10x42 vs 12x50 binoculars

View width and close focus

The 87 models of 10x42 in the makers' documents have a median field of view of 336 ft, and the range runs from 288 to 400 ft. The 36 models of 12x50 have a median of 277 ft, with a range of 246 to 315 ft.

Audubon says bird-worthy binoculars should have a field of at least 6.5 degrees, which it equates to 341 feet at 1,000 yards. The 10x42 median sits just under that line. The 12x50 median sits well below it.

Close focus also separates them. The 10x42 median is 6.6 ft, against 10 ft for the 12x50. The RSPB notes that close focus matters for insects, small mammals, reptiles and plants.

Brightness at dusk

Both sizes have a 4.2 mm exit pupil. Nikon, Swarovski Optik and ZEISS all give the same formula: objective diameter divided by magnification. That is 42 divided by 10 for one and 50 divided by 12 for the other.

ZEISS says dawn use calls for an exit pupil of at least 4 mm, and 4.2 mm clears that line in both. The relative brightness figure is 17.6 for the 10x42 and 17.4 for the 12x50, so the two are close.

The twilight factor is the square root of magnification times objective diameter, as Celestron and Swarovski Optik print it. It works out to 20.5 for the 10x42 and 24.5 for the 12x50. ZEISS treats that figure as a limited guide and points to exit pupil instead, and the exit pupils here are equal.

Nikon puts the eye's pupil at about 7 mm in the dark. Neither size fills that, so both leave some of the eye's opening unused at night.

Steadiness and weight

The 10x42 median weight is 24.9 oz. The 12x50 median is 29.2 oz. Both sizes lean on roof prisms most often, so the gap comes from the larger glass and body.

Audubon points out that binoculars magnify hand movement by the same factor as the image. ZEISS says free-hand binoculars typically have 7 to 10x magnification, which is where 10x42 sits and 12x50 does not.

Celestron says a tripod is not required at 8x to 12x. The British Astronomical Association is firmer, saying anything above 10x is difficult to hold and should be mounted. Plan on a tripod adapter or a harness for the 12x50 if you carry it all day.

Eye relief is level between the two. The 10x42 median is 16 mm and the 12x50 median is 15.5 mm. At 16 mm or more, which the RSPB treats as the mark for eyeglass wearers, 57 of 84 models qualify among 10x42, against 16 of 35 models among 12x50.

Same series, side by side

Vortex makes both sizes in several lines, and the pairs show the same split. The Vortex Viper HD 10x42 shows 341 ft at 24.9 oz, while the Vortex Viper HD 12x50 shows 288 ft at 28.8 oz. Both sit in the $500 to $1,000 maker list price band.

In the $200 to $500 band, the Vortex Diamondback HD 10x42 weighs 21.3 oz and focuses down to 5 ft. The Vortex Diamondback HD 12x50 weighs 28.9 oz and shows 271 ft.

The Nikon Monarch M5 pair, the 10x42 and the 12x50, break the pattern. Both show 293 ft and weigh 22.6 oz and 22.9 oz. Close focus is 8.2 ft against 14.8 ft.

Who should pick which

Pick the 10x42 if you follow moving birds, scan woodland, or want one pair for a full day on foot. The wider field and lower weight help, and the 6.6 ft median close focus suits nearby subjects. See all 10x42 models and binoculars for birding.

Pick the 12x50 if your subjects are far off and mostly still, such as hillsides, open water or the night sky. The Royal Astronomical Society names 10x50 as a usual starting size for astronomy, and 12x50 adds more power at the cost of weight. See all 12x50 models and binoculars for stargazing.

To see how the field of view figures change with power, use the field of view calculator. To compare more sizes, open the binocular size chart or the best binoculars compared.