Choosing the best binocular features

Lynn Wright / 24 May 2016

We explain the essential binocular features to consider when buying the best binoculars for you.

If you’re shopping around for binoculars, it pays to know which features will make a difference to you. We guide you through the most useful binocular features.

For more on choosing the best binoculars for you, see How to buy the best binoculars.

Magnification This relates to how much larger a distant object will appear when viewed through the lens, compared to the naked eye. Magnification is listed as part of two numbers used to describe binoculars, such as 7x40. The first number, 7x, is the magnification and refers to how much closer an object will appear when viewed through the lens – in this case, seven times closer.

Objective The size of the front lens of a set of binoculars, in millimetres. This lens – or objective – is the largest and heaviest part of a binocular’s optics and has a significant impact on their weight and size. It is listed as the second number used to describe binoculars – in this case, 7x40 binoculars would have an objective size of 40mm.

Prisms There are two types of prism system used in binoculars, and they are responsible for showing the image the right way up and keeping them binoculars’ length short. Roof prism systems are less bulky as the prisms overlap, allowing the objective lenses to line up directly with the eyes. Porro prism systems are offset rather than overlap, providing a greater field of view and improved depth perception.

Coated optics Special coatings are used to increase the brightness and contrast of images, reducing eye strain.

Field of view How wide a view you see when looking through a set of binoculars. It’s measured by how many metres wide the view is at a distance of 1km, and a rule of thumb is the greater the magnification, the lower the field of view.

Eye relief Useful for spectacle wearers, eye relief refers to how far away your eyes can be positioned from the binoculars and still see the complete field of view. The greater the distance, the further away your eyes can be positioned.

Focus wheel and diopter ring A central focusing wheel that allows for each "barrel" to be focused independently to better suit individual eye strength.

Fogproof and waterproof Using a combination of O-ring seals and replacing the atmosphere inside the binoculars with nitrogen, it’s possible to fully waterproof binoculars and prevent their optics from fogging over.

Exit pupil Listed as a number that shows how bright an object will appear in low light conditions. Our pupils enlarge to 7mm, so anything less than 7mm will reduce evening and night-time viewing. Work out the exit pupil by dividing the objective size by the magnification, so a 7x40 set of binoculars would result in 5.7mm exit pupil.

Ready to choose the perfect pair of binoculars for you? Read our guide to the Five best binoculars.

The opinions expressed are those of the author and are not held by Saga unless specifically stated.

The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.