Understanding the Magnification and Objective Lens of my Binocular and Spotting Scope

Binocular size is defined by its magnification and objective, but if you are new to the hobby, what do these mean when observing. Below we have how to identify these two and how it effects your viewing.

 

Magnification

Magnification is the degree to which the object being viewed is enlarged, and is designated on binoculars as the number preceding the "x." For example, when using an 8x42 binocular, 8x represents the binocular's magnification. An 8x magnifies an image to eight times the size it would be when viewed by the normal, unaided human eye. Similarly, a 15x70 binocular magnifies an image 15 times, and so on.

The level of magnification also affects the brightness of an image: the lower the magnification, the brighter the image. In general, increasing magnification will reduce both field of view and eye relief.

 

magnification marking
Magnification is marked on many pairs of binoculars. 

Magnification Comparisons:

unadied eye 

 

Objective Lens

The objective lenses of binoculars are the front lenses. The diameter of one of these lenses, given in millimeters, will be the second number describing a particular binocular. Hence, a 7x42 binocular has an objective lens of 42mm. 

The diameter of the lens determines the light gathering ability of the instrument, with the greater light gathering ability of a larger lens translating into greater detail and image clarity. This is especially useful in low light conditions and at night.

Doubling the size of the objective lenses quadruples the light gathering ability of the binocular. For instance, a 7x50 binocular has almost twice the light gathering ability of a 7x35 binocular and four times the light gathering ability of a 7x25 binocular. This might lead you to assume that bigger is better when it comes to the diameter size of the objective lenses. In reality the size of the lens must be considered along with exit pupil and intended usage to determine the best binocular for your personal use.

 

Variety of Uses

Based on the magnification and objective lens of your binocular, below are some suggestions on what you can use your binocular for.

Magnification Level Objective Diameter
25mm - 30mm 32mm - 35mm 40mm - 42mm 50mm - 56mm 60mm 70mm 80mm 100mm
6x - 7x Hiking, Camping, Sporting Events, Concerts Birding, Travel, Sporting Events, Concerts, General Purpose Sporting Events, Astronomy
8x - 9x Hiking, Camping, Sporting Events, Concerts Birding, Travel, Sporting Events, Concerts, General Purpose Birding, Travel, General Purpose Birding, Astronomy Astronomy, Seawatch
10x - 12x Hiking, Camping, Sporting Events, Concerts Birding, Travel, Sporting Events, Concerts Birding, Travel, Hunting Birding, Astronomy, Hunting, Law Enforcement Astronomy, Seawatch Astronomy, Seawatch, Law Enforcement
15x - 16x Travel, Sporting Events, Concerts Astronomy, Hunting, Law Enforcement Astronomy, Seawatch, Law Enforcement
20x - 25x Astronomy, Seawatch, Law Enforcement Astronomy, Seawatch, Law Enforcement Astronomy, Seawatch, Law Enforcement

 

For information on Field of View, click here.