Binoculars Glossary

Get to know these terms when choosing your binos, then weigh the pros and cons. Are you watching slow moving big game, or fast moving, smaller animals? Getting a smaller, lighter binocular may force you to give up some of the advantages of a larger one and visa versa.

A binocular that is too light can be hard to keep steady, as would be too heavy of a binocular; too much coffee will do the same thing! Last, but certainly not least! Spend as much as your budget allows, you can upgrade later.

F.Y.I. Your old binos can be sold or, better yet, donated to BIRDERS’ EXCHANGE, they will take your old binos and other birding equipment (that’s still in good shape) and send it to Latin America and the Caribbean for studies being done in those countries where equipment is greatly needed and happily appreciated.


Alignment means the two barrels are seeing the same thing. They can be knocked out of alignment if they are dropped or generally misused. If your binoculars are out of alignment you will have a disturbed view and just will not get enjoyment out of the experience. To check if your binoculars are out of alignment, put them up to your eyes and sight on a horizontal plane such as a roof line or power line. Slowly pull them away from your eyes watching that line. If the line stays continuous the binos are fine but if the line breaks (one higher than the other) you have a problem. Some less expensive binoculars are not worth the repair fee so are doomed but many will have a warranty that will cover or atleast help with the repair. Call the manufacturer.


Close-focus is the distance from where you are standing to the closest object you can focus on. Some bino’s close-focus can be as far as 15 feet away so that bird in the bush right in front of you can’t be focused on, nor that hummingbird just outside your window. They are now making binoculars with a close-focus of 3 feet so you can see a butterfly if it lands on your toes!

Exit Pupil

For the best light (also called Exit Pupil), you should be able to divide the big number by the little number at least 5 times: i.e. 8×42 (42 divided by 8= 5.25) versus 8×25 (25 divided by 8= 3.125). If you like to watch nature at dawn or dusk, anything less than a 5 might make viewing a little harder; details won’t be as clear. See Objective Lens below.

Eye Relief

Eye relief is the distance between your eye and the eyepiece. If you don’t wear glasses the eye cups on your binos should be turned down, eye relief can be from 8-13mm. For those who do wear glasses, choose binos with “long eye relief” or 14-20mm, eye cups should be turned or rolled up.

Field Of View

If you want to watch fast moving animals such as birds, choose a binocular with a wider field of view (or F.O.V.). F.O.V. is the number of feet you see per 1000 feet of distance. Sometimes you have to give up good F.O.V. for a stronger power bino. 340 or more would be good, 375 or more will make you sing.

Interpupillary Distance

Make sure they fit your face, which is called Interpupillary Distance (also called IPD). Many binoculars don’t fit a person with narrow set eyes or a child’s face. If you can’t bring the two eyepieces together enough to get one viewing circle, you won’t enjoy the experience.

Lens Coatings

Check the coatings on the glass, good optics have coatings that keep the lens from reflecting light. BAK4 prism glass is good, make sure your binos are atleast that. There are numerous types of coatings, here’s an idea of how it works: “coated” just means some outer glass surfaces are coated; “fully coated” means all outer glass has been coated with atleast one layer; “fully multi-coated” is best, meaning that all outer glass has been coated with multiple layers. With poor glass, you may also see a light flare at the outer borders of your viewing field.

Objective Lens

The Objective Lens is the lens on the far end of the binocular, it is the second and larger number on the binocular (ie: 8×42). The bigger this lens is, the more light reaches your eye, the sharper and brighter the image. But keep in mind that the bigger this lens is, the more the binocular will weigh meaning more stress on your neck and possibly more shake in your view.

Power Of Lens

The first and smaller number on the binocular (ie: 8×42) is the power of the lens next to your eye. An 8 power would mean that what you are viewing is 8 times larger than what you would normally see (like a hawk!). Much more than an 8 power and you have to be a pretty steady person.