How to align prisms in binoculars

Written by brandon maxwell
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How to align prisms in binoculars
Binoculars with a centre focusing ring (Frank Lukasseck/Polka Dot/Getty Images)

Binoculars are a great tool for many outdoor recreational activities. Whether helping us see small objects from great distances, or helping those with bad vision see normal spectator sports better, binoculars can help bring added enjoyment to a multitude of sports. By definition, binoculars have two eyepieces that you look through in order to see the magnified object. When these two eyepieces are not aligned, the binoculars will not function correctly and eyestrain and headaches can occur. By properly aligning the eyepieces, you can ensure proper functioning and healthy eyes.

Skill level:
Moderately Easy


  1. 1

    Determine which of your eyes is your dominant eye. Focus on a distance object and then cross your hands at arms' length, leaving a 1-inch gap between your hands. Center the object in this gap.

  2. 2

    Close one eye. If the object is still centred in this gap, the eye you have open is your dominant eye. If the object disappears and a different image is in the gap, then the eye you have closed is your dominant eye.

  3. 3

    Look through the binoculars with your dominant eye only. Adjust the focus ring until the image is clear and sharp. Now open both eyes. If the image is still sharp, then the prisms are adjusted correctly. If not, you will need to adjust them.

  4. 4

    Look through the binoculars again, still focusing on the same object. While continuing to look through the binoculars, adjust the collimation alignment ring. "Collimation" refers to the optical alignment of all the elements of the binoculars. The alignment ring is usually at the base of the centre focus ring.

  5. 5

    Twist the collimation ring in both directions until you find a setting where the object appears sharp. The collimation is now set and all optical elements are aligned.

Tips and warnings

  • Once you have the collimation, or alignment, set, you can mark on the collimation ring with a white pen the location that provided the appropriate setting. This way, you can quickly tell at a glance whether the binoculars are out of alignment.
  • Neglecting to align the optical elements can cause severe eyestrain, so it is best to check the alignment and properly maintain your binoculars on a frequent basis.

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