Friday, January 6, 2012

Binocular Anatomy 101

Today's binoculars are pleasingly streamlined, user-friendly, and with their often rubber-armored bodies, are more durable than ever. With waterproofing being standard on most models, it's easy to take them along without a second thought, no matter what the weather. Yet if you're confused as to which is the eyepiece which is the eyecup, here's a handy review of The Anatomy of a Binocular.

There are precious few moving parts on a binocular: the center hinge, the eyecups, the focus knob, and the diopter. Each of these parts move in order to customize the fit to the individual user. The center hinge moves the barrels to line up perfectly with your eyes. The eyecups are the rubberized mechanism your face touches while you are looking through the binocular: eyecups extend up to give the proper distance from the eyepiece for non-eyeglass wearers (if you wear glasses, leave the eyecups down). To focus on an object, the center focus knob focuses both barrels simultaneously. The diopter fine-tunes just the right barrel, which accommodates those of us with differences in vision between our eyes. For a greater understanding on the fit of your binocular, see our video, Understanding Binoculars: Fit and Focus.

Lenses: The ocular lens is part of the eyepiece, where the magnification of the binocular is located. The accessory used to protect these lenses is called a rainguard. The larger objective lens is located in the front of the binocular. Its function is light gathering. Tethered objective lens covers reduce the risk of losing the covers in the field. However, both objective lens covers and the rainguards can usually be ordered separately.

The removable tripod adapter plug, in the front of the center hinge, conceals standard-sized 1/4" x 20 threading on which to attach a tripod adapter, in case you want to tripod-mount your binocular for hands-free viewing.

So there you have it, folks. Now go out and impress a friend with your newfound knowledge!  As always, we’ll be happy to answer any questions about your binocular.  Just give us a call at Eagle Optics.

Nina Cheney
Eagle Optics Staff
Binoculars: Bring them. See what they bring you.


  1. I find it frustrating in the descriptions of binoculars on sellers' websites when they fail to say whether the twist out eye cups stay in a locked position or not. We have one pair, I think Swift Audubon's, that pop out but when a person without glasses uses them they push right in when looked through. That is very frustrating. When buying binoculars I would want to know if the eye cups stay in position when out and in use!

  2. Dear Don,
    Twist-out eyecups are designed to easily twist up and down. They often have intermediary settings, or click-stops, but can't really be locked in the fully extended position. Still, if they can be pushed in as easily as you described, there may be something wrong with them. You may want to call the manufacturer regarding an adjustment. The phone # for Swift Authorized Repair Center is 713-529-3551.
    Thanks for your comment!

  3. Thanks for the awesome crash course in 'Binocular Anatomy 101', Nina! I had never really understood what the many different pieces and parts of a binocular were called so I am glad you shared your perspective. In my experience, binoculars have helped me to spot twice as many birds as I did before. When buying a pair of binoculars, I think that the key factors to consider are size, price, vision, durability and functionality. All of these weigh equally into finding the "perfect" pair. While it can be difficult to determine the right pair of binoculars for you, sites like this one can help! I also recommend checking out the National Audubon Society's website for more helpful advice.


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