How to choose binoculars for birdwatching: 8x42 vs 10x42, field of view and more

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Binoculars are the one purchase that really matters in birdwatching, and the numbers printed on them tell you most of what you need to know. This guide explains those numbers and the other features worth checking, so you can compare any pair in a shop or online without relying on marketing.

What 8x42 and 10x42 mean

The two numbers are always magnification and objective lens size.

The first number (8x or 10x) is magnification. At 8x, a bird 80 metres away looks as if it were 10 metres away.
The second number (42) is the diameter of each front (objective) lens in millimetres. Bigger lenses gather more light, which helps at dawn, dusk and in woodland, but they also make the binoculars heavier.

Divide the second number by the first and you get the exit pupil, the width of the beam of light reaching your eye. An 8x42 gives about 5.25 mm, a 10x42 about 4.2 mm. A larger exit pupil gives a brighter, more forgiving image in poor light and is easier to line up with your eye.

8x or 10x?

Neither is better; they suit different birding.

8x gives a wider view, a brighter image and a steadier picture, because every hand tremor is magnified less. It is easier for finding birds quickly in trees and bushes, and it is what many people recommend for a first pair.
10x shows more detail at distance, which helps on estuaries, coasts and open country where birds are far away. The trade-off is a narrower view and more shake.

If you can, hold both in a shop and try to follow something moving. Many people find the 8x easier in practice than the specifications suggest.

Objective size: 32, 42 or 50?

32 mm pairs are smaller and lighter, good for travel and long walks, and bright enough in daylight.
42 mm is the common all-round size for birding.
50 mm and above gather more light but get heavy for carrying all day; they are more often used for astronomy or watching from one spot.

Field of view

Field of view is how wide a scene you see. It is given either in degrees or as a width at a distance: metres at 1,000 metres, or feet at 1,000 yards. A wider field makes it much easier to find a bird and follow it in flight. Two pairs with the same magnification can differ noticeably here, so compare it directly on the specification sheet.

Close focus

Close focus is the nearest distance at which the binoculars can still focus. For birds at a feeder, in a hedge, or for butterflies and dragonflies, a short close focus is very useful. Check the figure, as it varies a lot between models of the same size.

Waterproofing and fogging

Look for pairs described as waterproof, not just "weather-resistant". Waterproof binoculars are usually sealed and filled with nitrogen or argon gas, which stops the inside of the lenses fogging when you step from a warm car into cold air. For a hobby that happens outdoors in all weathers, this is worth having.

Comfort and fit

Eye relief: the distance your eye can be from the eyepiece and still see the full view. If you wear glasses, look for longer eye relief and eyecups that twist down.
Dioptre adjustment: lets you correct for a difference between your two eyes. Set it once and leave it.
Weight and balance: you will hold them up for a long time. Try them for a few minutes, not a few seconds.
Focus wheel: it should turn smoothly and be easy to reach with a finger.
Strap or harness: a harness spreads the weight across your shoulders on long days.

Optical quality

Coatings on the lenses and the type of prism affect brightness and colour. Terms such as "fully multi-coated" lenses and phase-coated roof prisms indicate better optics. Some lenses use special low-dispersion glass (often marked ED or HD) to reduce coloured fringes around bright edges. These features usually raise the price, and the jump in quality is real but smaller at each step up.

How to test a pair

Set the dioptre and focus on something detailed, such as leaves or text on a sign.
Look at the edge of the view: is it still reasonably sharp?
Look at a dark branch against a bright sky and check for coloured fringes.
Try them in shade, not just in a bright shop.
Follow something moving, then switch quickly to something close.

A modest pair you carry every time beats an excellent pair left at home because it is too heavy. Which size do you use and why? Share your experience, or ask about a specification that confuses you, in the comments.