How to choose binoculars: the five figures that decide it

Start with the two numbers in the size

The first number is magnification and the second is the objective lens diameter in millimeters, so 8x42 magnifies eight times with 42 mm lenses, says the National Audubon Society. The most common size in the catalog is 10x42, with 87 models, followed by 8x42 with 75.

Nikon adds that larger objectives gather more light but add size and weight. The full set of pairs sits in the size chart, and the best-known models are collected in best binoculars compared.

Field of view: how much you see at once

Nikon defines real field of view as the angle seen without moving the binoculars. In feet it is the width you see at 1,000 yards. The catalog runs from 141 to 563 ft, with a median of 340 ft.

The National Audubon Society says bird-worthy binoculars should show at least 6.5 degrees, which is 341 feet at 1,000 yards. Among sizes, 8x42 has a median of 393 ft, while 10x42 has a median of 336 ft and 12x50 only 277 ft. Higher power narrows the view.

The field of view tool turns degrees into feet, and field of view explained covers the apparent angle.

Eye relief: the figure for eyeglass wearers

Eye relief is the distance between the eyepiece and your eye. The RSPB says eyeglass wearers should look for at least 16 mm. In the catalog, 337 of 529 models with a printed figure reach 16 mm or more, and the median is 16.4 mm.

Audubon says binoculars made for birders offer 15 to 20 mm. Swarovski Optik gives 14 to 19 mm for high-quality pairs and advises glasses wearers to twist the eyecups in. See binoculars for glasses wearers and the eyeglass tool.

Exit pupil: how bright the view stays

Nikon defines exit pupil as the objective diameter divided by magnification. For 8x42 that is 5.3 mm, and for 7x50 it is 7.1 mm. Nikon says the human pupil opens about 2 mm in daylight and 7 mm in the dark.

ZEISS puts the daytime pupil at 2 to 3 mm and says it seldom exceeds 4 mm in old age. So a 10x42 with a 4.2 mm exit pupil suits most daylight use, and the 5 mm or more of 8x42 and 10x50 helps at dusk. The exit pupil tool does the division.

Close focus: for butterflies and plants

Close focus is the nearest distance at which the image is sharp. The catalog median is 8.4 ft. The RSPB says it becomes important for insects, small mammals, reptiles or plants.

If you watch garden birds from a window or study butterflies, a short figure matters more than a wide field. If you scan open water from a headland, close focus barely matters.

Weight and holding steady

Audubon says binoculars that magnify an image eight times also magnify hand movement eight times. ZEISS says free-hand binoculars typically have 7 to 10x magnification. Celestron says a tripod is not required at 8x to 12x but becomes necessary at 15x and higher.

Weight rises with the objective. The median 10x25 weighs 11.1 oz and the median 8x32 weighs 18.5 oz. The median 10x50 reaches 29.3 oz, and the median 7x50 reaches 36.8 oz. See when binoculars need a tripod.

Match the figures to the use

For birds, the RSPB recommends 7x or 8x for general and garden birdwatching and 10x for greater distances. Audubon says objectives larger than 42 mm are heavier and those smaller than 30 mm are too dim for detail in poor light. That points to 8x42 or 10x42.

For stars, the Royal Astronomical Society says the sizes usually recommended are 8x40 or 10x50. The British Astronomical Association names 10x50 and 7x50 as good sizes. Browse binoculars for stargazing.

For pocket carry, Audubon says objectives under 30 mm are light and easy to carry but not bright in poor light. The RSPB describes 25 mm models as compact and for daytime use. See compact binoculars.

Compare sizes before you compare models

Settle the size first, then compare within it. The pair pages 8x42 vs 10x42 and 10x42 vs 10x50 set the figures side by side. The binocular finder filters all 554 models by the five figures, and 146 of them list ED glass.