How To Tell If Your Binocular Is Out Of Collimation

A binocular is actually a pair of refractor telescopes joined together. The alignment between these two telescopes is called “collimation”. Proper collimation is critical to a binocular’s performance, and the user’s viewing enjoyment. The brain can do a remarkable job of compensating for poor collimation, but has more trouble doing so on the night sky due to the much lower amount of visual information. For this reason, good collimation is especially critical for astronomical binoculars. Every Oberwerk binocular is thoroughly examined, tested, and collimated before shipping to our customers. But because collimation is occasionally lost due to rough handling during shipping, or from accidents (dropping the binocular), we are providing instructions for collimation here.

Surprisingly, collimation adjustment is easiest to perform in daylight. Collimation can be quickly be checked by viewing an obect with distinct horizontal and vertical lines, such as a house, building, or fence, at least 100 yards away. It is best to do this outdoors, as viewing through a window can cause distortion from diffraction. Begin by focusing on the object. Alternate viewing with the left and right eyes by gently closing one eye at a time. Alternate eyes about once per second. Relax your eyes as you do this so they are not compensating for misalignment. Notice that the object will move somewhat as you alternate eyes, the same as if you were doing the blink test without looking through a binocular. A slight amount of horizontal movement (to the left with the left eye, and to the right with the right eye), is normal (same as doing the blink test on the target without the binocular). Excessive horizontal movement, or any amount of vertical movement, should be corrected.

To check vertical collimation, look at a distinct horizontal line, such as a roof line, gutter, or fence rail. Slowly move your eyes back from the binocular until they are about 3 inches away, while maintaining the view of the horizontal line in eyepieces. Let your eyes relax and focus more on the image at the eyepieces rather than through the binocular. Even a slight vertical miscollimation will now be readily shown as a difference in position of the horizonal line.

Now that we can determine collimation problems, how do we correct it? Check out the posts below under “related advice and info” to find collimation instructions for your Oberwerk Binocular!