Buying Guide - Binoculars
Binoculars are an optical device providing good depth effect when used with both eyes. They consist of two small telescopes fitted together side by side. The design of a telescope inverts the image to appear upside-down and back-to-front. Within a binocular, each telescope has two prisms between the eyepiece which corrects the upside-down back-to-front image.
Binoculars are used to make distant objects appear brighter and larger so you can see them more clearly.
Binoculars are used for a wide variety of hobbies and activities. Some of the most common uses include birdwatching, whale watching, boat watching, sporting events, and star gazing.
There are typically two numbers listed on any pair of binoculars separated by an “x”, for example 10x50. The number before the “x” is the magnification, which is how many times closer or larger the object appears when you observe it through the binoculars. For example, an object viewed from 200m away through a 10x magnification will appear to be about 20m away. Some magnifications will have two numbers, for example 10-30x. This means that the binoculars have a variable magnification, so you can switch from 10x to 30x and anything in between.
The number after the “x” is the size of the objective lens in millimetres. Larger objectives let more light into the binoculars, making the image brighter and clearer. Smaller objectives are lighter, more compact and typically easier to carry and hold.
What is the ideal magnification of a binocular?
The ideal magnification depends on what you intend to use the binoculars for. For most purposes, a 7x, 8x or 10x magnification is ideal, and these models tend to be smaller and easier to carry. Higher magnifications are normally used with a tripod for viewing very distant objects, such as whales, boats, and celestial objects at night. Before purchasing a pair it’s important to consider the frequency of use, the location and purpose to get the most out of your binoculars.
Why do some binoculars look very different to others?
Every pair of binoculars uses one of two broad types of prism configurations: Roof or Porro.
While the specifics are very much up for debate in the hobby community, it is generally accepted that Porro binoculars provide a greater sense of depth when viewing objects up close, so are often favoured by nature watchers. Roof prisms, however, tend to be more compact and easier to carry. In the end, if this is your first pair of binoculars then you won’t need to worry too much about which type you choose.
What is the prism glass and why does it matter?
All binoculars are constructed using glass prisms to reduce their overall size. These come in two different types of glass: BK-7 (or borosilicate) glass and BaK-4 (or barium crown) glass.
The difference between the two is that BaK-4 glass has a higher density than BK-7, which reduces the scattering of light inside the binoculars. In practice, this means that BaK-4 glass is generally clearer and crisper around the edges of your field of view and is particularly noticeable in low-light conditions.
Like with magnification, the optimum lens size depends on what you intend to use your binoculars for. Larger objective lenses let more light through the binoculars and into your eyes, while smaller objective lenses mean that your binoculars are lighter and easier to carry. Larger lenses are better for higher magnifications and low-light conditions, while smaller lenses are better for portability.
When you look at a binocular’s specifications, it will list its exit pupil, which is the small disc of light that is projected into your eyes and is directly correlated to the objective lens size. As a rule of thumb, if you want to use your binoculars during the day, then an exit pupil of 2-4mm is ideal. If you want to use your binoculars in low-light conditions, then an exit pupil of 4-8mm is preferable.
All binoculars have at least some coatings on some of the lenses that are designed to reduce reflections and therefore increase the brightness and clarity.
If binoculars have fully-coated optics, it means that all air-to-glass surfaces have been coated. Multi-coated optics means that one or more of the lenses has coatings applied with multiple films. This improves the brightness and contrast of the image when compared to fully-coated optics.
Fully multi-coated optics means that all air-to-glass surfaces have received multiple layers of film, which again improves the brightness and contrast of the image compared to multi-coated optics.
We recommend purchasing binoculars with the highest coating rating within your budget, as this will provide the best quality image and give you the most out of your binoculars.
Small compact binoculars are best for bird watching. The ideal magnification would be 10x, with an objective lens 25-40mm diameter. Choose a lightweight model that will enable you to track moving targets easily. Certain coatings and lens types may make the image clearer, especially when observing wildlife from a far.
Similar to bird and wildlife watching, compact binoculars are ideal for recreational uses such as sport, boating and racing. Magnification of 8x or 10x is ideal. An objective lens 21-25mm diameter will allow sufficient light for clear images. Watching fast paced sports require a focus free or self-focusing binocular to enhance the experience. You should consider the weight of the binoculars if you will be using them for a prolonged time. A number of waterproof models feature an o-ring seal and have been nitrogen purged for reliable fog proof and water performance, making them great options for boating or fishing.
A larger objective lens is a helpful feature in low light or for long distance. Look for an objective lens of 40+.
If you are looking for a mid-size pair of binoculars, consider purchasing one with a zoom to enable to you magnify the image further. When purchasing a large binocular, we recommended considering a tripod adaptor and tripod, for stability and weight reduction. Another consideration may be a harness if you’re on the go.
Compact binoculars are the most commonly used as they are convenient, lightweight and very affordable. They suit a variety of activities and are a great choice for children as they are low weight.
Put simply, a monocular is half a binocular. They are used to view objects in the distance making them appear closer whilst only using only one eye.
They are best suited for hiking where you only have one arm free and want quick access to view distant wildlife, golfing and when wide field of view is required. They are also suitable for perspective views using both eyes open for the widest field of view. Most night vision instruments are also monocular, these are slightly larger and heavier with built in true night vision technology.
Any compact binoculars are suitable for children. Magnification of 6x or 8x is ideal. Choose a light weight and small pair of binoculars with a strap, this will protect the binoculars from accidental falls.
Larger high-powered binoculars typically have the ability to mount onto a tripod for prolonged viewing sessions and increased stability. In this instance a tripod adapter and tripod can be a very useful accessory.