Can someone explain about eye relief.

[Drift]

I know what it is. What I want to know is how it fits into the relationship between magnification, and what ever else (like tube diameter or perhaps scope length or maybe bell diameter ?). And how do they figure out how "big" an eye box is anyway?

[grayfox]

I'm not a designer, but eyebox is the range in inches, between which the near glass... the ocular lens, is fully expanded to the eye. the view fully takes up the area inside the circular edge of the lens. if you go closer or farther then the viewing window shrinks. Like, 3.2-3.9"...

[Bearcatrp]

Grayfox is spot on. This may help, look through your scope. Then move closer then farther away. To close and you see black around site picture (end of tube). Back off until sight picture fills. Worked for me mounting my scopes over the years. Am sure others have there own way of doing it. Hope they chime in to help.

[JASmith]

Having once gotten a mild case of Weatherby eye (with a Weatherby no less?), I use the moving eye back and forth technique too.

I try to mount my scope so my normal head position is as far away from the scope as possible while still getting a full image in my vision.

[Randy99CL]

A few weeks ago I took my new rifle and scope into Sportman's Warehouse to buy rings. The guy at the counter had never seen anyone close his eyes to check the eyebox before.

If you're not aware of it, the best way to check scope position (fore-aft) and ring height is to cheek the rifle with your eyes closed. With no distractions make sure the stock position feels right on your cheek, arms are comfortable, etc.
When you open them the sight picture should be perfect.

When we shoulder a gun with eyes open we have a subconscious tendency to adjust our position to make it work.

[Kswhitetails]

Randy, I use this method for everything I do when I put my optic on my guns. I get close, then start closing my eyes, counting to a slow 10, and opening exactly as you describe to determine what changes I need to make to scope. The position, the ocular focus, etc. It's important to keep your eyes "fresh" when setting things up so that it's as close to the natural position as possible when you get things torqued down permanent like. We do indeed get too much of our heads into our optics... it's distracting!

[JASmith]

Dang, I keep forgetting to close my eyes.

I will be more attentive to this detail next time. (I hope!)

[Drift]

I know that at higher magnificatons I have to put my eye closer to the scope. I dont know why that is. I know that scout/pistol scopes have a very long eye relief and FOV is very small even with low power. I dont know why that is either. There is a whole science of optics that I am sure explains all that; along with some formula dictating the size of the eye box. I just dont know where to look them up.

[LRRPF52]

Eye box is exit pupil, not eye relief.

Exit pupil is the cone of light transmission that is available at or behind the eye relief.

[Klem]

I know that at higher magnificatons I have to put my eye closer to the scope. I dont know why that is. I know that scout/pistol scopes have a very long eye relief and FOV is very small even with low power. I dont know why that is either. There is a whole science of optics that I am sure explains all that; along with some formula dictating the size of the eye box. I just dont know where to look them up.

Strange...Eye relief should not change as you crank up and down the magnification. Eye relief is a fixed distance engineered by the manufacturer to be the average cheek-weld on the average stock. You should still be able to shoot pushing your head forward and back on the stock but it won't be optimum. Smaller field of view if further way and the risk of 'sniper-eye' if you get too close. Eye relief is less forgiving to a slack cheek weld the higher you crank it up as the field of view gets narrower. Sounds like your scope might be a little too forward on your gun if you have to push your head forward on high magnifications.

As I understand it, exit pupil is the diameter of field of view at the manufacturer's eye relief. It is calculated by dividing the objective lens by the magnification. 4.5mm is daylight retina expansion while at nighttime they expand to about 7mm (i.e 7x magnification with a 50mm objective lens or 6x with a 42mm objective is the brightest field of view you will get when night hunting. Any higher magnification than that and it starts to get darker with less resolution)

[Kswhitetails]

Go ahead, Mr Smith, make fun. It makes a difference for me. I tend to get overly focused in and make things more difficult because I'm thinking of how to make it perfect rather than just letting it happen naturally. It's actually surprising how much easier keeping your eyes closed makes things just fall into place. But eye understand your jab...

I find closing my eyes especially helpful for setting a reticle's focus (Diopter) correctly, which tends to be the foundation of most folks scope issues in my experience. I recently joined a shooting club and have been exposed to more new friends to shoot with, their gear, and the place we gather in to do so. I've been picking up and handling optics for a a few years, but have educated myself in crash-course style especially in the last couple months at the range and at competitions because circumstances put me in the market for several new optics all at once. At the club, I was always watching and asking to play with cool scopes - whenever guys that have something I've never played with let me get behind them. I've shot behind a NF ATACR, NF NXS, and a Kahles 318i recently. I've looked through a Vortex Razor GII 4.5-27, SWFA 3-15, SWFA 10x fixed, Burris XTR IIs, Bushnell 6500 elite 4.5-30 and elite tactical 3.5-21 (several models), Bushnell LRTSI, Bushnell XRS II, etc (I have an LRHSi 3.5-18x44 on the way - I've read several people comparing these to the XRSII, I'll believe that when I see it for myself...) And just today a Leupold Mark 5 HD 5-25x56 H59. (insert hallelujah music) So I have become sort of an optic-snob-come-lately... Caveat - FOR THE LOVE OF GOD, DON'T LOOK THROUGH ANY OPTIC YOU CAN'T AFFORD TO OWN. It's a dangerous situation! Use extreme caution because it makes one realize everything you've been missing all this time, which creates a painful struggle within one's self to decide how long one is going to live on bread and water (for the next six months) in order to spend the lunch money I've been saving on a scope... Ahem...

