The planet Jupiter seen with collimated binoculars.
When the series of lenses and prisms in each of a binoculars' barrels align perfectly, they produce a merged image and are said to be "collimated." Rough handling during shipping or use can knock binoculars out of collimation. Miscollimated binoculars produce fuzzy or overlapping images and possibly oval, cat's eye-shaped exit pupils, the miniature images you see in each eyepiece. This can lead to eyestrain, headaches and a degraded user experience. To correct miscollimation, manufacturers build adjustable prism tilt setscrews into many of their models. If prism tilt is excessive, however, or lenses are misaligned lenses, have a professional collimate your binoculars.
Instructions
Checking Horizontal Collimation
1. Go outdoors in daylight and focus your binoculars on any large object with distinct horizontal and vertical edges, at a distance of about 100 yards.
2. Relax your eyes. Alternately open and close them, about every second. You should see the binoculars' image move slightly to the left when opening the left eye and to the right when opening the right eye. This slight movement is normal and desirable.
3. Adjust the prism tilt screws to restore collimation if you detect more than a slight amount of horizontal movement.
Checking Vertical Collimation
4. In the daytime and outdoors, look at a distinct horizontal line, such as a roof line, gutter or fence rail.
5. Slowly move the binoculars about 4 inches away from your eyes as you keep looking at the images in the eyepieces.
6. Check that the horizontal feature you focused on remains an unbroken straight line--in other words, no part of it is displaced vertically.
7. Adjust the prism tilt screws if you detect any vertical displacement.
Adjusting the Prism Tilt Screws
8. Locate the two prism tilt setscrews just ahead of the eyepiece on each barrel. For rubber-armored models, pry up the rubber covering with your screwdriver to expose them. Be careful not to overstretch the rubber; you want it to snap back to its original position when done.
9. Remove the protective glue from the setscrew's top and insert the screwdriver in the slot.
10. Turn the right barrel's setscrew clockwise in very small increments to move the image in the right eyepiece to the left and down, counterclockwise for up and right.
11. Turn the left barrel's setscrew in the same manner, clockwise or counterclockwise, to adjust the image's horizontal and vertical alignment in the left eyepiece.
12. Adjust one or both setscrews as necessary, frequently checking progress using the horizontal and vertical collimation tests, until the two images merge horizontally and there is no vertical displacement.
Tags: prism tilt, horizontal vertical, Adjust prism, Adjust prism tilt, barrel setscrew