that a 10×50 bino will have 5 as exit pupil. This gives an indication if image sharpness and rightness

Guideline

A 2.5mm -3mm exit pupil is good during daylight

7mm is what a human eye can easily dilate to means an exit pupil of more than 7mm is not useful

Binocular design

Porro prism or the roof prism.

Porro prism are the older design of the binoculars and the roof prism is the more recent one. As far as viewing capability is concerned there is really no difference. The porro prism has more is more easy to manufacture and in general will cost less than the rood prism.

The rood prism is more compact and trendier.

Guideline

Roof prism binoculars are more rugged as well as more trendy but expensive to make.

Binocular accessories

Neck straps – A must for the ease of carrying as well as for the reason that it will prevent them from falling or you forgetting the binoculars somewhere unattended.

Tripod  - This is required if you are using the binoculars with large objective lens diameter normally above 50mm. Till 50 mm the binoculars you will get are relatively Ok to hold in hand but above that they become too heavy to be steady in your hand.

Always visit an offline store and make sure that you feel the binoculars in hand before making a decision about binoculars to buy. 

Most of the binoculars which are good for the sporting events and these are also the best for the sports fans are the wide angle binoculars. Let us first understand what field of view is or commonly known as FOV.

What is field of view?

Now Field of view in simple language is the span of the field that you can see from the binoculars at a distance of 1000 yards.

It is measured either in feet or degrees. Please read the details about Field of view in binoculars. For example if the filed of view is 370feet then that means that you can see a from one end to other a total span of 370 feet from a distance of 1000 yards.

Sporting events means sitting in a big stadium and looking at the entire game rather than focusing on single player from a back row seat unless of course you pay top dollars and get a front row seat. Even then I bet you would need the binoculars!

This is the same as that is needed for birding binoculars where you also want to see the entire area where the birds are perched and flying.

In stark contrast is the need for the hunting binoculars where you want to see only the animal and then hunt. You will surely do not need a bigger field of view.

The best binoculars for the posting events are the Nikon Action 8×40 Ultra Wide View Binocular or the Nikon 7×50 Sports & Marine Binoculars.

On the luxury end of the binoculars you can have the Swarovski 10×25 BP Pocket binoculars or Steiner binoculars.

Zoom binoculars for the sporting events

Zoom binoculars are another type of binoculars that you can use for the sporting events. These binoculars have the option to set the zoom. The zoom will mean the power or the magnification factor. You can read in detail about the magnification in binoculars here.

Some of the best zoom binoculars for viewing a sports event are

Barska 10-30×60 Zoom binoculars or the Barska 25-125×80 Gladiator zoom binoculars

Tip: General guideline for selecting the sports binoculars is that for indoor sporting events you should choose the specifications as 6×30 or 7×25.

Higher magnification means less field of view. Sporting events need bigger field of view which will mean that you should have the binoculars which have the lower magnification say about 6 or 7.

6×30 for watching an indoor sports event

7×25 for any outdoor activities like hiking or trails

7×35 – this best as an all purpose binos for wildlife as well as hunting and birding

7×50 for celestial observation, hunting and birding

8×40 for long-distance birding and celestial observation

Spectator binoculars is another term used for the sporting events binoculars which means that you are using the binoculars as spectators. Everything applies as said above apart from the fact that when you are having a sporting event it may not be indoors and it may be in broad daylight.

For daylight viewing you need to be careful about the exit pupil in the binoculars. For daylight viewing you will need a binocular which has smaller exit pupil and that will mean an exit pupil diameter of 20-25mm.

In general during day time when the light is more than adequate then the main factor for comparing the binoculars is the magnification of the lenses. During night time the aperture size should be the main factor which is controlling the image resolution.

How does that impact you?

For a simple reason that most birding enthusiasts as well as hunters use the twilight zone that is before sunrise and after sunset for their activities.

The twilight factor on mathematical basis is calculated as square root of the diameter of the objective lens and the magnification power of the lens.

Image Credit Gustty

That means a 7×50 binos will have a “twilight factor” of 18.7 and 10×50 will have the “twilight factor” of 22.4

The twilight factor will suggest here that you will be able to see better with a 10×50 in the twilight conditions.

However nowadays with a good coating available the twilight factor is now not a major thing as before. You can have good coatings which will help you get more light in.

Before buying the binoculars you will have to make sure that you understand what all the terms which you keep hearing like the “fully coated” or “multi coated” mean.

Why does the lens need coatings?

The answer lies in the light transmission as most of the lenses if not coated can lose up to 4% of the light when it enters the lens. You will say that it is merely 4% but the fact is that that there are so many surfaces that a light transmits through that it is an established fact that the light will lose about 50% percent of its original brightness if all the lenses are uncoated.

