Scope Eye — Optical v. Functional Eye Relief

Woman holding a bandage and bleeding from the forehead

Eye relief can be more than drops in a tiny bottle. It can be a critical part of riflescope performance. If you hope to fire a powerful rifle without cutting your eyebrow with the scope, you need to understand and employ proper eye relief (ER.) There are two kinds: optical and functional.

Woman holding a bandage and bleeding from the forehead
Minor injuries such as “Scope Eye” aren’t necessarily life-threatening, but the right gear in your pack, including derma-bond, bandages, and analgesics can certainly make them more comfortable.
Optical ER is the distance from the external surface of a riflescope’s eyepiece glass to the outside surface of the shooter’s eye at which the full image transmitted by the scope is visible. In other words, you can see everything without those black, shadowy edges. When you see those, you are either too close or too far back from the eyepiece. Go ahead. Try it. Move your eye close to your scope and watch the shadowy edges close in.

Next, pull back and watch them disappear. Keep pulling back and watch them reappear. You are moving in and out of the scope’s preset ER distance, which can be anything from two inches to two feet. Optical ER is something you cannot adjust. Each scope comes with a preset ER and you have to live with it, or live without that scope.

Functional ER is measured from the rear-most rim of the eyepiece barrel to your brow when you can see a complete a full view through the scope. If you have deep-set eyes and your scope has a deeply set eyepiece lens, functional eye relief can be as much as an inch less than optical eye relief. This is a major contributor to painful “scope eye.” If optical ER is too long, you sacrifice field-of-view. If functional ER is too short, you’ll probably get bashed in the forehead each time you fire a shot.

Wide-angle scopes achieve their wider view by sacrificing a bit of ER. This is acceptable on a light-recoiling rifle, but a hard kicker increases your odds for stopping the scope with your forehead. I’ll gladly sacrifice two, or even ten feet, of FOV for another inch of ER in most scopes because I don’t need to see half a football field around my target animal. I need to focus on the animal—without getting bonked on the brow by my scope when I shoot.

As a general rule, the harder kicking your gun is, the longer you want your scope’s ER. A mere two inches of ER might be plenty atop a .223 Remington, but 3.75-inches might not be enough atop a .30-378 Weatherby Magnum. Most manufacturers build riflescopes with 2.75 to 3.5 inches of optical ER, some as much as 5.3 inches. About right for most common deer and elk cartridges from .270 Winchester through .300 Win. Mag. are 3.25 inches and longer, but take functional ER into account. Things get a little sticky with bigger .300s into the .375 H&H. From .375 on up through the .505 Gibbs, you want at least 4 inches of ER—if you want a scope sight at all.

Flashlight beam being shone through a riflescope to measure eye relief
Shining a flashlight through a scope focuses the circle of light when the paper or wall is at the optical eye relief distance of that scope. Measure from the wall to the edge of the eyepiece barrel to get the functional ER distance.
For obvious reasons, handgun and scout rifle scopes are built with extra-long ER of 10 to 18 inches. To get this they sacrifice field-of-view. That’s why looking through one is like peering down a long tunnel. Even with standard riflescopes you trade field-of-view for ER. The farther your eye is from the scope’s eyepiece, the narrower your downrange view. It’s like peeking through a small knothole. The closer you get to the hole, the more area you see beyond it.

The way you shoot also matters. Stock “creeping” contributes to scope eye. If you get excited while hunting and slide your head farther forward on the comb than you normally do when practicing, you could easily shorten functional ER by an inch. Prepare to bleed. Shooting prone and uphill and you’ll bring your brow dangerously close to your scope eyepiece rim, too. At the same time your butt pad will tend to slide under your shoulder pocket. It’s the perfect set up for a scope gash.

