To get a pair of binoculars that can really perform to your standards, you’ll have to understand binoculars. I’ve compiled here all the technical stuff about binoculars, but don’t get fazed by all the terms! Go to my binoculars guide if you want recommendations for birding, astronomy, sports or concerts watching, etc.
Power and light
If you ever wondered what the numbers “7×25” or “8×40” mean: the first number represents the power of magnification, and the second number is the diameter of the front lens. The larger the first number is, the larger the object is magnified, but it would also mean the reducing of image brightness, field of view and image stability. You may find that the image is not so steady when holding binoculars with more than 10x magnification in your hands. For these kind of binoculars, you can use a tripod.
Want to see bright and clear images in the dim light? The second number will mainly affect the brightness and sharpness of the image. Whether you are going to enjoy a starlit night or to look out for the early birds at dawn, you will need a larger exit pupil for your binoculars.
Divide the second number with the first number and you will get the exit pupil, which is the beam of light exiting the binoculars. For example, a pair of “8×40” binoculars will have a 5mm exit pupil. For normal daylight viewing, 2.5 – 4mm is good enough, but a wider exit pupil is needed for astronomy or nightlife watching.
However, I will not recommend an exit pupil larger than 7mm because it is then larger than the human eye pupil and the excess will be gone to waste. Possibly binoculars with exit pupils larger than 7mm are for marine and viewing on unsteady grounds, where a bigger exit pupil will be easier to keep centered on the eye.
But of course, the exit pupil is not the ultimate factor of image brightness. Lens coating and optical quality should also be taken into consideration.
Field of view
Field of view means the area you see in the binoculars image. It is determined by the power of magnification and eyepiece angle. If you want to watch sports or events in a stadium, where action takes place over a larger area, then you’ll need a wider field of view.
But remember that the wider field of view you have, the less magnification, that means you choose whether you want to follow the ball or you want to see your favorite sport star in a bigger sized image.
Eye Relief
Eye relief is the maximum distance you may position your eyes from the lenses and still see the entire field of view.
This is something you want to check if you wear eyeglasses, because eyeglasses will prevent you from putting your eyes as close as possible to the lenses and you don’t want to end up seeing only the center part of the image.
A 14-15mm eye relief is standard for eyeglasses wearers but if you wear thicker eyeglasses, you might want to consider binoculars with a longer 17-20mm eye relief.
Prisms
There are two kinds of prisms in binoculars – the porro prism and the roof prism. Porro prism binoculars are the older type which has offset eyepiece and lenses in zigzag shape, while roof prism binoculars are modern-looking with straight, sleeker housing.
The Porro prism is a simple and efficient technology for binoculars. It needs less cost to make than the roof prism binoculars which is complex and requires great optical precision. Nonetheless, roof prism binoculars are more popular now due to its appealing design.
 Porro prism binoculars |
 Roof prism binoculars |
Tips for those who are considering medium or low priced binoculars: porro prism binoculars will offer better performance in image quality for the money. But they’ll be bulkier and relatively less convenient to store or carry around though.
Lens coating
I’m sure that if you’re still reading this, you’re not looking for a pair of economy binoculars with plastic lenses. A pair of decent binoculars will have coating on its lenses which allow more light to go through instead of being reflected, giving you brighter images.
There are several levels of coating for binoculars:
Fully coated binoculars (FC) – all lenses of the binoculars are coated with a single layer of magnesium fluoride.
Multi-coated binoculars (MC) – some lenses of the binoculars are coated with multi layers of chemicals. This is better than single layer coating.
Fully multi-coated binoculars (FMC) – all lenses of the binoculars are multi-coated. This is the highest level of coating to give you the best and brightest images.
Fully multi-coated (FMC) binoculars are not cheap, of course, but you’ll never experience hazy images. For a less expensive but acceptable alternative, get at least multi-coated (MC) binoculars which will have some but not all lenses coated in multi-layered chemicals.
Focusing
Some people need their binoculars to focus on objects very close up, but some would like it to focus on distant things. So you might want to choose the type of focusing that suits you.
The most common type of focusing for binoculars is the center focus. Using a single wheel, it can focus on objects both very close and far away. I would recommend this for birdwatchers and insect lovers.
Another is the individual eyepiece focus, which allows you to focus each eyepiece separately, but once focused it will always stay focused from 40 yards to infinity. This is excellent for observing mid range to long range objects, but not at all suitable for seeing objects closer up. As you would guess, stargazers will prefer this.
Some binoculars also come with diopter adjustment for differences in strength between the right and left eye.
Other features
Waterproof - Waterproof binoculars prevent the inside of lenses from fogging up in the rain, and will be less susceptible to dust. You’d love this if you take your binoculars outdoors for nature trips. No more hiding them in the bag when it rains!
Rubber housing – Some binoculars are “armored” with rubber housing. They are better protected from scratches, make less noise when accidentally knocked on something, and also allow for a firmer grip. With this feature, you’ll never again scare the birds away.
Well, there might not be one single binoculars that suits your need perfectly, but I hope after reading this you’ll at least know what to look for. You can go to my Best Binoculars main page for recommendations and other binoculars guides.
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