Choosing A Pair Of Binoculars
Choosing the right pair of binoculars can seem like a bit like rolling the dice and hoping for the best. What magnification is the best for my needs? Do I need weather proofing? Should I go with a porro or roof prism design? Why is one pair $50 and this other pair is $2000? Hopefully this article can keep you from just rolling the dice on a pair of binoculars. That's Anna to left by the way, with a giant pair of 15x70 Binoculars.
What the numbers mean
Binocular magnification is labeled as (magnification) X (objective lens diameter). Therefore a pair of 10x42 binoculars deliver 10x magnification and their objective lens is 42mm in diameter. When comparing binoculars, a higher first number will give greater magnification. A higher Objective lens diameter will let in more light so your view will appear brighter. Therefore a 10x50 pair will let in more light than a 10x42 pair but a 10x50 will let in more light than a 15x50 because magnification is inversely related to brightness level when all else remains equal. A rule of thumb I like to use is to first decide what magnification I need for a given task and then choose the pair that offers that magnification with the largest objective diameter I feel comfortable carrying for my viewing task. Bigger is always better in low light situations. This may be confusing but luckily simply dividing the objective lens diameter by the magnification will give us a useful number for comparisons. This number is known as the exit pupil.
In the previous paragraph I used a pair of 10x42 binoculars as an example. If we divide 42 by 10 we get an exit pupil of 4.2mm. This is the diameter the light exiting the binoculars into your eye will cover. At night when your eyes are adjusted to the darkness you probably have a pupil diameter of around 7mm. This means your eyes still have unused gathering power while using the binoculars at night. Therefore a higher exit pupil number will typically perform better for low light conditions because the binoculars will be using more of your eyes light gathering capabilities. It also explains why with some binoculars you have to move your head around to get the right view and it can appear like you are looking through a tunnel. Exit pupil diameter isn’t much of a concern during daylight viewing because your pupils constrict in light, down to a size of about 2mm.
Eye relief is the distance you need to hold the binoculars from your eyes. It can be more comfortable not having to press binoculars against your face to see the image so a longer eye relief is typically beneficial. Also if you where eyeglasses and don’t want to have to take them off you should look for binoculars with at least an eye relief number of 11mm. Here is a more detailed wiki article on eye relief if you're so inclined.
Field of View
Another spec typically divulged by binocular manufacturers is field of view. Field of view is the lateral distance from left to right you can view 1000 yards out. Higher magnifications usually result in a narrower field of view because you are more zoomed in on that 1000 yard mark.
Additional Binocular Features
Everything I’ve mentioned up until this point doesn’t really affect the cost of your binoculars. A small decent pair of 10x25 compact binoculars can you run you the same price as Celestrons large 15x70 binoculars. Surprisingly size it’s really the issue when it comes to price. The difference between a $50 pair of binoculars and a $2000 pair is in the features. The most expensive feature being high quality multi-coated glass. Below are a few features you might run into:
Porro vs roof prism
If you can hypothetically stick a straight rod all the way through the binoculars then they are of the roof prism type. These binoculars are able to be more compact because of their prism design but they also are more difficult to manufacture and therefore more expensive. Porro prism designs look more like your traditional binoculars, with the objective lenses further apart than the eye cups and are usually less expensive than their roof prismed counterparts. A third option is the reverse porro prism. This newer binocular design also allows for compact size but is typically only for smaller objective diameters since the eye cup spacing is limited by the size of the human head and the objective lens much be smaller than this diameter. Makes sense right? I've found that the roof prism design when choosing in the same brand and price range will usually be a better pair of binoculars than its porro counterpart, but not always, and certainly not among different brands. While prism type can be a decision making starting point, especially if you want the compact size and feel of roof prism binoculars, it's important to examin other features.
BK-7 and BaK-4 Prisms
Weather resistant, waterproof, and fog proof
Your cheaper binoculars might not have any of the three and your more expensive binoculars should be both waterproof and fog proof. If a pair of binoculars is fog proof we can logically deduce it must also be waterproof and weather resistant. If a pair is waterproof it must also be weather resistant. For a pair of binoculars to be fog proof it must state that they are fog proof. Weather sealed binoculars have light duty seals to prevent the internals from getting wet in the rain, they cannot take a plunge in water. Waterproof binoculars take that protection up a notch and are recommended if you’ll be around water or heavy rain. Fog proof binoculars are filled with a moister free inert gas which will not produce any condensation with sudden changes in temperature.
