If binoculars are misaligned, they will display double images and be blurry. How we adjust:

If binoculars are out of alignment, they will display double images and be blurry. Adjustment is usually simple and can be performed most accurately using an artificial star.

Here you can see the "inner workings" of a binocular. The prisms must be moved (adjusted) until they are aligned. This is done with Allen screws at the location shown. To do this, the rubber protection must be lifted.

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