How to Fix Double-Vision on Binoculars




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

You'll need:

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.

Here's how:

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.



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    19 Discussions


    6 months ago

    Glad I didn't throw them away! Thanks to you and a couple of other instructions on the net and youtube I got to understand. I'll get to keep the new pair I bought. But this pair works fine. I gave somebody a pair years ago. I'm gonna go there and fixed them for him.

    Thank you and thank google and youtube and the internet. Nothing is impossible. DIY is the way to go. Not here in the U.S. everything is throw away. But in most parts of the world it's how it is. thanks


    9 months ago

    It's good to hear from you -- I had no idea if you still keep an eye on this site, but then I guess it sent you an alert. Yes, your Instructable was most inspirational.

    Since alining the Celestrons, I found 2 other pairs of my porro prism binocs were also out of alinement, so I adjusted them too, but I didn't use the laser: for one thing it would be tough to mount the laser on either one of them, as their hinges are short and lumpy; also I didn't expect any serious defect in one particular scope in either pair, just general distributed misalinement, so I simply distributed my adjustments between scopes in each pair, and they are fine now.

    Now another question: have you ever worked on 'roof prism' binoculars? as I have a pair of them that are a bit out, and it seems that someone else is also wondering. I suspect that 'roof prism' is some kind of misappropriated term (I know, not yours) and that in fact they have no prisms, just straight-through scopes -- I can't see what purpose prisms would have in them, so alinement might require a bit of dis-collimation in one or both scopes to approximate alinement. Otherwise some shifting of the hinge at one end, if possible.

    Thanks, O.


    1 year ago

    Hello Alan, thanks again for your down-to-earth instructions; for a great start I didn't even know binoculars had adjustments, now I'm working on a big pair of Celestron Skymasters and found them right away -- terrific. However someone else asked what you mean by horiz. vs. vertical adjustments and I don't think your answer cleared it up for them, though in this case it seems obvious to me, but maybe not to them. I know in other situations, inverse terms like that can be easily confused. Now WHY I mention it is that in these Celestrons, the screws closest to the eyepieces adjust dead vertical, not horizontal as you said, while those closest to the objectives adjust strongly diagonal, not vertical. I would say that by horizontal you must mean the screw makes the image for that tube move from side to side (ie., horizontally), not up and down. On that basis I'm saying that the 'eyepiece' adjustments on these binoculars move their images vertically, but that may be just these Celestrons.

    My problem is that I NEED to move the images horizontally to merge, in fact the images are reversed, viz., the right-tube image is left of the left-tube image. As it is, the only screws that adjust them horizontally at all are the 'far' ('objective'/diagonal) ones, so it seems I'd have to move both images diagonally to get them closer together in the horizontal sense, then use the near ('eyepiece') screws to move them closer together with vertical movement.

    Now it turns out that with the far/diagonal screws already loose -- so they can not bring the images any closer together -- the images are still reversed and too far apart -- barely 'mergeable' by my eyes -- causing eyestrain quite quickly. It seems I'll need to open up one or both tubes to correct something that has been knocked out of place -- likely by being dropped, as one objective finish ring is chipped and broken, for example. Most likely ONE tube is at fault, so I'd like to find out which one it is before taking the wrong one apart.

    My method would be to aline the 'frame' of the binoculars on a target, and then see if it's badly off-centre in one tube (or both). In the case of binoculars, the hinge between tubes qualifies as a frame or reference. You mentioned using a laser, which should be fine, but I don't think it would work as you briefly described; for one thing it would have to be alined very accurately with the hinge, otherwise there'd be little point in messing with it -- you may as well just bring the images together as well as possible with the adjustments, and never mind where each one SHOULD be (as you mentioned yourself). For another thing, laser pointers are not lab equipment, so the beam can come out of them in any direction and still be 100% functional for pointing; but in this case, the beam needs to be very accurately alined with the hinge of the binoculars, and the easiest way to do that is for the beam to be alined with its own tube, and then aline the tube with the hinge. Luckily these Celestrons have a superb chrome hinge rod, and I've been experimenting with making an H-mount to adapt a pointer (in the top of the H) to the hinge (in the bottom of the H), and also modifying a typical inaccurate laser pointer to come 'straight out' of an outer tube by shimming, rewiring, etc.

    I'm still fine-tuning my laser aim, but so far I get the impression that the bad tube is the 'other' one, not the one with the broken objective ring.

