What is Eye Relief and Why is it Important?

What is Eye Relief

What is Eye Relief??
(and why you should care)

When it comes to the inner workings of a rangefinder or other magnification tools, such as a scope or binoculars, many people don’t truly understand what the reported statistics from the manufacturer mean or how those statistics will benefit or affect them in their use of the device. The problem with that being, those stats control how well the device works for various purposes and when you understand some of those important stats, it can help you make the best selection for your needs.

One of those mystery stats is that of “Eye Relief;” and rather than make everyone re-read this explanation in every review, we’ve decided to clear this up in one article and then those who wish to read about it are free to do so and we’ll stop boring everyone else.

Unless we're talking about rifle scopes, the people who should be most interested in eye relief, are people who wear glasses, although users who don’t wear glasses will benefit as well.

Eye relief, is the distance that your eye needs to be from the eyepiece of the device you're using, in order to see the full field of view without any blockage or shadowing. We’ve heard people in general conversations discuss the fact that they think you shouldn’t buy a device that has “too much eye relief” because that causes a blocked view. That's an interesting thought, but they don't quite understand.

Every single magnifying device, can have too much eye relief or too little eye relief, depending on where YOU place YOUR eye.

The distance that is required for proper eye relief will be different for different rangefinders based upon their design. In order to determine the correct distance for your device, you would need to read the manufacturers specs. Don't panic... we didn't just tell you to read instructions, only the specs. 

Each device has its “ideal” eye relief distance and most manufactures will tell you what the distance is for that particular device. They'll either convey it in terms of Millimeters (mm) or for most scopes you will see Inches (In).

Having a device that has a longer eye relief, is not a problem at all, in fact, it's desired. It's when the user, places their eye closer or further away than that ideal distance, that they run into problems. 

Eye Relief with Glasses

When a magnifying device has a very short eye relief, (we'll say less than 15mm) that means that in order to get a good view of things, you have to get your eye really close to the eyepiece.

As that eye relief number increases, you are able to see a full field of view with your eye further away from the eyepiece.

So for instance, if the specs of a device say that it has an 8mm eye relief, that means that for the best view, your eye would need to be 8mm from the eye piece. If instead, it says that the eye relief is 16mm, then to get the best view, your eye should be 16mm from the eyepiece.

If for some reason, that information is not available, you would position your eye at a particular distance from the eye piece and notice whether you can see a clear view. You would then move closer or farther away until you no longer had any blockage or shadowing anywhere around the field of view.

This blockage or shadowing is called vignetting.

In photography, vignetting is often used on purpose to give style to a photograph, but when it comes to magnifying our view for hunting, target practice, bird watching etc… vignetting does not equal a beautiful picture.

The blockage can happen just along the bottom, along a side, or around the entire circumference of the view.

Here are some examples:

Clear Field of View No Vignetting

Full Field of View

This is our starting point and our goal, Clear Full Field of View with No Vignetting. 

If you have your eye the correct distance from the eyepiece, this is what it should look like.

Vignetting

In each of these below examples, notice that some portion of the field of view is blocked or reduced.

Crescent Moon Vignetting at Bottom
Vignetting Entire View Reduced
Crescent Moon Vignetting at Side


If, when you look through the eyepiece, you notice the vignetting creates a crescent moon shape toward the bottom or sides of the field of view, then you have your eye too close to the eyepiece and should move further away.

If the vignetting or shadowing appears around the entire field of view, or you notice it appears as though for some reason you have a smaller field of view, then your eye is too far away from the device. Just re-position your eye either closer or farther away until you can see the full field of view.

How Eye Relief is Affected by Glasses

With devices that have shorter eye relief, (again, we'll use less than 15mm as a pin point) people who wear glasses will often have trouble with vignetting or shadowing that restricts the entire field of view, because they cannot get their eyes close enough to the eyepiece to obtain that clear field of view.

For people who don’t wear glasses, longer eye relief can still provide a benefit, as they can more quickly see the field of view without having to get the optics all the way up to their eye.

The absolute minimum eye relief needed for someone who wears glasses is 15mm and that’s not great, it will just work. Really, we'd rather the eye relief be over 16mm, but 20mm or more would be fantastic.

If you would like to check out a rangefinder with LONG eye relief, and we're talking about 24mm eye relief, look at the Sig Sauer Kilo850!

Scopes

Regardless of whether you wear glasses or not, eye relief becomes even more critical for everyone when you’re looking at rifle scopes.

Anytime you’re putting your face close to a firearm, you need to be aware of RECOIL and you want to be extremely cautious!

Just ask the many fine folks who have ended up with cuts above and around their eye because they got hit in the face with the scope when the gun recoiled. NOT PLEASANT!

Scope Eye Relief

Normally speaking, the eye relief for a rifle scope is going to be around 3 ½ inches or more. We’ll save you from having to do the math; at 3 ½ inches that would be the same as 88.9mm. Compared to what we were just discussing above, 3 ½ inches might sound like a lot, but when you're talking about scope eye relief, it's really not.

Firearms have recoil and some have more than others. If you are using a firearm that has ALOT of recoil, you're going to want ALOT of eye relief! 

So if you are looking at a scope that only has a 3 ½ inch eye relief, you better be putting it on something that doesn't have much kick.

This distance should not be an option, it should be required! That is, if you want to have good and safe results.

There are some devices that will actually have an adjustable eye relief, where by turning in or out the optical lens, the user can increase or decrease the eye relief distance.

Other devices will have an eye cup that can be folded back in order to give users who wear glasses the ability to get their eye closer to the device.

But overall, what is important is that you just learned something new and with this new found knowledge, hopefully you will be better prepared to make educated purchasing decisions regarding the magnifying tool you intend to purchase.

We hope that this explanation helps you to understand eye relief a little better and why this stat is so important. 

Happy Ranging and we hope to spot you again soon.

Resources:

Wikipedia

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