I'm surprised at the number of new scopes that grace the range owned by guys (Hi, my name is KsWhitetails. HI KSWHITETAILS. I'm a recovering optic idiot.) that are convinced the scope they had before (usually something in the order of a 400 dollar Leupold or Bushy or Burris) was better than the $1000-$2500+ optic they just mounted up to come out and play with. They buy - usually based on internet reviews, which concretely convinced him/her that the optic will pretty much be set up pretty close to perfect out of the box, and are disjointed when they get to the range and can't find the correct parallax setting. (the problem is they think parallax sets the images focus, which it does slightly effect, but which isn't really true...) They are worried because the image doesn't "pop" or look as good to them as the online reviewers said it would be... When I get off the scope, I have actually had two guys come up to me later wanting to know how I made their issues go away. (All I did was set the ocular focus to my eye) Setting up an optics eyepiece, especially optics sensitive to diopter changes like rifle scopes and binoculars, is really easy if you know how. The real problem is most just don't seem to know how. Well, they don't REALLY know how. They can fiddle with it and get close, but they can't tell you why what they did worked, and thus, cant replicate it when the setting changes. I used to be this guy. Ignorance is bliss indeed, but it's expensive...

I can't tell you how many times recently I've read blog posts or articles by supposedly knowledgeable folks, and been wondering how many are led astray about using the parallax wheel to set focus because they say things like parallax and focus in the same sentence as if one has much to do with the other. Hocus Focus, that is.

I would explain what I have learned to do, but rather than make this longer: Here is a pretty good post on it. http://www.accuracy-tech.com/ocular-...ax-adjustment/

While it's true that the Parallax can change the image clarity if things aren't set up correctly, if your ocular lens is in focus correctly, you shouldn't notice it. Especially on higher end optical sights.

To the OP's question, "eye relief" refers to the distance (a range) between the ocular scope lens and the lens of your eye. You must must be within this range correctly to see a correct sight picture through the lenses within the scope. This is always set by the manufacturer by how they designed the systems lenses; small angles between the innards change this dimension quickly. The ocular lens has the absolute most to do with it as it is the last lens the light travels through to reach your eye.

"Eye box" is a similar term but includes both distance from the ocular longitudinally (how far your eye is away from the lens), as well as horizontal and vertical variance. Hence, it creates a sort of 3D "box" of space (actually an egg shaped space behind the lens) that your eye must be within to gain the correct sight picture. Optimally, you want your eye to be centered in this space to ensure lack of mis-allignment, creating angular discrepancies in your aiming points. (Okay - this is actually the definition of parallax; and when you're not properly inside this box - IE, off center, left/right/up/down, or too far forward or back from the optic, you see blackened edges or an obscured visual image. This is typically referred to as "tunneling" or occlusion) When you read someone comment on "how forgiving the eye box is", what they're referring to is how large the eye box is and how easy it is to find the center of it with your eye when behind the scope. This is not always the case among optics, some of which have very small voids in space where your eye must be to gain a good sight picture; Which complicates most everything about using the optic. There are some that argue that a small eye box is actually a good thing as it forces the shooter to center their eye in the optic, thus forcing consistent aiming alignment with each approach to the scope. I tend to disagree as I believe that if it's made right, (and set up well,) a very forgiving eye box is just as accurate as any that are pain in the butt to align, and are much easier to get good results from; therefore they are much more enjoyable optics to use correctly.

The size of the tube of an optic effects several things, but has little to do with eye relief; It effects mainly the elevation and wind-age dial ranges (bigger inside diameter means more travel to put more clicks on the dial); as well as the amount of light allowed through (optical transmission, or light transmission); and larger, thicker pieces of glass. Usually, the larger the glass, the more light and thus the better the image that can be captured and transmitted. This has been pushed upward (34, 35, 36, 40mm!) in the scope market due to the demand for more robust optics, and more available elevation on the dials. It does also allow more light through, a function called aperture. The size of the tube has little to do with "eye relief", except when it changes the ability to align the lenses in a different configuration; though this is still just a decision made my the manufacturer and can be done the same way in a tube of a smaller size, for varying cost. Smaller spaces are more difficult to fit things into... Typically, a larger tube allows a thicker wall as well, making an optic potentially stronger for the intended use.

In a well made optic, zoom should have no noticeable effect to eye relief, but it will effect the eye box because it lowers the width of exit light of the image. This is called the exit pupil if I understand it correctly. Exit pupil is the diameter of the light cone at the given eye relief distance. A scope shouldn't change how far from the lens your eye is when you zoom in, only that the exit pupil decreases - which means it becomes harder to remain centered in the image properly because it decreases in diameter with the decreasing exit pupil.