Determine Your Scope’s Eye Relief

Finally, be aware that many, if not most, variable power scopes lose ER as power increases. Watch out for this when buying. Be aware that some manufacturers fudge their ER numbers. You can double check them with a flashlight and sheet of paper. To measure ER, lay a ruler in front of a scope’s eyepiece atop a sheet of white paper on a table. Put a right angle bend in the paper. Now put a flashlight against the objective bell of the scope. Shift the scope back and forth over the ruler until you see the sharpest circle of light on the paper. That’s the sharpest focus and the true optical eye relief. Measure from the eyepiece rim to the paper to determine functional eye relief.

Have you ever suffered from “scope eye?” Tell your story in the comment section.

Veteran outdoorsman Ron Spomer began writing and photographing about wildlife, hunting, guns, optics and all things wild and wonderful waaaay back in 1975. He’s been privileged to have hunted on six continents for small game, upland birds, waterfowl, big game mammals, and — no croc — even some reptiles. From the Arctic to the equator, from mountain tops to ocean marshes, Spomer celebrates our hunter-gatherer heritage. You can see him on his You Tube channel and follow him

The Mission of Cheaper Than Dirt!'s blog, The Shooter's Log, is to provide information—not opinions—to our customers and the shooting community. We want you, our readers, to be able to make informed decisions. The information provided here does not represent the views of Cheaper Than Dirt!

Comments (15)

  1. I have technical questions about how to check for ER. Do you set the scope on max magnification (I have a 3.5 X 10 scope). When shinning the light into the scope there are a least 2 rings shown on the paper. Which ring (Inner or Outer) is the one that you need to check for sharpness. Also, I noticed moving the flash light forward and backward will change the image too. Where should the flashlight be positioned ?.

  2. I contracted a nasty case of scope eye back in 2006 or 2007. I mounted a nice little Leupold VX-3 1.5 – 5 x 20mm scope on my shiny new CZ 550 Safari Magnum with European stock, in .458 WinMag. I had the rather silly notion of using it on a bison hunt. The second shot I fired from the box of Haornady Light Magnum 500 grain soft points whapped me good, right in front of lots of my friends. The scar healed rather nicely, never quite got the blood stains out of that tee shirt though. Needless to say I worked up some handloads for this rifle, although I must say, this rifle is NOT my favorite rifle to shoot off the bench.

    I ended up taking my bison with a Remington 700 Classic in 8mm Mauser with 180 grain Barnes TSX all copper handloads. I couldn’t get close enough on the opening shot to be confident of hitting the animal in a vital spot, as these critters in this herd were pretty wary.

    Absent the need for a hunting rifle with real stopping power, my big .458 is now mostly a curiosity that I toy with from time to time. I’m thinking of taking the scope off of it since I can probably do as good or better with open sights at any range I care to take a shot at something with this gun.

    Live and learn, and have fun doing it; we only get to do this “life” thing once!

  3. I’ve had scope eye and blood from a 12 gauge Shotgun that I deer hunt with in NJ (Rifled barrel and Magnum Sabot slugs) that I purchased used….probably why the last owner traded it in . The fix could have been to replace the scope, but I went for a simpler solution. I couldn’t find a commercially available eye shade (Similar to ones I’ve seen used on competitive rifles that is used on peep sites) for my scope, so I built one from black foam pipe insulation and it works fantastic (It maintains min. distance and is soft if it hits you)! Now lets try to convince the scope manufactures to offer a factory soft rubber rear eye shade for their scopes and scope eye will be a thing of the past.

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  4. Many years ago, I needed to bench rest an eight and one half pound Mauser .458 for accuracy. I used a picnic bench rather than a stool ( the recoil took me back over a foot with each shot). On the first shot the scope touched the hairs of my eyebrow. I won’t say I was scared but that critter had my full attention. It took four shots to hit the x ring, we went to a fresh target and I fired a three shot group almost exactly one inch across. My boss suggested we make a sight correction and try again. I made a couple of rude suggestions and announced that I was done for the day.

  5. Everyone with experience letting some shoot through a scope needs to ask them first if they have shot a high powered rifle with a scope. Never assume they have. I did with a young soon to be fighter pilot thinking he had used a scope and he hadn’t an got the crescent moon scar. I felt even worse when his plane went down in gulf war, he didn’t survive, so never assume.

