Trying to pick out binoculars can be a confusing task! There are so many numbers, terms and types from which to choose.
It’s all about image clarity when choosing binoculars, so in this guide, I will define magnification and objective lens (written as 8x40mm, 8x being the magnification power and 40mm being the objective lens size).
I will also cover the exit pupil (measured in millimeters, or mm), as well as the coatings and prisms used in binoculars.
Reading Your Binoculars
The first thing you should consider when buying binoculars is the magnification. This will be a number followed by an “x.”
The magnification is the measurement of how much larger the object you are looking at will appear to be. It will also make the object appear that much closer to you.
8x magnification is excellent for viewing game. Nikon’s Action EX binoculars are a good example.
Keep in mind, the higher the magnification, the lower the image brightness, the less clarity of the image, and the smaller field of view.
Anything above a 10x magnification will probably be too high for hunting purposes.
These higher magnification binoculars are generally used with a tripod and are not hand-held.
The second number to look at is the objective lens or the “aperture.” The diameter of the objective lens (front lens) is measured in millimeters.
If you want binoculars for hunting or birding you’ll want to look for a binocular with a smaller magnification and a larger objective lens, like Bushnell’s 8x42mm Legend binoculars.
The objective lens determines how much light can pass through. The larger the objective lens, the more light can get through.
The disadvantage in a larger size objective lens is that the binoculars get heavier to hold and become bulkier.
More Numbering
Another important number you should consider is the field of view (F.O.V.). The field of view is the side-to-side measurement of the circular viewing field or subject area.
The smaller the field of view, the harder it will be to spot your target. Field of view is usually measured in feet, such as 330′ field of view at 1,000 yards.
In other words, if you are looking through binoculars at a target that is 1,000 yards away, you will have a 330′ wide view.
The exit pupil size is another number that is important when picking out your binoculars. The exit pupil size is related to image brightness.
The larger the exit pupil number, the brighter the image, especially in low-light situations. Note that anything larger than a 7mm exit pupil is useless.
A 2.5mm to 3mm exit pupil is fine for normal viewing. For example, Leupold’s 8x30mm Wind River Yosemite binoculars have a 3.8mm exit pupil.
If you want to view things in lower light, look for a higher exit pupil number, such as the 4.2mm exit pupil in Bushnell’s 10x42mm Legend Binoculars.
To determine the size of the exit pupil, divide the objective lens diameter by the magnification power (an 8x32mm model has an exit pupil of 4mm).
All binocular lenses will be coated. The different coatings are relative to the quality of the image.
For the best quality, look for fully multi-coated lenses, such as Bushnell’s 10x50mm Powerview Binoculars. Multi-layered/coated coatings increase light transmission and improve image quality.
Another term you will see in binocular descriptions is the type of prism used. Without a prism, you would see the image upside down!
The Porro prism is cheaper and bulkier than the roof prism. Roof prisms are smaller and allow for smoother focusing.
The prism will also be described as a BK7 or a BAK4. BAK4 is better quality, like on Alpen’s 10x42mm Apex binoculars.
Binocular Terms
In summary, here is a short glossary of terms you should remember when choosing binoculars:
- Magnification – the number that shows how much bigger the object that you are looking at will appear to be
- Objective Lens – the lenses at the front of the binoculars that allow light to pass through
- Exit Pupil – the number that is related to image brightness
- Prism – the glass used in the binoculars to make a correct, upright image
- Fully Coated – all glass surfaces that are exposed to air are coated with a single layer
- Multi-Coated – allows for the maximum amount of light to pass through
- Center Focus – uses a single wheel to focus
- Diopter Adjustment – lets you adjust focus for each eye
- Eye Relief – the maximum distance your eye can be from the eyepiece and still see the entire field of view
- Field of View – width of the sight picture
- Close Focus – the minimum distance an object must be to view it (for birding, you need at least a 4m close-focus distance.)