    Again, I thank you for kickstarting me on this repair (a couple of years after you posted your instructions), but if you notice anything familiar or something I missed, or have any comments, I'd love to hear them.

    Cheers for now, O.

    1 reply

    Reply 9 months ago

    Wow! Just saw this comment! I'll have to trust you on your method. I was rather sloppy with the laser, it seems, trusting it to be close enough at about 100 yards or so. But you're absolutely right, calibrating to the hinge (even assuming the hinge is true, which is not always the case) is rather "pointless" if the laser itself is not calibrated true. Hmmm...I suppose I've been lucky. One thing you could do, absent surveying equipment, is to find a fixed, horizontal surface, such as a picnic table, screw two small eye-bolts into scraps so that you can move and level them easily, place one on each end of the table, level the openings, and point the laser through both, moving the and leveling the scrap wood as needed. Then you would have a level line, but one would have to figure out exactly how to then level the binocs along this line.

    I'm glad, if nothing else, I could provide inspiration. Best,


    2 years ago

    Been there. Same brand and everything. Sigh. They don't make them like they used to.


    2 years ago

    Alan, thanks for the great instructions!

    I still have a couple of questions, though:

    1. when you're saying 'vertical adjustment', do you mean that a horizontal line going through the image should not look 'broken'? so that to adjust the image the edges of the 'breaking point' need to be moved vertically to match?

    2. the instructions are for a fixed magnification binos. is it realistic at all to adjust a zoom binos without special equipment?

    2 replies

    Reply 2 years ago

    Thanks for the questions.
    1. The image should not look crossed (as in the original pic). They can look crossed (vertical) stacked or offset (horizontal) or often a combination of the two.

    2. Honestly I haven't played around with zoom nocs much. I've used a few and felt like not enough light would come in based on the objective. So I cannot answer that question. However, if you have a pair of zooms that would cost more to fix than buy again, and you decide to play around with them, I'd love to see what you find!


    Reply 2 years ago

    Thanks for the response.

    I honestly decided to return them and got Celestron UpClose G2 20x50 (kind of a budget option).
    They are still misaligned and I definitely need to adjust them (I feel I will never get a good factory-collimated nocs from Amazon anyway and going through rounds of replacements isn't worth it)


    2 years ago

    Where are the adjustment screws likely to be on a roof prism binocular please?

    Left-field Designs

    2 years ago

    good instructions, I learned the hard way years ago to have someone else check. I ruined a good set of binos trying to fix this problem. turns out I don't have binocular vision due to a large disparity in the focal range of both my eyes, unbeknown to me I have extreme long sightedness in one eye and extreme short sightedness in the other coupled with stigmatism. I get double vision but on the diagonal and my solution is to turn the binos on their side and use them as a monocular.

    1 reply

    I'm sorry to hear about your different focal ranges. I think the world of monoculars, sights, and telescopes, just FYI.


    2 years ago

    Columnizing? Perhaps collimating is the word to use for telescopes. Good info here, thank you.

    3 replies

    Right you are, stringstretcher. Collimating seems to be a much more common word in gerneral. My peeps use "collumnizing," which is a word, and does seem to apply, but digging a little I see that collimating is much more favored. For this reason, I'm editing my 'ible to use collimating so I can get more folks in on the convo. Thank you.


    Sure, thanks. I met a man a long time ago who did this for a living with high end binocs. We're talking thousands of dollars a pair binocs. He had TWO 8 inch telescopes and TWO 30x rifle sights on a bench to adjust and collimate them. He had worked for Kodak for years as an optical engineer. I learned so much from him. I have a pair (NOT in that price range) I need to work on, thanks for the instructions.


    Best of luck! Let me know how it turns out. Sounds like a great pair. Check the objective lens first though to see that it hasn't been knocked out of place. Some of the older pairs had that problem.


    2 years ago

    Thanks!!! I'm eager to try this. I've a set my sister gave me when I was 8. Metal bodied, real glass lenses and HEAVY. My youngest dropped them and they are double imaged. I was heart broken but couldn't throw them away for sentimental reasons. Maybe this will fix them!

    1 reply

    Reply 2 years ago

    Great! Let us know how it turns out. Check the objective lens though because on some of the older pairs, they came dislodged more easily.


    2 years ago

    I swear, I must have always been using binocs that were out of adjustment. I thought this double vision was just how they worked! Not kidding.

    My wife's got a pair, going to see if I can adjust them. Thanks!

    1 reply