Binocular Buying Guides

How to Choose the Right Binocular Size

The question we get most is: "What magnification do I need?" It comes down to two numbers — the magnification and the objective lens diameter, written as 8x42 or 10x50.

Reading the Numbers

The first figure is how many times closer the subject appears. The second is the front lens width in millimetres. Before you buy, think about:

• How steady your hands are, because shake grows with magnification
• The light you watch in, since dawn and dusk demand a larger objective
• The weight you are willing to carry all day
• Whether you wear glasses, which makes eye relief important

Matching Specs to What You Watch

Divide the objective by the magnification to get the exit pupil. Around 5mm suits most conditions. As a rough guide:

• 8x25 to 10x25 compacts: hill walking, travel and sport. Pocket sized but dim at dusk.
• 8x42 and 10x42: general birdwatching and wildlife. The sizes most people buy.
• 10x50 and 15x70: astronomy and long range work, usually on a tripod.

Understanding Binocular Optics

Prism design and glass quality decide the brightness, the weight and how true the colours look.

Roof Prisms, Porro Prisms and Glass

Roof prism models fold the light path inside a straight barrel, so they are slim, well sealed and simple to carry. Porro prisms use the classic stepped shape, giving more depth to the image for less money. ED and HD glass cuts the colour fringing you see on high contrast edges, which matters most at 10x and above.

What About Coatings and Sealing?

Coatings matter as much as the glass itself. What to look for on the spec sheet:

• Fully multi-coated — every air-to-glass surface treated, not just the front
• Phase correction — sharpens fine detail on roof prism models
• Nitrogen or argon filled — stops the lenses fogging internally in the cold
• Waterproof rating — IPX7 survives a downpour and a brief dunking

Setting Up Your Binoculars

Most binoculars arrive with a strap, a case and rain guards. We suggest:

• Setting the barrel width until the two circles merge into one
• Closing your right eye and focusing the centre wheel on a fixed object
• Closing your left eye and adjusting the dioptre ring to match
• Rolling the eyecups down if you wear glasses, up if you do not

Several retailers include a tripod adapter — worth asking about for anything over 12x.

Maintenance Tips

To keep your binoculars performing:

• Blow grit off the lenses with a blower before any cloth touches them
• Clean the glass with a microfibre cloth and lens fluid, never a shirt
• Store them dry, because damp cases grow fungus on internal surfaces
• Keep the rain guard on the eyepieces when they hang round your neck
• Send them back to the maker for a service rather than opening the barrels