YOU HAVE GOT A COLLIMATION PROBLEM!
By far and away the most common fault that binoculars suffer from are collimation problems. A binoculars collimation can be the result of any of the above problems and in some cases all three. So what is collimation and how does it affect binoculars. Wikipedia offers the following definition: ‘Binoculars, field glasses or binocular telescopes are a pair of identical or mirror-symmetrical telescopes mounted side-by-side and aligned to point accurately in the same direction, allowing the viewer to use both eyes when viewing distant objects. The crucial part is that both halves of a binocular point accurately in the same direction, if for any reason they no longer point in precisely in the same direction the binocular is said to be out of collimation.’ Depending on how badly aligned the binoculars are, they can be mildly uncomfortable to totally unusable. If you feel that your binoculars feel like they are trying to pull your eyes out your head they are almost certainly out of collimation. The effect is the same as if you cross your eyes on purpose, and just as uncomfortable! The human brain, the most wonderful organ yet discovered in the universe, is very good compensating for minor misalignment of our eyes, it deals with the problem every day, and we have to have a pretty hefty smack to the head before the brain can’t compensate anymore and we see double. Collimation issues become more apparent as soon as we use binoculars because the greater magnification exacerbates the problem.
Unless a binocular has become so badly damaged that it is apparent that the two halves are pointing in different directions it is almost impossible to tell from the outside that a binocular is out of collimation. This is because the problem will almost invariably be with the alignment of the internal prisms. There are a number of reasons that binoculars lose their collimation. The most common cause is a drop or knock that physically moves the internal prisms. Another major cause which is less obvious is to leave a binocular in direct sunlight for a prolonged period. This can have a number of disastrous consequences for a binocular. The temperature internally can climb rapidly, the different materials that the binocular is made of will expand, probably at different rates, causing the materials to flex as the temperature rises, and go out of alignment. You may be lucky in so far that all the components contract to where they were before they got hot, but there is a very good chance they won’t and the next time you go to use them they will have lost their collimation.
In all but the cheapest binoculars it is possible to get them re-collimated but it is a job for the experts. If you think that your binoculars may be suffering from a collimation issue please ring the number at the top of the page and talk to one of our staff who will be pleased to talk you through the solution to the problem.