What the Numbers Mean
Every binocular has two numbers, like 10x42. The first is the magnification: 10x makes things look 10 times closer. The second is the objective lens diameter in millimeters: 42 mm front lenses. Together they decide how much detail you see, how bright the image is, how wide the view is, and how steady it feels.
What Is Field of View?
Field of view (FOV) is how wide an area you see through the binocular. Makers give it in one of three ways:
- Feet at 1,000 yards — common in the US (for example, 330 ft at 1,000 yds).
- Meters at 1,000 meters — common in Europe.
- Degrees — the "true" field. One degree is about 52 feet at 1,000 yards, or about 17.5 m at 1,000 m.
A wider field makes it easier to find a bird or animal, follow moving targets, and scan big areas quickly.
The Trade-Off: More Power, Narrower View
With similar designs, higher magnification shows a narrower area. A good 8x42 often shows around 400 ft at 1,000 yards; a 10x42 around 330 ft; a 12x50 less again. Premium designs push these numbers wider — that's a big part of what you pay for in glass like the Swarovski NL Pure — but the rule holds: more power means a smaller slice of the scene.
Three More Things Magnification Changes
Steadiness
Magnification also magnifies hand shake. Most people can hold 8x and 10x steady; at 12x the shake becomes noticeable; at 15x and above a tripod or rest makes a huge difference.
Brightness (exit pupil)
Divide the objective size by the magnification to get the exit pupil — the beam of light reaching your eye. An 8x42 gives 5.25 mm, a 10x42 4.2 mm, a 10x32 3.2 mm. In daylight anything over about 3 mm looks bright; at dawn and dusk, a bigger exit pupil looks noticeably brighter.
Depth of field and close focus
Lower power keeps more of the scene in focus at once and usually focuses closer — handy for birds at a feeder or butterflies at a few feet.
Apparent Field of View
You may also see "apparent field of view" — how wide the view feels to your eye. It's roughly the true field in degrees multiplied by the magnification. Around 60° or more feels wide and immersive; under about 50° can feel like looking down a tube.
Eye Relief for Glasses Wearers
Wide-field designs sometimes have shorter eye relief. If you wear glasses, look for roughly 15 mm or more and twist-down eyecups, so you can see the whole field with your glasses on.
Which Magnification Should You Choose?
- Birding: 8x32 or 8x42 — wide, steady and close-focusing. See Optics for Birding.
- Hunting in timber: 8x42.
- Western / open-country hunting: 10x42 handheld, plus 15x on a tripod. See Best Binoculars for Elk & Western Hunting.
- Long-range glassing: 12x50 to 15x56, or a spotting scope.
- Travel and hiking: compact 8x25 or 10x25 such as the Swarovski CL Pocket.
Not sure? For most people, a quality 8x42 or 10x42 is the safest first binocular — wide enough to find things, powerful enough to see detail, and steady by hand.