Step by step
The first step is to determine whether your binoculars are really out of collimation. Observe a bright star and defocus the right-hand eyepiece. Any displacement of the focused star from the centre of the defocused one is the error you need to correct.
It’s a good idea to locate the collimation screws in good lighting. They will be small and may be covered by casing and adhesive. Remove material that’s covering them. Then choose the correct size of flat-head screwdriver to turn the screw and break any locking adhesive.
Even if you don’t normally mount your binoculars, you should do so now. Polaris, if you can see it, is a good target for collimation as it doesn’t move appreciably. If you choose a terrestrial object, pick one that’s at least a kilometre distant.
The collimation screw tilts the prism against the tension of the spring clip. Look through both eyepieces, and rotate each screw by no more than one eighth of a turn at a time to see what effect it has on the image, then return the screw to its original position.
Make sure that you have set your binoculars to your interpupillary distance ( IPD) then, using what you’ve learned about the action of each collimation screw, merge the images into one, again using no more than one eighth of a turn of the screw each time.
When you think you have the images merged, check the IPD again and use the Bahtinov masks or anaglyph glasses to make sure that they’re as closely merged as you can get them. Lastly, use them normally and enjoy the new and improved view!
NOT COLLIMATED COLLIMATED