  6. The first time I hunted elk, I was so intent on the target that I moved my eye right up too close to the scope. I ended up with a small gash between my eyes, when the 450 Bushmaster kicked. My guide called it “magnum eye,” but “scope eye” seems a better, general description.

    Now, I check eye relief every time I mount a scope, and I have gone to cantilever mounts on some of my rifles.

  7. I am sporting (what I choose to believe is) a very handsome scar from a scope cut obtained shooting deer from a tree stand using 12 ga slugs through a pump. Apparently not just shooting uphill can give the unwary a kiss! Obviously found myself leaning down and into the scope too much in the heat of battle – but the broader point for fellow hunters with presently pristine brow-lines is we get twisted into all kinds of unnatural positions in tree stands, given the generally uncooperative nature of deer, and its worth checking yourself before the scope does it for you!

  8. Thank you for a informative article written in a way that even a beginner can easily understand.I’ve been shooting for over 50 years and I learned a few things from your story.
    Sam,s elitist comment about learning to shoot with an iron sight is just what we don’t need.Some people are not gifted with perfect eyesight and are manor woman enough to admit a scope will ensure a clean shot on target or a humane kill.Leave your ego out of the shooting sports and try to help those that need it.Our sport is in serious trouble from the morons who think a gun free country is a safe country!
    Thanks again Ron for a great article!

  9. I agree with Sam that you should have the skill to shoot an animal within 150 yards. But, open sites for people like me, with far and near sighted eye problems are difficult to use. I am unable to focus on the front and rear sites at the same time and still see the target.
    So for me, open sites are mostly a best guess shot. That is why I was very happy that some states allow one power or red dot scopes on muzzle loaders. This allowed me to have the same shooting level as someone with good eyesight.
    My brother was hit in the eye with the 3X9 scope on my 30-06 rifle. He had only used open sites and had never used a scope before. But, we did not think that he would get a clean shot with his 30-30 with open sites at a deer that required a 45 degree upward shot with his gun based on the visual distance to the deer.
    He chocked up on the scope like you would do with binoculars. Maybe he could have gotten away without getting hurt, if it had been a horizontal shot. Needless to say, that our hunt ended with that shot. And, luckily he missed the deer.
    Until that accident, I had never heard that your scope could hit you in the eye. With my current knowledge, that accident could have been avoided. He took five minutes to take the shot, since he had difficulty is using the scope–plenty of time to see that he was at risk of scope recoil.
    I bought three rifle scopes last year. I wish that I could have read the above article before making those purchases. Now I have to look at all three guns and determine if the scopes need to be remounted, and how safe they are to shoot.

  10. The Leica scopes have a true, reliable eye relief of 4 inches. The specs are real, not exaggerated. The images are so clear and bright I never need to get too close. The optics are spectacular. I love my Leica scopes on my .223 and .308.

  11. This is a very informative and well-written article – especially informative for those who are new to the shooting sports. I know of another way to completely avoid “scope eye.” It’s called learning good marksmanship with open sights. If you can’t hit deer-sized game at 100-150 yards with open sights, then that should tell you something. There is no substitute for learning good marksmanship, as anyone who has been in the Service knows.

    1. I can see very well out to at least 300 – 400 yards, no problem. Haven’t tried further, but the specs on the scopes are good to at least 1000.

    2. I’m well past the 65 mark and know first-hand the difficulties that come as we get older, with declining vision probably topping list. But I’ve learned along the way that adapting is probably the best option. Having a sound basis in good marksmanship can significantly aid adapting.

  12. I have never had scope eye, but I am careful about scope mounting. I make sure the scope is not mounted too high or too low causing cheek anchor issues. and as for serious magnum caliber rifles 300 win mag to .375 H&H mag I make sure the rifle is weighted enough to mitigate felt recoil, lugging a heavy rifle is the price you have to pay for long range and heavy power and still have a flinch free rifle.

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