When you look through your birding or deer hunting binoculars, you expect to see one clear image of your target. So if instead, you see two blurry images of the target, you know you have a problem. But do not fret as it is possible to fix the double vision problem in binoculars.
Fixing this problem entails a process known as re-collimation, which sounds like a big and complicated word but is really not. And in this article, we will be discussing how to fix binoculars with double vision.
What Is Collimating?
But first, what is collimating? Collimating is defined as making rays of light parallel. This often involves the accurate alignment of an optical system such as a binocular. In binoculars, it is the process of aligning the optics to parallel one another.
Binoculars are made up of two tubes that act as independent optical systems. Double vision occurs when these two tubes are not parallel. This can happen due to a knock or a drop which causes prisms in one tube to be out of alignment.
When Does My Binocular Need Fixing For Double Vision
Sometimes the misalignment of the optics may be unnoticeable. However, not always, and there are times when you will need to re-collimate the binoculars.
There Are Several Things To Look For Before Fixing Double Vision Problem In Bincoulars
- It is normal to notice a slight double-vision appearance at close focus distances. If this is what you are experiencing, there may be no need to fix the binoculars. However, at long ranges, double vision will signify misaligned optics and cause fatigue. Thus if you notice double vision when glassing from long range, you will need to collimate the binocular.
- It is difficult to have double vision at low magnification as your brain can compensate. However, at higher magnifications, double vision will be noticeable. Therefore at higher magnifications, proper alignment is a necessity.
- Binoculars come collimated from the manufacturer. But it is normal for the optics to get misaligned during shipping due to rough handling. It is also possible for the prisms to get misaligned due to accidental knocks and drops when in use. This is something to expect during shipping or when you are using the binocular out in the field.
- If the binocular is under warranty, it may be good to send it back if it is misaligned instead of trying to fix the problem yourself, as this will void the warranty.
True Collimation Vs. Conditional Alignment
When the collimation is being discussed, you will often hear the terms true collimation and conditional alignment mentioned. So what do these two terms mean, and which one should you pay close attention to?
Let’s start with true collimation. This refers to aligning the binocular at its 3-axis points. Okay, so what does that mean exactly? Well, the three-axis points are the hinge and the two optical prisms inside each tube of the binocular.
In essence, the left tube should be parallel to the hinge, while the right side should be parallel to the left tube. This results in zero double vision across the entire IPD range. In addition, true collimation involves adjusting the objective lens, so they are parallel to the optical axis. (ref: 1)
It is important to note that adjusting the objective lens requires special tools and is best handled by an expert.
On the flip side, conditional alignment is simply adjusting the optical tubes at one IPD setting. This results in somewhat better performance and minimal double vision. However, it does not address poor collimation.
Also, conditional alignment only aligns the tubes at a specific IPD setting, and the effects of the alignment will not be noticeable at a different setting.
So what does the acronym IPD stand for? IPD stands for interpupillary distance and is measured in millimeters from the center of one pupil, and typically ranges from 52 to 76mm. In some binoculars, you will find a hinge for setting your preferred IPD.
Results Of Not Calibrating For Ipd
You may be wondering why do I see double through binoculars? Well, it may be because you did not calibrate the IPD. When the IPD is well-calibrated, you will be able to have a clear field of view in both eyepieces without any clipped images. When you do not calibrate for IPD, you may also notice clipped images and distorted exit pupils. Also, when you move the binoculars from left to right, you will notice that one side darkens faster than the other.
Problems Associated With Poor Collimation In Binoculars
Firstly, poor collimation causes double vision in binoculars. Due to the double vision effect, a poorly collimated bino will also cause eye fatigue, headache making it harder to continue using the binocular.
Checking For Poor Collimation
To check if your binocular is poorly collimated, draw a big “t” target and place it at least 100 yards out. You can also use a house/building rooftop or fence.
Checking for Horizontal Misalignment.
Once you have your target set up, look at it through the binoculars and focus on its horizontal lines. Close each eye after a second. If you cannot detect any misalignment, pull your eyes from the eyepiece by an inch or so.
Focus on the top of the field of view and look for the clear misalignment of the horizontal lines
Checking For Vertical Misalignment
While focusing on the target, check to see if you notice any vertical misalignment by focusing on the vertical field of view of the target.
Why Just Adjusting The Screw Is Not Enough For Fixing The Double Vision
If you wonder how to repair binoculars ‘ double vision, then adjusting the screw is not the way to do it. As mentioned, true collimation, which is what you want, is adjusting all three axes. Adjusting the screws alone will not cure the binocular of its poor collimation.
What Causes Misalignment Of Optics
So what causes double vision in binoculars? The most common causes of double vision in binoculars are rough handling during shipping and accidental knocks and drops when in use.
How to Fix Binoculars with Double Vision?
Now that you better understand why your binoculars have double vision, it’s time to fix the problem. Before we delve into how to fix double vision in Bushnell binoculars, there are some tools you need. The tools you need are a set of small screwdrivers similar to those used on eyeglasses and a tripod adapter. Once you have the tools, you can proceed with the adjustment.
Total Time: 1 hour
Step One: Locate The Adjustment Screws
The first thing you need to do is locate the adjustment screws. You will need the instructions manual for your binoculars for this. But what if you don’t have the manual? Well, don’t fret, as the location of these screws is pretty much the same in all binoculars. The horizontal adjustment screws are typically located near the eyepieces. You will notice an adhesive strip that you can remove. A razor blade can help speed up the process. Be cautious not to scratch the lenses, though. The vertical adjustment screws are found on either side of the binoculars. They are noticeable by the plastic screw-holding casings that cover them. In some models, you may also notice a strip of adhesive that sits slightly on the binocular.
Step Two: Test The Binocular
The next step is to test the binocular’s alignment. The best time to do this test is on a clear night. Attach the binocular to a tripod and focus on the brightest star in the sky. Ensure the binoculars stay mounted in the position you place them. If the collimation is out of alignment, you will notice 2 stars. Focus on one stat and not a cluster or the moon, as you may not see the fine lines when focusing on large targets.
Step Three: Defocus One Lens
This may sound strange, but it makes aligning the lenses easier. Pick one eyepiece to defocus and turn it so that the start appears large and unfocused when looking through that eyepiece. And on the other eyepiece, the image should be clear.
Step Four: Align The Horizontal Screws
Start with the horizontal screws and make adjustments of ⅛ inch of a turn at a time. Adjust each side equally. Adjusting the horizontal screws will not bring the two pictures into perfect alignment, though, and you will need to adjust the vertical screws as well. Take a five or ten-minute break after each turn.
Step Five: Align The Vertical Screws
With the vertical screws, do the same thing you did for the horizontal ones. This means adjusting the screws each at a time and taking breaks in between each adjustment.
Step Six: Refocus The Lens
Once you have aligned the two images, refocus the unfocused lens. Everything should be good now, and you should see a single clear image.
Fixing the double vision problem is a task you can perform at home. The above steps we have covered will guide you on how to fix binoculars with double vision. Overall, if you are wondering, can binocular double vision go away on its own? It cannot. It is something you will have to fix by adjusting the binocular prisms.
About The Author:
Lake Streeter, A Gun enthusiast, and loves to hunt in the middle of the wood. Always check the latest hunting gears out in the market and try to share his honest opinion with the audience in Hunting Nook.