This How To is about recollimating (or fixing double-vision) on binoculars. Before proceeding, you should check to see if your binocs are under warranty, because following this 'ible will most likely void any of those.
Also, the instruction set herein is true for all of the binocs I've repaired, which is quite a few since I foolishly let onto my friends that I did my own. But maybe your pair is different.
Ah, binoculars! What a wonderful boon to backyard astronomers, nature lovers, and even sports fans. But what a waste of space if they are off kilter. But before dissecting that old pair, or chucking them, try this method for fixing double vision.
Collimating is a word astronomers use when talking about fixing up their scopes. A well collimated scope allows a column of light to pass through the objective lens, bounce off any mirrors, and enter the viewing lens straight into your eye. A poorly collimated scope dims an image, and/or makes it hazy. It is often the result of the objective lens or a mirror not sitting 100% correctly with the scope's barrel. The light will not travel from the objective lens to whatever mirrors and then to the viewer correctly.
In the binocular world, you have to consider not one, but two columns coming together to make an image. Fortunately for binoculars, the problem is much less likely to result from the objective lens sitting askew. Rather, the usual suspect for poorly collimated binocs (double-vision) is that one of the prisms has fallen out of adjustment.
A lot of folks armed only with this knowledge will simply adjust the screws on one side until the double vision is "fixed." However, true collimation is the result of getting the light to enter the center most part of the objective lens and following a path to the center most part of the viewing lens. If you simply adjust one barrel until the double vision is gone, you'll get rid of that problem, but you won't have nearly as much light coming in, resulting in dimmer, less sharp images. Following my method accounts for that and allows us to collimate much more proficiently.
Sometimes your binoculars fall out of collimation because you dropped your old pair of field binocs. Sometimes this happens because the package delivery service guy dropped your new pair (in which case, again, check for a warranty before going any further). Maybe they weren't collimated correctly before leaving the warehouse. For whatever reason, you have a pair with double-vision, and that just won't do. Let's fix that.
Step 1: Gather Some Supplies
1. A pair of jenky binocs. Porro prisms are much easier to adjust than roof prism binoculars. Those aren't brands but the way these two designs work shows in the shape of the pair. Look at the pic to figure out which your kind are. Porros are usually bigger and have that classic "binoculars" look, like someone in WWII would have used, whereas roof prisms are sleek and often marketed as "portable" or some such word meaning small.
2. Technical (small) screwdriver set. Most brands use tiny slotted screws, though some like to get creative.
That's all you NEED need. But here are some things that will come in handy:
3. A lake with two sides you can access.
4. A sign with an "+" on it. You can make one with a marker and a piece of cardboard. Use the black marker to make four squares on the sides, rather than a black + in the middle. You'll see why later. As long as you won't be cited for littering, hang the sign from a tree with a plumb weight tied to the bottom center. I used the cross on a church once. I typically use a rig across the lake I live near. It has beams that work perfectly. Whatever you use, you want the "+" to be (a) level with the ground and (b) near a vertical (plumb) line.
5. A tripod and a tripod adapter for your binocs. "But, Alan," you say, "I don't have a tripod adapter, don't want to buy one, and I'm not even sure my binocs are tripod mountable." I got you covered. Check out this Instructable by yours truly!
6. A pen knife if you are willing to permanently alter your binocs or some glue if you are not.
7. A laser pointer. Yep. That's what I said. And grab a ruler and some tape while you are at it.
8. A lot of patience.
Step 2: Locate and Expose the Adjustment Screws
Often the companies producing the binoculars hide the adjustment screws under a layer of rubber or latex or etc. This serves two main purposes.
First, the layers do actually protect those screws and the inside of the binocs from the elements. The last thing you want is water in your binocs. Ugh! However, this isn't likely to happen just by exposing those screws.
Second, they keep people from messing with them. You can mess with them by accident, or on purpose. And it's great that the layer of whatever material they use on yours protects you from accidentally touching the screws, but you should be able to do it on purpose when you need to.
So, referencing the pic above, either peel back the coating from the adjustment screw nearest the viewer (to glue back later) or, using a hobby knife, cut off the layer just where the screw is. If you cut out just that area then the layer that surrounds the screw will keep you from accidentally touching the adjustment screws.
You can do the same thing for all four screws, but I highly recommend leaving the front screws (the ones near the objective lens) alone until you are absolutely sure those prisms are the problem. The fact is, the screws nearer the viewer are much, much, more likely to fall out of adjustment.
Now don't get out the screwdriver just yet...
Step 3: Determine Which Lens Needs Adjustment
Determine not only which lens needs adjustment, but which adjustment(s) you need to make.
