The eye relief of a scope is the distance from the lens your eye needs to be to get the full image from the scope. Any further back or forward and you lose some of your visibility. The best way to measure it depends on why you’re measuring it in the first place.
Most sights will have their eye relief posted on the manufacturer's website or on the product page where you bought it, so if you’re just trying to remember what it was, you can usually find out that way.
The other way to semi-accurately measure it would be to get it mounted on your rifle, position your eye to where you can see the whole image, then hold a tape measure or ruler to measure the distance between where your eye is and where the eyepiece is.
Measuring eye relief can be insightful if you’re trying to decide on purchasing a new scope and you want to compare it to something you’re used to. If you know, for example, that your scope has 3” of eye relief (meaning your eye needs to be 3 inches from the lens), and that it sometimes feels too cramped or you’ve gotten hit by a scope bite, then you can probably guess that a scope with 3.5” or 4 inches of eye relief would be better.
Measuring Eye Relief - The Details
Especially on cheaper scopes, the published eye relief may not be accurate. In cases like these, especially when your experience with the scope seems not to be in line with the official specs, it can be good to measure what eye relief you’re actually getting.
If you are used to cheap optics, it’s easy to develop an attitude of “more eye relief is always better”, but in reality it’s just because you’re used to scopes with short eye relief. Any more than ~4.5 inches and it can start to be difficult to get into a comfortable shooting position unless you make the jump all the way to scout scopes, which will usually have between 7” and 9” of eye relief.
If you want to know real-world eye relief that you’re getting out of the scope you have in your hands, then the only real way to know for sure is to get a tape measure and have someone measure the distance from the lens to your eye while you hold still.
It’s tempting, especially for new shooters, to hunch in towards the rifle scope rather than take the steps to adjust eye relief. This results in more scope bite. The industry average eye relief for rifle scopes is 3-4.5 inches. Rather than getting in closer to the scope, focus on making sure you can see the entire field of view.
Eye relief is the point at which you can see the whole picture.
When You Want Less Eye Relief
There are lots of cases where you might want a small amount of eye relief on your rifle scope. If you are shooting a smaller rifle like a .22 rifle that does not have an adjustable stock, you may need to get closer. Military-trained shooters who shoot NTCH (nose-to-charging-handle), often want scopes with shorter eye relief because of their shooting position.
If you wear glasses, that can affect the standard eye relief that works best for you. Scope manufacturers usually have different rifle scopes with different standard eye relief that are specifically marketed towards specific use cases.
When You Want Long Eye Relief on a Rifle
Long scope eye relief is most important when you’re shooting a rifle with heavier recoil. When you mount the scope on the gun, make sure to adjust the rings so that the eyepiece is in the best place for your eye.
What Is Scope Eye Relief and How Is It Adjusted?
Eye relief is an important rifle scope specification. It determines where on the rifle the scope needs to mount in order to give the shooter a comfortable shooting position. Remember, eye relief is the distance that the pupil of your eye needs to be at in order to get the entire field of view without any clipped images out of your scope.
You can’t really adjust the eye relief on a scope. It’s best to get either a long eye relief or short eye relief scope based on what you’re shooting and how you like to shoot. What you can do is adjust where the scope itself is mounted away from your eye. If you aren’t getting a comfortable position with where the scope is mounted, go through the process of adjusting the scope rings.
You can tell that you’re not within the eye relief of the scope if the image is blurry, out of focus, or some of the field of view is obstructed by the scope itself. Many hunters prefer a long eye relief scope since they’re typically shooting bigger calibers with more recoil. You’ll want the right eye relief for your rifle, no matter what you’re using it for.
If you’re making adjustments to where the rifle scope is sitting to get good eye relief on a rifle, then start by getting in a comfortable shooting position. Hold the rifle into your shoulder, and lower your head to line your eye up with the rifle scope. Make sure you’re comfortable.
If you already have the rings loose, have a friend slowly slide them forward or back until the scope eye relief lines up with your eyes. Then tighten the rings to the base and you’re good to go.
Other Extremely Important Scope Specifications
Eye relief is not the only thing that matters. There’s a lot more to how a scope operates.
Light transmission is a measurement of how much light the scope allows to pass through the exit pupil and into your eye socket. A few things play into this, but it’s mostly the quality of the lens elements combined with the size of the objective lens diameter and coatings.
As you increase magnification, light transmission goes down, and you may have to adjust eye relief if you plan on shooting at the longer end of the magnification range of your rifle scopes. This is an important consideration depending on what kind of shooting you’re doing. If you’re just hitting the range in daylight, then a scope with less brightness isn’t a big deal.
But if you’re shooting in dusk/dawn or other dim situations, being able to see the full field clearly is a good idea, and should be at the center of your thought process. Is eye relief important? Yes, but so are a lot of other things.
Magnification is a tricky thing, since it involves bending light. High magnification bends a lot of light and can interfere with getting a clear picture. If you wear eyeglasses or use binoculars, you probably have experienced this before. Particularly around the edge, the image can get distorted.
High magnification also shortens eye relief in some cases, depending on the scope. You may want to expect to adjust your position depending on what power you have the scope set to, especially if it’s long range. Image clarity issues like color accuracy, chromatic aberration, etc. can also be affected by this.
Field Of View
Field of view is a wonderful thing. When you have a full view of a clear field and can see more of the surroundings of your target, it’s so much easier for most people to get their sight picture, focus on the target, and nail their shot.
Field of view refers to how wide the image through the scope is, and while it’s affected by magnification, you can have two scopes with identical magnification but vastly different fields of view.
Why Eye Relief Matters
Proper eye relief can make a rifle scope, while not having adequate eye relief can break a rifle scope. Long eye relief scopes can help prevent scope bite, which is a painful way to learn exactly what recoil feels like. The eye relief on a rifle scope is an important specification to consider.
If you are shooting a rifle with heavy recoil, for example, the recommended eye relief distance is going to be longer than for a rifle scope that’s going on a smaller caliber weapon.
Eye relief on a rifle scope isn’t something you can make adjustments to, but even though you can’t adjust eye relief, you can still measure eye relief and adjust the position of the rifle scope lens on the rifle you want it to mount on. It’s a straightforward process to adjust the rings.
A long eye relief scope can be great for large calibers with strong recoil, and it’s usually a simple process to adjust the rifle scope forward on the rifle to get the eyepiece a comfortable range away with the stock tucked into your shoulder. Since eye relief is the distance your eye has to be from the ocular lens, you can’t adjust eye relief.
But you can adjust the scope and rings to make it work for your eyesight. Have you done this process before? If you have, feel free to explain what worked best for you in the comments. Our goal here at the Hunting Mark is to help everybody get a little bit smarter and more responsible with their firearms, and your input can go a long way in helping accomplish that.