Lens coatings and glass quality
Visible light is comprised of a spectrum of wavelengths which the lens elements need to focus into a point. Cheap glass and cheap designs are unable to focus all wavelengths perfectly. This causes less than clear images and some amount of chromatic aberration (The blue and purple fringing around bright objects). It takes a lot of skill to manufacture great glass and this is the main reason for huge differences in binocular cost. Even great glass can suffer from lens flare and other anomalies if not coated with special lens coatings. The types of coatings, and the more elements that are coated, will also greatly affect the cost of binoculars.
Prisms can be made of two types of glass, BK-7 and Bak-4. Bak-4 prism glass is typically of a higher quality than BK-7, and allows for brigher and sharper images. That being said, will a BK-7 prism in a good name brand pair of binoculars perform worse than a cheaper brand with a Bak-4 prism? Probably not. Many of the internal features and manufacturing methods that go into making binoculars simply are not disclosed. This is where customer reviews, and testing the binoculars yourself can help the decision making process.
Something to keep in mind when choosing binoculars
While reading the specs can help you choose a pair of binoculars not everything is disclosed in the specs. Fully multi-coated optics (FMC) have no standard for what is considered Fully multi-coated, and no two company uses exactly the same process (Unless they are rebranded from the same manufacturer of course). Internal construction methods can vary widely between manufacturers and are not listed in the specs either. The internal construction methods can affect how light scatters inside the binoculars and also affect the image. As a rule of thumb I try to buy high quality name brand optics and then the best I can afford in those brands. Great brands include Leopold, Nikon, Zeiss, and higher priced Bushnell models.
It's also important to note that higher magnifications also magnify hand shake and you may need to use a tripod for anything over 10x magnification.
7x50 vs 10x50 vs 8x42 vs 10x42 vs 12x50 vs 6x30
As you can see, there are quite a few binocular magnifications available. 7x50 is often used for marine binoculars because they are going to gather the most light of all in low light conditions because they have a relatively low magnification and large objective lenses. 8x50 is also common for low light conditions, and the most common binocular size of all for multiple uses is probably 8x42. Lower magnifications than 7 are usually reserved for compact binoculars although many compact binoculars have higher magnification 8x, 10x, and even 12x, but with smaller objective lens diameters, therefore limiting most of them to daytime use.
So is any of this helping? Probably not. You still need to choose a pair of binoculars. To do that I would first ask what are you going to be using the binoculars for? Are you going to be using them with a tripod? Are you going to be using them for bird watching? I’ve found 8x to be great for birding because you have enough field of view to find a bird and at 8x there isn’t going to be much hand shake. I've spend countless hours of life knowing a bird is in front of me but not able to find them through the binoculars. This is a case of field of view being more important than mag. Once you get to 10x your hand shake becomes more apparent and it also may become difficult to find the bird in your field of view. 10x is still manageable with good handholding technique. Once you get above 10x it’s a good idea to mount your binoculars on a tripod.
Are you going to be looking at the stars with your binoculars? I actually prefer star gazing with a pair of 8x42 or 8x50 if I don’t have a tripod handy or don’t feel like lugging it out to my campsite. At 10x, 12x, 15x, and 25x the shaking is multiplied too much to get stars to stand still. At 15x, 25x, or 30x, I’d recommend an actual binocular tripod instead of a standard one. You’ll probably want a binocular tripod anyway if you’re getting into binocular astronomy so you can easily look straight up (A feat not easily accomplished with a standard tripod unless you’re a contortionist). The issue, besides comfort, is tripod weight. Regular camera tripods can wobble in the wind and this will certainly throw off your image at higher magnifications. If you are using your binoculars for astronomy I would recommend the largest objective lenses you feel comfortable using. Most of the consumer level binocular brands max out at 100mm. These are binoculars you’ll never take hiking and will always use with a tripod. I never found much use for them for looking at the stars. It’s much easier to invest in a telescope since you won’t be using the binoculars for other things anyway and telescopes give you a much closer view of the stars, moon, galaxies, etc.
So, to distill all of this information, if you'd like to use your binoculars for many things I'd get a pair of 8x42's. If binocular size isn't a concern I'd also recommend 10x50. Leopold makes a great pair of these for around $200. I'd reccomend sticking with Leopold. They make incredibly sharp optics. Check them out at Basspro: Leopold Binoculars.
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