Binocular field of view calculator

A worked example: 8 degrees

A binocular printed with an 8 degree field shows 420 ft of width at 1,000 yards. Celestron gets that figure by multiplying the angle by 52.5, so 8 x 52.5 gives 420 ft.

Audubon uses the same conversion in its birding advice. It asks for at least 6.5 degrees, and it prints that as 341 feet at 1,000 yards.

In the chart, the 8x42 size has a median view of 393 ft across 75 models. A pair with 420 ft is wider than that median, and a pair with 341 ft sits well under it.

How the numbers are worked out

Nikon defines real field of view as the angle you see without moving the binoculars. Apparent field of view is the angle of the magnified picture as it looks through the eyepiece.

Nikon follows ISO 14132-1:2002 for the apparent field and uses a tangent formula: tan ω' = Γ x tan ω, where Γ is the magnification. For an 8x pair with a 7.0 degree real field, the result is 52.1 degrees.

For meters, Nikon works out the width at 1,000 m with a tangent: 2 x 1000 m x tan (7.0 divided by 2). For 7.0 degrees that prints as 122 m. Swarovski Optik notes that makers usually state the field in meters at 1,000 meters, which is 3280 ft.

Nikon calls an apparent field wider than 60 degrees a wide field. Its older method used 65 degrees. The calculator tells you when your result passes 60 degrees.

Median view by size

The chart holds 554 binoculars. These are the seven sizes with the most models, with the median field of view and weight taken from the makers' documents.

What to do with the result

Compare your figure with the median for the size. The 8x32 size has a median of 408 ft, and the 8x30 size reaches 428 ft. At the other end, 18x56 has a median of 194 ft.

For birding, the RSPB shop suggests 7x or 8x for general and garden use and 10x for greater distances. It says a wider field helps you follow moving birds.

Audubon recommends magnifications of six, seven or eight times because they are bright and have a wide field. See the exit pupil calculator for the brightness side of that choice.

To see which models give a wide view in your size, open binoculars for birding or the full binocular chart. Field of view explained covers the idea in more depth, and best binoculars compared lists every model.