Binoculars magnification

As and when you shop for your first binoculars you will always be thrown a set of numbers and the retailer will talk about 4×21, 7×35, 8×42 and several other numbers. You will be confused as hell as I was when beginning to learn all about binoculars.

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

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.

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