8x42 vs 10x42 binoculars

View width

Across 75 models, the median 8x42 shows 393 ft at 1,000 yards, and the range runs from 290 to 477 ft. Across 87 models, the median 10x42 shows 336 ft, with a range of 288 to 400 ft.

Nikon defines real field of view as the angle you see without moving the binoculars. A wider angle helps you find and follow a moving bird, and the RSPB notes that a wider field helps with exactly that.

The same maker's pairs show the gap. The Vortex Viper HD goes from 409 ft in 8x42 to 341 ft in 10x42. The Nikon Monarch M7 goes from 435 ft to 362 ft. The Celestron Nature DX falls from 388 ft to 304 ft, the biggest drop among the pairs in the table of matched models.

Audubon says bird-worthy binoculars should show at least 6.5 degrees, which it equates to 341 ft at 1,000 yards. The median 8x42 clears that line, while the median 10x42 sits just under it.

Brightness at dusk

Exit pupil is the objective diameter divided by magnification, as Nikon, ZEISS and the RSPB all describe it. For 8x42 that works out to 5.3 mm, and for 10x42 it is 4.2 mm.

ZEISS says lower magnification gives a larger exit pupil and so a brighter image at dawn. It also says the exit pupil should be at least 4 mm for dawn use. Both sizes pass that line, but the 8x42 has more room above it.

Relative brightness works out to 27.6 for 8x42 and 17.6 for 10x42. Twilight factor goes the other way, at 18.3 for 8x42 and 20.5 for 10x42, because it rewards magnification. ZEISS treats twilight factor as a limited guide and points to exit pupil instead, so lean on the 5.3 mm and 4.2 mm figures for low light.

In daylight the gap does not show. Nikon says the eye's pupil opens about 2 mm in daylight, and that any exit pupil above about 2 mm looks bright enough then.

Steadiness and weight

The median 8x42 weighs 24.2 oz and the median 10x42 weighs 24.9 oz, so weight does not separate them. Hand shake does. Audubon says binoculars that magnify an image eight times also magnify the small movements of your hand eight times, and higher power magnifies them further.

The British Astronomical Association says anything above 10x is difficult to hold and should be mounted, and Celestron says a tripod is not required from 8x to 12x. The RSPB calls 8x or 10x the best compromise between power and practicality. Both sizes sit inside the hand-held range.

Eye relief favors 8x42 too. The median is 18 mm against 16 mm for 10x42, and among models with a printed figure, 70 of 72 reach 16 mm or more in 8x42, against 57 of 84 in 10x42. If you wear glasses, the 8x42 gives you far more choice.

Close focus is a tie, with a median of 6.6 ft for both sizes.

Who should pick which

Choose 8x42 for woodland, garden birds, dawn and dusk, and anyone who wears glasses. The RSPB suggests 8x for woodland, close range or poorer light, and Audubon says most birders prefer 7x or 8x for a bright image and a wide field.

Choose 10x42 for open country and long distances. The RSPB suggests 10x for open country or large expanses of water, and for greater distances. Its guide also notes that the 8x42 may give a brighter image than the 10x42.

If you are unsure, ZEISS says lower power is the better long-run choice when in doubt, and it puts free-hand binoculars at 7 to 10x. Browse the 8x42 models and the 10x42 models, or check your own pair with the exit pupil calculator. The best binoculars compared page lists both sizes, and binoculars for glasses wearers leans on long eye relief.