This article is dedicated to explaining a single subject - What do the two numbers associated with binoculars mean (as an example:  an 8 X 42 binoculars)? 

1.  The First Value.  (the "8")

The first value indicates the power or the magnification of the binoculars.  An object viewed through an 8X powered binoculars will appear to be 8-times larger (closer) than if seen with the naked eye.

A point to remember before rushing to purchase a high powered binocular, as the power increases so does the magnification of your movements.  Higher powered binoculars are very hard to hold steady by hand and often require the stabilization assistance of a tripod.  That is why many marine activities, which already have the movement of water to cope with, drop to a power rating of 7X for their binoculars.

Generally the most commonly used binoculars fall into the 7X to 10X power range.

Things to consider and balance:  magnification versus steadiness.

2.  The Second Value.  (the "42")

The second value indicates the light gathering capability of the front objective lens.  The amount of light gathered by the front lens is passed through the binoculars and undergoes the magnification process.  Light is lost at various points in this process.  The light remaining relates to how bright and clear your image will appear to your eye.

The "42" in our example also means that the size of the objective lens is 42mm in diameter.  Which is fairly large for hand held binoculars.  As the size of the front objective lens increases so does the overall weight of the binoculars (a larger lens = more weight).

The more commonly used binoculars have a second value rating in the 35mm to 42mm range, with marine viewing going up to 50mm. 

Things to consider and balance:  Image clarity and brightness versus overall size and weight.

3.  Conclusion.

Binoculars in the 8X42 range generally will be better suited for more dimly lit situations, like during the early dawn or the late evening dusk.

Typically binoculars in the 8 X 25 range are adequate when viewing during the brighter mid-day hours.

Marine activities are most commonly viewed with binoculars having a rating in the 7 X 50 range.

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