What do the numbers on binoculars mean? 8x42, 10x42 and 12x50

What do the numbers on binoculars mean? 8x42, 10x42 and 12x50 explained

Almost every pair of binoculars carries a designation such as 8x42, 10x42, 12x50 or 8x25. These two numbers affect much of your viewing experience: apparent closeness, brightness, steadiness, field of view, weight and comfort.

The important point is that the numbers do not tell you whether binoculars are good; they mainly help you understand which uses they suit. A 10x42 is not automatically better than an 8x42. A 12x50 is not necessarily more comfortable. A small 8x25 can be excellent, provided you understand its limitations in low light.

What 8x42 means in one sentence

In 8x42, the first number is the magnification and the second is the objective lens diameter, measured in millimetres.

• 8x means the subject appears approximately eight times closer than it does to the naked eye.
• 42 means the front lenses, called objectives, are 42 mm in diameter.

For example, an animal 800 m away seen through 8x42 binoculars has an apparent size comparable to viewing it with the naked eye from about 100 m. This is not variable zoom: standard 8x42 binoculars have a fixed 8x magnification.

The first number: magnification

Magnification often attracts the most attention. It also causes many buying mistakes. Higher magnification may seem preferable, but although it makes distant details larger, it also magnifies hand movements.

As magnification increases, keeping the image steady becomes more difficult. The field of view tends to narrow, and perceived brightness can fall in low light when objective diameter stays the same. This is why 8x and 10x remain versatile choices for handheld viewing.

8x magnification: a comfortable choice

8x binoculars are often easy to use. They provide a steady image, a generally wide field of view and relaxed viewing. They suit hiking, birdwatching, landscapes, woodland and fast-moving subjects.

If you are starting out or want an all-round pair, 8x42 is often a reassuring choice.

10x magnification: more detail, less tolerance of movement

10x binoculars bring the subject closer. They are useful for distant wildlife, mountain details, coastlines, birds of prey far overhead and open landscapes.

The trade-off is a greater need for a steady hold. The field of view is often narrower than with 8x binoculars, so locating moving subjects can take longer. For many users, 10x42 remains versatile, but it is less forgiving of hand shake.

12x and above: for more specific uses

Beyond 10x, binoculars become more demanding to hold. 12x50 can suit long-distance observation, hunting in open country, watching the sea from shore or occasional astronomy. However, the image moves more when used handheld.

For extended viewing at high magnification, a support, tripod or image-stabilised binoculars can be more comfortable.

The second number: objective lens diameter

The second number, such as 42 in 8x42, gives the diameter of the objectives. These are the large lenses at the front, facing the subject.

At the same magnification, larger objectives can collect more light. This can improve brightness and viewing comfort at dusk. Larger objectives also increase size and weight.

25 mm: compact and light

Formats such as 8x25 and 10x25 fit easily in a pocket or bag. They suit travel, performances, light outings and daytime viewing.

Their limitations are more apparent in low light: dark woodland, late afternoon, overcast conditions or twilight. Viewing can then feel less comfortable than through larger objectives.

32 mm: a balance for travelling light

8x32 and 10x32 offer a balance between compactness and viewing comfort. They are generally more comfortable than pocket binoculars while remaining lighter than comparable 42 mm models.

They make sense for long walks, lightweight travel or carrying binoculars around your neck for extended periods.

42 mm: a versatile all-round format

8x42 and 10x42 are common formats for nature observation. They balance brightness, field of view, viewing comfort and portability.

For birdwatching, hiking, daytime hunting, landscapes and general use, 42 mm is often a useful middle ground.

50 mm and above: more light, more bulk

10x50, 12x50 and 7x50 binoculars have larger objectives. They can suit low-light viewing, observation from a fixed position, some marine uses and astronomy.

They are bulkier, however. On a long walk, they may become less comfortable to carry than an 8x42 or 10x42.

Exit pupil: another useful number

The two main numbers let you calculate the exit pupil: the diameter of the beam of light leaving the eyepiece and entering your eye.

Exit pupil = objective lens diameter ÷ magnification

• 8x42: 42 ÷ 8 = 5.25 mm
• 10x42: 42 ÷ 10 = 4.2 mm
• 8x25: 25 ÷ 8 = approximately 3.1 mm
• 10x50: 50 ÷ 10 = 5 mm

A larger exit pupil generally makes viewing more forgiving, particularly as light levels fall or when the binoculars are not perfectly aligned with your eyes. It is not the only measure of optical quality, but it helps explain viewing comfort.