How do they figure out eye relief? They use a long string of simple angular calculations generated by the varying curvature of the concave or convex lens sections within the scope to determine the exact point that the image should theoretically enter your eye's lens. Follow the red lines on the image.

http://www.thetruthaboutguns.com/wp-content/uploads/2011/06/Telescopic_sight_internals-600x195.png

Seriously, JAsmith - try closing your eyes. Place your rifle on your shooting platform, get behind your scope, and close your eyes. Now, get comfortable. Then count to ten, and open them into the ocular of your scope. Those four seconds in which your eye is attempting to focus into the lens will illustrate a lot to you. If you can't open your eye and see things correctly right away, and it's taking more than a few seconds to get the picture right, or if you're moving your head to get it right, then change the scope or stock adjustments accordingly. You want to see well when you open your eyes, right? Set up this way, you will likely find it easier to get your eye properly aligned; And into the "eye box" and have a constantly crisp reticle - despite the zoom level, the parallax setting, and the lighting conditions, making your rifle and scope seem like it's made just for you. Which of course, it should be.

[biodsl]

Strange...Eye relief should not change as you crank up and down the magnification. Eye relief is a fixed distance engineered by the manufacturer to be the average cheek-weld on the average stock. You should still be able to shoot pushing your head forward and back on the stock but it won't be optimum. Smaller field of view if further way and the risk of 'sniper-eye' if you get too close. Eye relief is less forgiving to a slack cheek weld the higher you crank it up as the field of view gets narrower. Sounds like your scope might be a little too forward on your gun if you have to push your head forward on high magnifications.

Klem...I know nothing about the science behind this but look at the specs on any variable scope and you'll find a range for eye relief.

[JASmith]

Kswhitetails, I was, and am, serious -- I intend to close my eyes when I try to set the next scope.

The advice is sound, and is something I should have known for a long time but did not.

I do know that one should focus on a distance object or the sky before checking the focus. The reasoning is similar -- one wants the eye's focus to be as close as possible to a natural state so no time is lost to the conforming to an improper focus.

When setting the position of the scope, one wants the pupil to be as large as practicable. A smaller pupil could allow the position to be a bit off of optimum.

Yes, I understand, and your posts did "open my eyes" to a new approach.

[Randy99CL]

I knew I'd seen a lot of scope spec sheets that listed different eye relief dims according to magnification, so I tried Leupold and found this: https://www.leupold.com/scopes/rifle...rk-5hd-5-25x56
On this scope it changes from 3.58" at 5x to 3.82" at 25x. Less than 1/4".

And thanks KS for an informative and interesting post.
I've seen/heard many times that you have to close your eyes before adjusting the ocular for reticle focus. You can't look at it for more than a second or so before your eyes will try to adjust.
I've worn glasses for more than 50 years and first noticed that affect when I was young; when I was getting fitted for glasses I could see my focus shifting trying to correct for whatever lenses the doc had me looking through.
Totally automatic and impossible to control.

[Kswhitetails]

JA- Haha I read your post and thought you were making a pun about the distraction line...

1 - run mag all the way up. You want to focus the reticle at maximum magnification. That way, no matter where you are in the rest of the mag range, you're sure to have it right. A lot of folks I've met don't do this, and wonder why the reticle goes blurry when they zoom into a distant target...

2 - I find it best to do it against a bare spot on a white or beige wall, something free of distraction. A light blue, cloudless, birdless, wireless, tree branch free sky works too. It just needs to be an artifact free, monochromatic view. Theoretically, it should eliminate your eye's tendency to try and focus on the reticle, IF you can practice the skill of trying to focus on the wall/sky (out to infinity) instead of the reticle. The idea is to set it by looking through it, not at it. This is where closing your eyes really comes in nicely. As soon as you see yourself trying to focus on the reticle, close them, and turn the diopter a little further. Count to ten, and open them. If it works, you can just tell, and it'll be something you'll always know from now on.

3 - don't get frustrated. If it gets difficult, walk away. Do something else, come back later, tomorrow. This is the foundation upon which the rest of the set up is based. Nothing works well with a half set ocular lens. If you're at the range, remember. Close is close. It will get the job done well enough. But perfect is a whole new world.

(Tip - if you don't have a locking diopter adjustment - witness mark it once you've found "perfect" for obvious reasons...) I use the tip of an xacto and score the rubber ever so slightly if there isn't a dot molded into it - it doesn't have to be deep, you'll know what you're looking for next time you need it - because paint rather quickly comes off the rubber eye piece ring, especially when you sweat on it and wipe it off; and scratch the tube slightly with the same.

Randy, the whole reason these things are adjustable is so that people that have less than perfect eyes can set them up to be able to see. I've read a couple of F class guys or some such that wore glasses their whole lives - and when they shoot, they remove their glasses because they have set their scopes to their shooting eye. They theorize the extra lens interferes with truest parallax adjustment. They also find their new bifocals distracting... I don't know if that's true or not, but it works for them...

I think what's most important is the mageek off dis tink calt CONSHISTNCIE...