What is the material of the lens coating?

The basic material which is coated on the lens surface is Magnesium Fluoride.

Coated – In the binocular market coated will mean that at least one air to glass surface has the antireflective coating on it.

Fully Coated – This means that lenses or air-glass surfaces are coated with the material.

Multi coated – This means that at least on lens has the up to 15 thin layers of the coating material on it.

Fully multicoated – This will mean that all lenses or air-glass surfaces will have multiple coating of the antireflection material on their surface.

Tip: Always check for the specifications before buying the binoculars. You can easily tell if the lens is coated or not as you can see a green or a purple tint on the lens.

Be careful while cleaning the lens as these chemical layers are very soft and can easily be scratched while you are busy cleaning the lens.

The new trend is ruby red coatings which are not much better than the normal coated lenses apart from the fact that these are mostly available in lower end binoculars.

How much is good eye relief?

The most important consideration is that given the eye relief you should still be able to have a good field of view. The normal eye relief is 9 to 13 mm.

Why is it important for the people who wear eyeglasses?

For people who wear eyeglasses the eyeglasses can increase the distance between your eye and the eyepiece of the binoculars. Now if the distance is more then you will see a part of the image.

Most manufacturers provide the ability to have the eyecups came down for the people who wear eyeglasses but then that is generally not a good solution. You should buy binos which are built specifically for people who wear the eyeglasses. The eye relief for these binoculars is more than 14 mm.

If you wear thick eyeglasses then always go for binoculars which are 17mm or above. A lot of people use spare eyeglasses which are of thinner lenses while viewing through the binoculars. This way you do not need to buy the special binoculars and can buy almost any binoculars available in the market.

Tips: As a general rule have your eyecup down when viewing from the eyeglasses and if you are viewing through the naked eye then get these eyecups in up position.

Always make sure to check the eye relief specification on the binoculars. A lot of manufactures do not put this specification out. You can do a manual test to get this specification. This manual test will involve holding a piece of paper behind the binoculars and viewing the binoculars against a light source. You will see a image of the source as a bright spot on the paper. The distance at which the spot will appear the brightest is the eye relief distance.

In binocular terminology it is either specified in degrees or in feet. When we measure this in feet then it is known to be liner feet at distance of 1000 yards.

How does the binocular field of view matter?

The field of view matters as you need to choose an appropriate binocular based on the kind of needs that you have. You will need a wide angle of view in case you are watching a sportsperson on the football field. You will need to have a view whereby you can see the entire field. The same holds true for the birding binoculars. For birding binoculars also this is true as you need not focus generally solely on the bird but you need to have a major focus on the entire wide area where the birds are .

How much should be the field of view (FOV) ?

Lets us talk about the measurement in length. At a distance of 1000 yards you should be able to have a field of view of about 300 to 375 feet.

Talking about the angular degrees then most of the binoculars have an angular degree field of view between 6 degrees and 7.5 degrees.

As far as the angle conversion to feet is concerned it will mean that one angle degree is equal to 52.5 feet at a distance of 1000 yards.

Image credit Geodetic.com

Again when measured in degrees most of the times you will see the specification listing the two kinds of FOV. The first kind is the apparent field of view and the second one is the real field of view. For example if the real field of view is 5 degrees then the apparent field of view will be 5 degrees multiplied by the magnification of the binoculars. So in assuming a magnification of 8 will mean that the apparent field of view is 8×5 i.e. 40 degrees.

Tip: Most of the time the wide angle binos are the best but then it is always better to take into account the need that you have for the binoculars.

How to see the exit pupils of the Binoculars?

If you hold the pair of binoculars at an arm’s length then you will see a small circle of light in each the eyepiece. This circle which you see is the exit pupil. As a thumb rule the exit pupil diameter is the obtained by dividing the aperture in millimeters by the magnification.
For example, if the specification is 7×35 for the binoculars then the exit pupil of 5mm.

What does it mean to me if the exit pupil of a binocular is less or more?

The exit pupil of the binocular should match the entrance pupil of the human eye. In normal cases the human eyes’ entrance pupil for a young adult is 5-7mm.
This is important to know because generally that determines the image’s brightness.

If your entrance pupil diameter is less than the exit pupil diameter then outer edge of the small circle of light that is coming out of the exit pupil will fall on the sides of your entrance pupil and you will see a dimmer image.

In case your entrance pupil diameter is larger than the exit pupil diameter of the eyepiece then you will be able to get all the light and will see a brighter image.

That will mean that you should make sure that the entrance pupil of your eye is equal or more than the exit pupil diameter of the eyepiece.
Young adults have about 7mm diameter in low light conditions.  As you age the entrance pupil diameter will reduce.

What are the roof prism binoculars?