1. Hang your + target or identify one.
2. Get about 500 to 1000ft (or a little longer than a football field) away from the target, but on level with your target. This is assuming your binoculars are 10x or greater magnification. Get closer if not. A lake comes in handy here because unless you have surveying equipment, a lake provides a pretty good clue that you are about level with your target. If your target is on a tree near the waterline, and you sight from near the waterline, you are much closer. And this process should be pretty close, though it doesn't have to be exact.
3. Look at your target though the binocs and try your best to focus them.
4. Attach your binoculars to your tripod making sure the binocs are level and plumb. Lock down the tilt once level. This is easiest if your tripod comes with the bubble levelers, but if not, use a string tied to a heavy thing to make sure the neck of the tripod is straight up and down, and use a leveling device (can be as easy as a marble in a plastic tube, slightly larger in diameter than the marble) to make sure the binocs are level.
5. I like to make sure the center of the binocs is lined up with the tripod head and tape a laser pointer, also leveled, to the side of the tripod head. Then I can aim the laser pointer at the target. One the beam is on the target, I lock down the pan.
6. Look through your binocs one eye at a time. They should be close to, if not on the target. If you've lined up everything correctly. One of them, however, is likely right on the "+" and the other is a little off. If they are both off, things could get really fiddly. Choose the one that is closest to the cross of the two lines and put it dead center.
7. Assess the image that is off-center. Is it right of the center? Left? Above? Below? Make sure your binoculars are level again before deciding that they are off above or below the mark.
8. Make sure once again that everything is locked down and that one of the sides is square in the middle of the target.
9. Looking at the side that is off, if that side falls to the left or right of the center, then you need to adjust the horizontal. If it falls above or below the center, you need to adjust the vertical. If it is both right or left AND above or below the mark, then yes, you'll have to adjust both, but never adjust both at the same time.
Step 4: Adjusting
To adjust, general: IMPORTANT!
1. The screws you uncovered are adjustment screws, meaning they are meant to be in a particular spot, not all the way screwed in. They butt up against the prisms inside, and if you adjust too much one way or another, you can bust the prism off the wall, in which case, you've broken your binocs. So go slowly and make the most minor adjustments per time.
2. Also, keep track of your adjustments. I adjust about 1/8th turn per adjustment until I get super close and then I adjust even less. Have you made one clockwise turn? Half of one? If you know, and you figure out you went the wrong way, then you can get back home more easily.
3. When you adjust, look at the target through both eyes. After every adjustment, yes, every single one, take a break. Don't adjust a quarter clockwise, decide that was too far, then come back an eighth and THEN take a break. Take a break after you adjust a quarter clockwise. It only takes maybe five seconds to break. Then you can go back to it and come back that one-eighth counter-clockwise if it still looks like you should.
The reason for this is that your eyes will naturally try to adjust to the image at the same time that you are adjusting the image through the binocs, so you cannot trust your eyes that you went to far in the first place.
To adjust horizontal: The horizontal adjustment can be made by making very small adjustments to the screw nearest the viewer. If your horizontal does not need adjustment, then you can adjust only the vertical. However, if they both need adjustment, start with the horizontal, make sure you have it just where you need it, and then transition.
To adjust vertical: Again, if you need to adjust both horizontal and vertical, fully adjust the horizontal first. The vertical adjustment is more fiddly and fragile. In order to adjust the vertical, adjust the screw closest to the objective lens.
When finished, if you pried up the rubber to get to the screws, use some quality rubber glue if your rubber won't snap back over them. If you cut open the rubber grip just over the screws you should be fine. I've heard that some people feel weird about leaving the screws uncovered and they will coat them with hot glue. I haven't tried this, and haven't had a problem leaving them exposed myself, so I'll just mention it, rather than recommending it.
Step 5: Testing
Once you think you've got it, test it out.
There are two tests to try. First, look through the binoculars and slowly move them back away from your face. You should notice a beam of light coming out the viewing lens (eyepiece lens). These lights should seem to come straight back. If one of them is crooked, then you have the images lined up, but the light is not entering the center part of the objective lens of the one with the crooked beam. This means, you aren't getting all the light you could out of them and the images are less sharp and more faded than they could be.
Once you have the beams straightened out, next, try out your newly fixed binocs on some stars (the night ones. NEVER point binoculars at the sun! Especially when you are looking through them, but even ever). Can you see just one bright, night-sky object? Try the moon if it's out. Does it appear crisp and just so beautiful? Great! You are finished! Now you can see images as crisp and clear as the photo above (that's my dog, Lido by the way. She says, "hey!")
If you followed these instructions and you didn't quite get there the first time, you get to go to the lake again. Win/win.