There is now such a huge variety of binocular models on the market along with a bewildering array of specifications to choose from that it can be a daunting process choosing the right one. To aid the process of searching for the binocular best suited to your needs we have out together this useful and informative guide.
When searching for binoculars you'll soon notice each model has a series of two numbers at the end (eg: 8x25, 8x32 or 12x50). The first number is the magnification factor while the second number is the diameter of the objective lens measured in millimetres. A binocular with 8x32 in its name will magnify objects by 8 times through a 32 millimetre objective lens.
Binoculars with a higher magnification number will allow you a closer view of your subject but they will provide you with a narrower field of view with which to locate your subject initially. For binoculars with a wider field of view, then choose a model with 8x magnification or less as although the subject will not appear as close you will be able to see more. Remember also that binoculars with a more powerful magnification factor will become increasingly difficult to hold steady; 8x are relatively easy to keep steady but anything over 10x will offer a less stable image as the slightest movement in your hands will be magnified. When using higher powered binoculars it is advisable to use a binocular tripod adapter which enables many models to be mounted on a tripod for extra stability.
A common misconception with binoculars is that the field of view increases in line with objective lens size. In fact the opposite is true, at least with binoculars with for example a 30mm or 32mm objective lens which will provide a noticeably wider field of view than a 50mm objective lens. However, the larger the objective lens size, the more light gathering potential the binocular will have so for dawn or dusk observation, a 50mm or 56mm model would be preferable.
Compact binoculars are also available and typically have an objective lens size of 25mm or less. The main advantage of course is that they are light and portable meaning that you can carry them anywhere with ease. The crucial disadvantage is that unless they are of very high quality, the image will lack the brightness and clarity of larger models and the field of view will be not be as wide as a 30mm or 32mm model.
There is always a trade off in binocular specification; no one binocular will be perfect for every situation.
Once you've considered the magnification power and the size of the lens, it's time to think about what type of binocular design will suit you best.
The vast majority of binoculars fall in to two basic designs; Porro Prism and Roof Prism (see diagram below). The Roof Prism design has a straight-through appearance and has become very popular in recent years because it is more compact, usually waterproof, fog proof and filled with Nitrogen or Argon gas to keep moisture and dust out. The Porro Prism design has a more traditional shape with an angled body which means they are often bulkier, but usually less expensive. Another feature found on many modern binoculars are twist-up type eyecups, which for ease of use are better for spectacle wearers and are harder wearing compared with the old fashioned fold down rubber eyecups.
The majority of binoculars on the market use glass lenses providing better image quality compared with cheaper, plastic lenses. Similar to the glass used to improve vision, glass lens binoculars will reflect light hitting it and will typically come with a coating to prevent this. Coated optics means only some of the lens surface has been given a single-layer coating to make it anti-reflective, while fully coated means all air-to-glass surfaces have a single-layer coating. Multi-coated means one or more surfaces have anti-reflective multi-layer coatings and fully multi-coated means all air-to-glass surfaces are anti-reflective multi-layer coated.
Many of the latest binoculars employ 'ED' and 'HD' glass to enhance the image. 'ED' stands for 'Extra-low Dispersion' glass which helps reduce levels of colour fringing otherwise known as chromatic aberration. When using binoculars without ED glass it is often possible to see colour fringing especially in bright sunny conditions, particularly around the edge of pale objects. 'HD' stands for High-Definition and is essentially a marketing term for binoculars that possess 'Extra-low Dispersion' glass.