Roof prism binoculars have all the three things namely the eye piece, the objective lens and the prisms all in one straight line. This helped as then the design of the roof prism binoculars was more elegant and in general there would be no such thing as the zig-zag pattern of the Porro prism binoculars.

It is easier said than done. The design was more complex internally for the roof prism binoculars and hence it was tough to manufacture. That is why the low -end binos will always be those if Porro prism system and the high -end will be roof prism binoculars.

Roof prism binoculars vs. Porro prism binoculars

Roof prism binoculars are much better looking than the Porro prism binoculars as far the design is concerned.

On the price front the Porro prism binoculars are much better than the roof prism binoculars.

In terms of light efficiency the Porro prism binoculars are much better than the roof prism ones. However now with the phase-coatings being used on the prism glass the roof prism binoculars have become equally good compared to the Porro prism binoculars

What are prisms? 

If you only used an eyepiece and then used the objective lens to see the image of the object that you are looking at then you will see the image inverted that is upside down as well as you will have the image which is reversed left for right. To correct that prisms are used in between the eyepiece and the objective lens. The prisms are used for bending the light which corrects the inverted image.

There are two types of prism systems that are used in the binoculars of today. These are the Porro prism systems and the roof prism systems. In fact there are three types and the third system is the reversed Porro prism binoculars.

The glass with which these prisms are made is known as BAK-4. Details about this later in the subsequent posts.

What are Porro prism binoculars?

Just to give you an idea look at the image below of the Porro prism below. Porro prism binos were popular in the 1960’s but now the more popular are the roof prism binoculars. They have an offset zig-zag design. This design was introduced because the light in the case of Porro prism binoculars travels in a zig-zag pattern and hence the eye piece, the prisms and the objective lens could not be in the same straight line.

With roof prisms that problem was resolved though not easily and hence generally you will see that roof prism binos are more costly than the Porro prism binos.

Porro prism binoculars are more efficient than the roof prism ones as they have better simpler mechanism to control the light.

Reversed Porro prism binoculars are very compact and can easily be the best for very compact travelling binos.

Of late however the roof prism binoculars have easily made great advances in their light management techniques and hence now they are at par with the Porro prism binoculars for light efficiency and optical experience. The way it has been achieved is via the use of the Phased coatings.

Let us first understand the basic question which is there and that is what are binoculars?

What are binoculars or binos?

Binoculars in a very simple language are the two lenses or refracting telescopes which are in some way placed together as a unit. The way they are placed together is by using a nice plastic body or a metal body.Once you see an image through these telescopes they will appear bigger than the image is in reality.

Going by the principle of optics most of binoculars use the prism to bend the light before it enters the objective lens. That leads us to two things and those are what is an objective lens and secondly what kind of prisms are used?

What is a binocular objective lens?

The lens through which you view the object is the objective lens. The greater is the size of the objective lens the more light will enter the lens and it will be better viewing. This is definitely true but the disadvantage of this is that the lens size will become bigger which will mean that the size across the diameter (measured in millimeters) will be bigger. This will mean bigger and bulkier binoculars.

In the notation that you always keep hearing like 10×42 or 8×42, the second part which is the “42″ is the size of the objective lens and the first part of the specification that is “7″ or “10″ or “8″ is the magnification. This magnification means that the object will appear 7 times closer or 8 times closer or 10 times closer.

As far as binoculars magnification and the size is concerned there are various specification available in the binoculars manufactured by various brands.

However if you need to know the best one based on you need then there is this chart which I found out at http://www.just-binoculars.com/binocular_facts.htm

As far as magnification is concerned you would have heard about the zoom binoculars. The way zoom binoculars are called so is because in zoom binoculars you can adjust the zoom or the magnification within a given range. That is if the zoom binoculars specify 8- 22 then that means that you will be able to adjust the magnification of the binoculars starting from 8 times bigger object to 22 times bigger object viewing.

What is the best hunting binoculars specification?

The magnification range between 7x and 10x is the best when it comes to hunting. Of course, since it involves hunting then you should go for the rubber armored, waterproof and fogproof binos.

For birding enthusiasts the best binoculars are the 8×42. A lot of people use the 10×42 or the 12×50 specification binoculars also. The greater the objective lens diameter it is good for birding enthusiast as you can then have greater wide area viewing.

The thumb rule is – Go for the size of the objective lens which is greater than or equal to the magnification power. This is based on the eye relief which means the viewability of the eye. This will be explained in detail in my next post about eye relief.  More magnification means more blurred image as the light is spread then over a larger area . This in turn means that you will get a blurred image.

That is why the multiplication factor of 5 is best. The 5mm – 7mm is the best “exit pupil”. Exit Pupil is the amount of light that a human eye can accept.