Adjusting Your Binoculars

Adapted from Allen Turner and Judy Boyd


First, let us look at your binoculars. They are really two telescopes connected by a hinge. Near the hinge is a focusing knob which elongates or shortens the binoculars to bring your target into focus. Each telescope has an objective lens which is the large lens closer to your target, and an ocular lens which is located closer to your eye. On the ocular lenses is an eye relief cup that keeps the lens away from the surface of your eye. If you wear glasses, the eye relief cup is best pushed, or folded, in. On one ocular lens is also a diopter ring used to accommodate the difference in visual acuity between your eyes.


There are four variables to adjust to get the most out of your binoculars:


  1. Eye relief is the distance from the eyepiece (ocular lens) to the surface of your eye. If you wear glasses, see that the eyecups or rings on the ocular are pushed or twisted in. If you do not wear glasses, pull the rings or eyecups out. If you do not have the eye relief adjusted, your view will be like having a ringside seat but you are looking through a knot hole.

  2. Interpupilary distance is the distance between your eyes. Adjust by bringing the two parallel telescopes closer or farther apart until you see ONE circle, not two, as seen in movies to show that someone is using binoculars.

  3. Diopter setting ring is usually located on one of the eyepieces.


  1. Focusing knob. When you see a target, bring your binoculars up to your eyes and adjust the center focusing knob to bring your target into sharp focus.

In the field, you will usually use your naked eyes to spot the birds. Then you should keep looking at the bird while bringing your binoculars up to your eyes. This saves time searching for the bird once your binoculars are raised.