There are a few binoculars on the market that have externally accessible screws that allow you to adjust collimation, but these comprise a very small percentage of binoculars on the market. Most of these are larger astronomy binoculars.
Otherwise, for the vast majority of binoculars, you must return the binoculars to the manufacturer if they need collimation and, be advised, if you open the binoculars in an attempt to play binocular repairman to get at the prisms to do collimation,yourself, you void the warranty and, if the bino is waterproof, you ruin the waterproofing. It also takes special tools to get inside a binocular, not to mention some know how. In my experience, most cases of folks who opened their binoculars, for one reason or another, end, badly. Believe me, the folks that repair binoculars for a living are not thrilled to get a box of binocular parts and then get asked to fix the binocular as good as new. This is not a do-it-yourself-project.
Perhaps my question was not clear. I was not asking how to collimate a pair of binoculars. What I want to know is how to tell if they are out of collimation. If they are, then I want to send them back. On the other hand, I do not want to send them back if there is nothing wrong with them.
With my old binoculars, I had no problem; I could get a nice single field of view at all distances. Not so with my new ones. The field is nice and clear at infinity, but as I focus closer, at some point I get two overlapping fields. I can minimize it by playing around with the eyecups and the interpupilary distance, but it is very annoying.
However, I am not sure that it is necessarily the binoculars as I have the same problem with many other pairs. Thus I am wondering if it is me or perhaps even my new eyeglasses as opposed to the binoculars. So, how do I tell if it is really the binoculars?
Any and all help appreciated.
Anytime you cannot merge the two fields of view into one, no matter what the focus point, the prisms are out of alignment. This is a case of being severely out of collimation. In less severe cases, you will feel tugging or eye fatigue (see below). Focusing at different distances won't make it go away if it is a prism issue.
Anytime the shape of the field changes at any distance other than at minimum focusing distance as you focus, as with your binocular, you probably have something bent or out of alignment in the focusing mechanism, perhaps a bent eyepiece barrel or something is sticking if you have an external focus binocular. This can cause one eyepiece to be at a different level as the binocular focuses. Zoom binoculars are especially prone to this type of problem, since they add a fragile zoom mechanism into the focusing system and keeping everything in alignment is iffy. Do you have a zoom? From what you describe, I suspect your binocular falls under this category. Bottom line is the same, either way - you have a faulty binocular and should return it.
Be warned, though, that new eyeglasses can give you fits until your eyes become accustomed to them. It has happened to me. If you still have your old glasses, put them on. if your new bino is still not right, I'd guess your new bino is out of collimation. Should not be any different than your old binocular.
A common problem is a binocular that is only somewhat out of collimation. No double images, but you will get eye fatigue and will sometimes you will feel a tug on one eye or the other. Viewing just seems uncomfortable. May not seem like a big deal, at first glance, but it will cost you dearly in eye fatigue, headaches and blurred vision if you use the binocular for any length of time.
How can you test this? First, make sure the diopter has been set correctly for your eyes. Then, focus, carefully, at an object at a distance of say forty yards or more. Then, cover one barrel with your hand so that you are only seeing out of one barrel, but keep both eyes open. Do not close one eye. Wait a couple of seconds, then take your hand off the barrel it was covering. If your binocular is properly focused, the image should pop back in focus almost instantly with both barrels. If the bino is out of collimation, the image will not come back into focus, instantly, but will seem to hesitate and struggle to come to focus.
If you have looked through binoculars of all kinds for testing purposes, as I have, you can get quite good at detecting even slight cases of a binocular being out of alignment simply with one look. Also, when you have used a binocular.
Hope this helps
I finally was able to get out during daylight when the weather was other than miserable!
I performed the test you described and there were no issues whatsoever. Unlike my previous binoculars, the new pair has twist-up eyecups. As I wear eyeglasses, I expected that I would need to leave the eyecups fully down to be as close to the lens as possible as was the case with my previous binoculars. It turns out that I need to partially extend the eyecups for the binoculars to work properly. Quite a surprise for me as I always thought that eyecups would need to be fully down for those of us who wear eyeglasses.
Thank you very much for explaining how to test for collimation.
Glad you got that resolved. That's great.
Yes, there can be such a thing as too much eye relief, even if you wear glasses! I have experienced the very same thing on several binoculars.. To keep the eyecups at the correct height for my glasses, I went to a hardware store and bought some O rings of the right size and slipped them under the eyecups to raise them up, slightly, from the full down position. Might be worth a try if the eyecups on your binos don't stay put.