Binoculars are basically two small telescopes paired with each other, each consisting of a pair of lenses that approach distant objects and two prisms, which straighten the image that would otherwise be upside down. Binoculars can be used in hunting, bird watching, astronomy or to follow events and concerts. Here's how you can choose the binoculars that best suit your needs.
Steps
Step 1. Interpret the meaning of the numbers
When referring to binoculars, two numbers are used, such as 7x35 or 10x50. The first number indicates the magnification factor (power); a 7x35 binocular will make objects appear 7 times closer, while a 10x50 binoculars will make objects appear 10 times closer. The second number indicates the diameter of the main lenses (objective lenses) expressed in millimeters; 7x35 binoculars have objective lenses with a diameter of 35 millimeters, while in 10x50 binoculars the objective lenses have a diameter of 50 millimeters. If we divide the second number by the first, we obtain the value of the "exit pupil", that is the diameter of the light beam reaching the eye, also expressed in millimeters. In the previous examples, 35 divided by 7 and 50 divided by 10 gives the same result of 5 millimeters.
- The higher the magnification, the less bright the image, and even though the image you see is larger, the angle of view is narrower, which will make it more difficult for you to hold your subject in the frame. If you choose binoculars with a magnification factor of 10x or greater, get a pair that has a tripod mount so that you can mount it on one of them and give it stability when needed. If you need a wider angle of view, choose a smaller zoom factor.
- The larger the diameter of the binoculars' lenses, the more light they will be able to capture, an important feature in the case of activities in low light conditions, such as in astronomy or when you go hunting at dusk or twilight. However, the larger the lenses, the heavier the binoculars. Binoculars usually have lenses with a diameter between 30 and 50 millimeters; Compact binoculars have lenses that are 25mm in diameter or less, and binoculars used in astronomy have lenses that are larger than 50mm in diameter.
- The larger the exit pupil, the more light will get to your eye. The human eye dilates from 2 to 7 millimeters, depending on the amount of light available. Ideally, you should opt for an exit pupil value that matches your pupil dilation.
Step 2. Consider the lenses
Most binoculars have glass lenses, which generally produce better quality images, but cost more than plastic ones (although it must be said that plastic lenses that produce images of the same quality as glass ones have a cost. greater). Glass has the property of reflecting part of the light that hits it, but this phenomenon is attenuated with an adequate anti-reflective treatment.
- The anti-reflective coatings are coded as follows: C means that only some surfaces of the lenses have been coated with a single anti-reflective layer; FC means that all lenses have been coated; MC means that only some lens surfaces have been coated with multiple layers; FMC means that all the lenses have been coated with multiple layers. Treatments with multiple layers of anti-reflective coating are generally superior to those with a single layer, but add to the cost of binoculars.
- Plastic lenses, which usually generate lower quality images, are stronger than glass ones, and should be considered in cases where resistance to external factors is important, such as when carrying binoculars while climbing a Mountain.
Step 3. Evaluate the eyepieces
The eyepiece lenses should be at a comfortable distance from your eyes, and if you use glasses the distance should be even greater. This distance is called "extension of the posterior field of view of the eyepiece" (eye relief), and normally varies between 5 and 20 millimeters. If you wear glasses, you will need to choose binoculars that have an eye relief of 14-15mm or more, as most glasses fit 9-13mm from the eye.
Many binoculars include rubber eyecups around the eyepieces to help you rest the eyepieces on your eyes. If you wear glasses, look for binoculars that have soft or removable shells
Step 4. Test the focus distance
Check the minimum focusing distance in the shop and measure the distance that separates you from the framed object.
- Binoculars can focus in two ways: most of them have a central ring mechanism as well as a diopter corrector in case one eye sees better or worse than the other. However, waterproof binoculars usually have a focus ring for each lens.
- Some binoculars are "focus-free", without the ability to adjust the focus in any way. These binoculars can cause eye strain if you try to focus on something that is closer than the predetermined distance.
Step 5. Pay attention to the arrangement of the prisms
Most binoculars have objective lenses that are more distant from each other than eyepieces, because they use Porro prisms. This arrangement of the prisms makes the binoculars larger, but gives more three-dimensionality to the closest objects. Binoculars that use roof prisms have the objective lenses in line with the eyepieces, making the binoculars more compact, but the quality is at the expense. However, roof prism binoculars can be structured to give images of the same quality as Porro prisms, but at a higher cost.
Cheaper binoculars use BK-7 prisms, which tend to warp one side of the image, making it square, while more expensive binoculars use BAK-4 prisms, which give brighter, sharper and more rounded images
Step 6. Determine how heavy binoculars can be so that you can handle them safely
As already mentioned, binoculars with a higher magnification factor and with larger lenses weigh more than standard ones. You can compensate for the weight of the binoculars and make them more stable by mounting them on a tripod or using a strap that allows you to hang them around your neck, but if you have to go on long hikes you may be satisfied with a less powerful but lighter and more manageable binoculars.
Step 7. Consider choosing waterproof (waterproof) or water-resistant binoculars
If you don't plan to use it often in bad weather or humid conditions, you can choose water resistant binoculars. If, on the other hand, you could take it with you while rafting the rapids or going skiing, choose the waterproof ones.
Step 8. Find out about the manufacturer's reputation and warranty
Consider how long the manufacturer has been making binoculars and what other optical products they make, if any, and how they handle the warranty when the binoculars need service.
Advice
- Some binoculars have variable zoom factor, allowing you to choose whether you want to frame the entire scene or zoom in on a particular detail. However, if you increase the zoom factor, the field of view narrows, and it will be more difficult to keep the image in focus.
- Some particularly expensive and very high magnification binoculars include image stabilizers to help keep the image in focus. Generally these binoculars cost several hundred euros, up to over a thousand.
