How do I know if my binoculars are out of line?
When binoculars are out of line it causes eye strain because your eye muscles work to pull the two images together. One test is to focus your binoculars (properly) on a nearby sign with detailed lettering. After making sure both eyes are correctly focused, take your binoculars and rest your eyes by looking off into the distance. After about 30 seconds look at the sign through your binoculars again on the place where you were previously focused, paying careful attention to the detailed lettering. If your binoculars are out of line, within the first second of viewing the letters will initially appear blurry, but then become clear. That’s not good! If your binoculars are in line, the letters should look crisp and sharp as soon as get your binoculars on them.
Here’s another way to check alignment (collimation)