In daylight, your pupils are relatively small, so a small exit pupil may be sufficient. At dusk, your pupils widen, and binoculars with a larger exit pupil can become more comfortable to use.

Why two 10x42 binoculars can be very different

The numbers 10x42 provide a starting point, but they do not tell the whole story. Two binoculars with the same numbers can deliver very different experiences.

Glass quality, optical coatings, prism design, reflection control, waterproofing, ergonomics, weight, close focus and field of view all affect the result.

Do not choose solely by the highest magnification or largest objectives. The numbers indicate likely uses; optical construction determines much of the actual image quality.

Field of view: a specification worth checking

Field of view describes the width of the scene visible at a given distance, often expressed in metres at 1,000 m. A field of 130 m at 1,000 m means you can see a scene 130 m wide at that distance.

A wide field helps you locate birds, follow moving animals and scan landscapes. Within comparable ranges, an 8x42 generally has a wider field than a 10x42. Always check the specifications, as eyepiece design also matters.

Eye relief: important if you wear glasses

Eye relief is the distance your eye should sit behind the eyepiece to see the whole field of view.

Short eye relief can restrict the view when wearing glasses. Look for generous eye relief and adjustable eyecups, and check comfort for yourself if possible.

A quick guide to common binocular sizes

Which size should you choose for your activity?

For beginners and all-round use: 8x42

8x42 is often a good choice if you want one versatile pair. These binoculars balance a steady view, brightness and ease of use.

For more distant subjects: 10x42

10x42 suits open spaces, distant subjects and users with a steady hold. It brings subjects closer but needs more care to keep the image stable.

For travelling very light: 8x25 or 10x25

If compact size is your priority, pocket binoculars are practical. They can work well in daylight. For twilight or regular nature observation, 32 mm or 42 mm objectives may be more comfortable.

For twilight or stationary observation: 8x42, 10x50 or 7x50

As light falls, look for a suitable exit pupil and good optical quality. 8x42 remains useful; 10x50 or 7x50 can add viewing comfort, at the cost of weight.

For astronomy: consider weight and steadiness

10x50 binoculars are a traditional choice for looking at the night sky. Higher magnification can reveal more detail but becomes tiring without support. For longer sessions, a tripod-mounted instrument may be better suited to your subject.

Common mistakes to avoid

• Choosing the highest magnification: above 10x, hand shake becomes more noticeable.
• Looking only at lens diameter: large objectives with poor coatings do not guarantee a good image.
• Forgetting weight: bright binoculars that are too heavy may stay in your bag.
• Ignoring field of view: a narrow field makes moving subjects harder to follow.
• Not checking eye relief with glasses: this matters if you want to see the full image.

What should you remember?

The first number is magnification; the second is objective diameter. Together they help you understand likely steadiness, low-light performance, size and comfort.

• 8x42: versatility, comfort and nature observation.
• 10x42: more detail at a distance without moving to a much larger format.
• 8x25 or 10x25: travelling light and keeping binoculars close at hand.
• 10x50: low-light viewing when additional weight is acceptable.

The best choice is the format that suits how you observe: walking or stationary, daylight or dusk, woodland or open country, with or without glasses.

Frequently asked questions

What does 8x42 mean on binoculars?

It means 8x magnification and objective lenses 42 mm in diameter. This is a versatile format for nature observation.

What does 10x42 mean?

It means 10x magnification with 42 mm objectives. Subjects appear larger than through 8x42 binoculars, but the view is harder to hold steady and the field of view may be narrower.

Is 12x better than 10x?

Not always. 12x makes subjects appear larger but also magnifies movement. It is better suited to supported viewing or more distant subjects.

What is the difference between 8x42 and 10x42?

Both have 42 mm objectives. An 8x42 is generally easier to hold steady and follow subjects with, and has a larger exit pupil. A 10x42 provides a closer view of distant subjects.

Are 10x50 binoculars brighter than 10x42?

With comparable optical quality, 10x50 binoculars collect more light and have a larger exit pupil. The benefit is most relevant in low light; they are also heavier and bulkier.

Which size is suitable for hiking?

8x32, 8x42 and 10x42 are useful options, depending on whether your priority is light weight, viewing comfort or distant detail.

Explore related guides

• Binocular buying guide
• Choosing binoculars for hiking
• Choosing binoculars for birdwatching

Compare our 8x42 binoculars to find a model that suits your needs.

To compare specifications and current availability, see 8x42 binoculars, 10x42 binoculars, 12x50 binoculars.