A pair of binoculars is best described as two small telescopes placed side by side. Each of them incorporates a pair of lenses that bring distant objects closer. Between the lenses, there is a pair of prisms that orient the image in the right direction. Binoculars are used for bird watching, astronomy, hunting, sporting events and concerts. Here’s how to choose binoculars that fit your needs. Know what the numbers mean.
Binoculars are often described using two numbers such as 7×35 or 10×50. The number that comes just before the “x” is the magnification factor, or power. A 7×35 lens will allow you to see things 7 times larger, while a 10×50 lens will make objects appear 10 times larger. The figure after the “x” is the objective lens diameter in millimeters. A 7×35 binocular has objective lenses that are 35 mm in diameter, while the 10×50 lens will have a diameter of 50 mm. By dividing the second number by the first, we obtain the diameter in millimeters of the ocular lens, or the light beam that will reach the eye of the user. (For both examples used, 7×35 and 10×50, the result will be 5 mm.)
Points to note
• The larger the magnification power, the smaller the field of view. While the observed object will appear larger, the field of view will be narrower, which will, therefore, make it more difficult to center the image at a specific point. If you choose binoculars with a magnification of 10x or more, consider using a tripod to stabilize your device. Basically, if you need a wide field of view, choose a lower magnification.
• The larger the lens of the binoculars, the more light it can capture; this aspect is crucial for activities in dark environments such as astronomy, or hunting at dawn and dusk. However, the larger the lenses, the heavier the binoculars will be. In general, most pairs of binoculars have a main lens 30 to 50 mm in diameter. Compact binoculars use lenses of 25 mm or less, while binoculars dedicated to astronomy have lenses with a diameters exceeding 50 mm.
• The larger the eyepiece, the greater the amount of light that reaches your eyes. The human pupil expands from 2 to 7 millimeters, according to the intensity of the light. Ideally, you should choose the size of the exit lens according to the dilation width of your own pupil.
A good number of binoculars feature glass lenses, which generally provide the best image quality but are often more expensive than plastic lenses ( a set of plastic lenses that provide the same image quality as glass lenses will also cost more.) Some glass partially reflects the light rays it captures, but this can be compensated by using binoculars with suitably processed lenses.
• The following codes describe the different glass treatments: C (Coated) means that only parts of the binocular’s lenses have been treated with a single protective layer; FC (Fully Coated) means that the entire surface of the lens has been treated with a single protective layer. MC (Multi-Coated) means that parts of the lens have been treated with multiple layers of protection; and FMC (Fully Multi-Coated) means that the entire surface of the lens has been treated with several layers of protection. Multiple layers often give better results than single layers, but raise the price of binoculars.
• Plastic lenses, which generally offer lower image quality, are more robust than glass lenses. This aspect should be considered in situations where weather resistance matters, such as hiking.
Examine the eyepieces
The eye lens should be at a comfortable distance from your eye, and slightly farther away if you wear glasses. This is called “eye relief”, and it can vary from 5 to 20 millimeters. If you wear glasses, the eye relief should be 14 to 15 millimeters or more, since the glasses are usually 9 to 13 millimeters away from the eyes.
• Many binoculars have rubber protectors around the eye lenses. This allows a better fit of the eyepiece near the eyes when using the binoculars. If you wear glasses, look for a pair of binoculars that are retractable or removable.
Test the precision setting
See how far you can adjust the accuracy in the store, and measure the distance between the binoculars and the object you are viewing.
• The binoculars are set in 2 different ways. Most binoculars have a central mechanism with a diopter corrector on the right eyepiece, to enable you to adjust the settings in the case where one of your two eyes is stronger or weaker than the other. Waterproof binoculars, however, usually have an adjustment mechanism for each side, located on each eyepiece.
• Some binoculars are not adjustable and therefore offer no opportunity to adjust the accuracy. This type of binoculars can tire your eyes if you are trying to look at something closer than the distance for which they are pre-set.
Pay attention to the design of the prisms
Most of the binoculars widen from the eyepiece to the main lens because of Ignacio Porro’s 2-pronged terrestrial rectifier they use. This makes the binoculars bulkier but allows to better reproduce the 3 dimensions of objects that are quite close. The binoculars that use the Amici roof prism are the same width all the way through, making them more compact at the cost of image quality. It is possible, however, that roof-top binoculars are equivalent in quality to Porro rectifier binoculars, but the cost will be higher.
• The cheaper binoculars use BaK-7 prisms, which tend to cut the edges of the image. The more expensive binoculars use BaK-4 prisms, which offer more brightness and a sharper, rounder image.
Compare the weights to find out what you can handle comfortably
As described above, binoculars with high magnification and very wide lenses are heavier than standard binoculars. You can solve this and stabilize your binoculars with a tripod, or use a strap that allows you to carry the binoculars around your neck. However, if you travel long distances, you should choose less powerful but lighter binoculars.
Choose between waterproof binoculars or water resistant binoculars
If you do not plan to use your binoculars in bad weather or in conditions where they are often wet, go for water-resistant binoculars. If you plan to take them on white water rafting trips, or have them with you while skiing, get a pair of waterproof binoculars.
Study the reputation and guarantees of the manufacturers
Learn about the experience of the manufacturers and their other potential optical products, as well as how they will handle your binoculars should they be damaged.