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The Binocular Advisor

Optics Myth 4:

Bigger binoculars have a wider field of view.

Swarovski EL binoculars

REALITY - Field of view is in the design of the eyepiece.

A person might expect a bigger binocular to have a wider field of view, but it's not necessarily so. In fact, a smaller binocular can have an even wider field of view than big one. For example, in the Swarovski EL binocular line, the full-sized 10x42 (shown above, at left) has a field of view 330 feet wide at 1000 yards, while the much smaller 10x32 (above, at right) reveals a scene 360 feet wide at 1000 yards.

Although the field of view depends primarily on the binocular's eyepiece design, the magnification also has a bearing. If you're looking at two binoculars of the same model but different magnification, the lower powered one will have the wider field of view. That is one reason that many birders prefer 8-power binoculars rather than 10-power.

Vortex Viper 8x42 & 10x42

The brand new (and very good) Vortex Viper binocular illustrates the point. On the left, the 10x42 Viper has a field of view of 319 feet at 1000 yards. The 8x42 Viper, on the right, gives a more generous 347 feet field of view at 1000 yards.

It's a manufacturing challenge to provide the wide field of view that birders appreciate. The laws of eyepiece design dictate that the wider the binocular's field of view, the shorter the eye relief. Unfortunately, people who wear glasses need long eye relief in order to see the full image. By adding extra glass elements in the eyepiece, some optics makers produce binoculars with both long eye relief and a wide field of view. Such binoculars usually come at a premium price.

Field of view in degreesThe field of view is usually printed on the binocular, often expressed as an angle,such as the 7 degrees on this Nikon Premier LX.

Another way to describe the field of view is the width in feet at 1000 yards. One degree equals about 52.5 feet at 1000 yards, so a 7 degree field of view could also be described as 367.5 feet at 1000 yards). 

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Copyright 2006 Michael and Diane Porter

 

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