You have bought your binoculars, taken them out of their packaging, and held them up to your eyes. Now it’s time to make the adjustments needed to fit your personal needs.
The Four Adjustments
There are four adjustments needed to get started. They’re easy. No tools required. I’ll explain each one enough to help you enjoy the best image you can get out of your new binoculars.
1. Eyepiece Spacing
It may surprise you to find out that 90% of new binocular owners fail to take this first step. Take a glance at a few descriptions, and then follow the quick and easy steps to properly make adjustments.
- IPD – The distance between our eyes and the eyepiece is known as the interpupillary distance (IPD) which varies among users. The IPD average length is around 65mm for men and 62 for women, with a range of around 52mm to 78mm.
- Hinges – Some binoculars use a double-hinge system, one on each side of the barrel, connecting to the bridge, while most use a single hinge in the middle of the bridge to connect the barrels. The advantage of the double hinge is their ability to fold up smaller than a single-hinge system and provide for IPD’s as low as 40mm.
- Vignetting – the distortion of light which may cause your image to be blurred around the edges, often referred to as “cat’s eyes”.
Steps for Adjusting IPD
To make this adjustment, you’ll move the barrels closer or further apart until the two separate images in each barrel come together to form a singular circular field of view. By doing this you reduce vignetting and get a crisp, clear image. If provided, you might want to note the IPD scale. Don’t worry if you can’t. It won’t be long until you can make this adjustment in a matter of seconds.
It would be nice if all manufacturers listed the maximum and minimum distance that their products adjust to. But they don’t. So, to avoid the issue of improper fit, you’ll have to go into a shop and try them for yourself.
Eyecups help to keep out annoying sidelight while making sure your pupils are the right distance from the eyepieces to give the full field of view (FOV). Most аrе made of рlаѕtіс, but some high-end binoculars will use mеtаl instead. Rubbеr coverings over the eyepieces are used for adding comfort and to help them last.
Eyecups vary in style and purpose. Roll-down, (found mostly on lоw-budgеt bіnосulаrѕ), pop-up, and twist-up eyecups are common on most binoculars today. Less common wrap-arounds come in winged or horned styles. While not to be used with glasses, wrap-arounds provide protection against wind and block out distractions from your peripheral vision.
Selecting the Best Height – Unless you’re wearing glasses, or have deep-set eyes, the eyecups should be up, at least halfway. Leaving them down will expose the lens to water, dust, and grit. But, there might be times when you need a wider field of view, and getting your eyes closer to the lens is an easy way to do that.
Another consideration is that having your eyecups in the full up position can lead to fogging if it’s cold. Just lower the eyecups some if you plan to be glassing for a long time.
Steps to Adjust Eyecup Height
To move roll-down eyepieces, simply fold the rubber over. Pop-ups are also either fully up or fully down, but the more common twist-ups give you more choices for adjusting the distance your eyes are from the eyepieces. They might be fully adjustable or come with three height settings. If possible, adjust your eyepieces to about 12mm to 15mm from the ocular lens. You’ll protect the lens while improving your FOV, and reduce peripheral light.
3. Focusing Variations
There are 3 categories of focus systems. The individual eyepiece focus systems, fixed-focus systems, set for a specific distance, and the most common type, the center-focus that includes a single diopter adjustment.
So what is diopter and why is it important?
Diopter – defined as the optical power, determined by focal length.
What does that mean? Simply this, most of us will have at least a slight difference in how our individual eyes see things. Even if we don’t notice the difference most of the time, once we magnify an object with optics, the differences become greater (a fuzzy image), and will probably lead to eyestrain.
In order to adjust for the difference of our eyes’ ability to focus, an adjustment knob or ring, referred to as the “diopter”, is usually found on the right eyepiece, though it might exist as a separate function of the central-focusing system. Diopters in these positions will adjust only the right optical system.
4. Steps to Adjust the Diopter
Whatever type of diopter, look for markings that indicate up and down changes, such as +/-, or more commonly, a scale of 2, 0, and -2. Also look for a locking mechanism, available on some models.
1. Adjust the Non-Diopter Side First
Cover the front (objective) lens of the side with the diopter. If you don’t have a lens cover you can use your hand or cardboard. Select an object, rock, tree branch, anything stationery that is no more than about 30 yards away. Next, bring the object into focus by moving the center-focus wheel.
2. Adjust the Diopter Side
Next, stand in the same spot, uncover the objective, and cover the other lens. Find the same object you just used to focus on. Now, move the diopter ring to bring the object into focus. Don’t move the center-focus wheel. The image should now be sharp when you use both eyes to view it.
3. Diopter adjustment on the center column
Don’t worry if the diopter isn’t on the right side eyepiece. The technique isn’t much different even if the diopter is on the center column. Here’s what you do –
First, cover the right lens with a cap, your hand, or some cardboard, but keep both eyes open. Pick out a rock or anything less than 30 yards away that isn’t going to move. Use the central-focus wheel to bring the object into focus.
Next, move whatever you used to block the lens to the other side so that you see through your right eye. Keep both eyes open, and don’t move from your spot. This time use the diopter wheel to focus on the object you selected earlier.
You can now take away the object blocking the left side. From this point on, the two barrels should stay in proper relation. You should only use the center-focus wheel to focus. However, if you use your binoculars for viewing both at night and day, you might need a slight diopter change. Keep in mind that, like prescription glasses, your binoculars are set for your vision. When someone uses your binoculars they will most likely have to make changes to the diopter.
Individual Eyepiece Focus – Militaries have long loved individual-focus binoculars because they are rugged, simple and impervious to the elements.
Just as the name states, focusing is done on each eyepiece by turning the diopters. The process is basically the same as it is for center-focus binoculars. You just have to do it for both sides. Think of the nuisance this must be, especially if you have to view objects at different distances! Refocusing is generally held to only long or intermediate ranges when absolutely needed.
These systems were focused permanently by the manufacturer, for people with perfect, 20/20 vision. If you wear contacts, have perfect vision, or don’t mind wearing glasses, these binoculars offer a much-desired simplicity and reliability.
Though it may seem like they focus automatically, that’s not the case. Fixed-focus binoculars work because your eyes have the ability to focus on things at different distances.
Prisms are aligned with lenses at the factory to give us a beautiful, crisp image. It doesn’t take a whole lot to knock them out of collimation, giving us a blurry, overlapped or cat’s eye image. Besides the lower image quality, miscollimation, whether vertical or horizontal, can lead to eyestrain and headaches. Fortunately, many manufacturers added screws in the prisms known as prism tilt setscrews. Many people will make adjustments themselves if the misalignment isn’t too great. The process requires patience and a basic understanding of how the lenses and prisms function together. Because of the level of difficulty for these adjustments, I will save this topic for a later time.
Time Well Spent
A new set of binoculars can provide you with hundreds of hours of enjoyment, especially when you have taken the time to learn how to properly adjust them for your individual needs. Once you have taken the steps you’ll realize just how easy they are to repeat, and what a difference they will add to your experience.
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