Conclusion: Binocular Basics
Hopefully, this guide will help you determine which binoculars are best for you and your requirements.
Choosing your binoculars and deciphering all the specifications can seem overwhelming at first, but once you understand the terms, the choice becomes more clear.
Just decide on what they will primarily be used for and find a pair that matches your needs.
What are your favorite binoculars to use? Why? Let us know in the comments section below!
I was a professional mariner. I am an amateur hunter. I used military/marine glasses (binoculars) for pelagic fishing and for navigational use. I use them for hunting.
In order to use glasses for hours at a time while scanning the horizon for sign requires high quality glasses and a porro prism system. The porro prism glasses that I buy don’t have a focus nob. Chasing focus all day will give you a headache (literally).
Military/Marine Porro Prism glasses are tuned for the individual. Once you tune (focus) for the individual, everything is crystal clear from close-in to infinity for that person. You can look at something close-in and notice an animal or sign far off with your peripheral vision because everything is crystal clear.
My friends who won’t buy Military/marine grade porro prism glasses leave their glasses at camp. My glasses are around my neck and I see twice as much as they do. And, what I see, I see very well—in detail.
Steiner has the best line of Porro prism military/marine glasses. Fog proof and waterproof. They have models that are waterproof to one atmosphere (33 feet deep).
I recommend 7×50 or 8×50. Both of my glasses are 7×50.
Don’t get a headache chasing focus. Buy high quality glasses. Buy a cheaper gun if you need to—don’t go cheap on glasses.
In reply to John, I have the Vortex 12X50 binoculars and couldn’t be happier. They are obviously somewhat larger than 8X24 but the magnification is worth it if that’s what you want. The Vortex also come with a wide neck strap and a chest harness. I also have Bushnell 10X50 and others but the Vortex are at the top.. I know, a hard decision to make, but I’m glad I did.
I find two factors are far more meaningful for everyday field use of binoculars (or other optics – I also use monoculars and spotting scopes) –
Different coatings can affect the light collected drastically, the only practical way to tell id one is better than another is to get the optics in front of your eyes and compare. Preferably in low light conditions, as that is also a factor (any optics work fine in bright sunlight). “Fully Coated” only tells a tiny part of the story
The other Is field of view (FOV), (mentioned, but not covered in depth) certainly the objective has a significant effect on this but it’s not the only factor by a long shot. Higher magnification also tends to reduce the FOV, but not all magnifications have the same FOV even with the same objectives. its also what is happening inside the optics. FOV for every day field use is critical. Spotting scopes have a very narrow field of view. GOOD general purpose binoculars need to be in excess of 400 ft at 1000 yards, and many are less than 300.
Many years ago I went through the testing process for FOV and Light gathering, My goal was also a lighter pair of binoculars, so it was not hurting my neck at the end of the day, I chose a pair of light, compact Celestron 8X binoculars years ago as the field of view was near 2X the competing binoculars, and the light capture was far and away better.
Lastly, how you carry the binoculars will affect how much you use them, The commonly provided narrow straps, and even strings, need to be tossed in the trash where they belong. A good old fashioned WIDE camera strap is much easier on your neck, and better still are the Binocular Harness straps. These cross your middle back, and have somewhat loose (adjustable) loops over your shoulders.
I have a Nikon harness strap that is pretty, but often l have to adjust them as the adjusters let the strap slip. I have made several sets using 1″ elastic strap, a leather center piece I made, some adjusters, and the hooks for the optics. (small key rings work well on the optics to allow the large hooks to work)
having them comfortable to carry, and not obtrusively large, means I often forget they are even there on my chest until I need to remove clothing! (I’ve been known to come in and start cooking a late breakfast before remembering to take them off)
Thanks for the article! I just ordered a pair of Vortex 12×50 for an upcoming elk hunt and for around the ranches longer distances. Now I’m wondering if I made the right choice. The ones I ordered are on backorder. I think I’m going to do a little more research.