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Thread: Help me understand eye relief on a scope.

  1. #1
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    Help me understand eye relief on a scope.

    From what I understand, "eye relief" is the maximum distance between the eye and the scope. Granted on high recoil rifle, it is good to have a large eye relief to keep your eye a safe distance from the scope.

    However, what I don't understand is the measurement between the eye and the minimum distance from the scope where the full view can be seen. Once you establish a minimum distance, you can then take the difference between the minimum and maximum and this is the operating distance where the eye can be and still see the full view in the scope. Is there a name for this distance? Do scope manufacturers adress this?

    It would seem to me that the greater this distance, the better the scope would be in a tactical situation i.e. you quickly raise the rifle to your shoulder and establish a shooting picture.

    So I have ring around the collar? i.e. is my head up... Can anyone explain this to me?

  2. #2
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    You have eye relief on one side of the coin and field of view on the other. You give up field of view for eye relief and vice versa. Eye relief is a really a focal point away from your eye measurement.

    The ring on the scope is focus on ajustment not a focal ajustment. It helps to adjust the scope to you eye and is more diopter than anything else. It is not ment to adjust your eye relief (not that some minor adjustment may take place as a by product).
    Last edited by Uncle fuzzy; October 18th, 2009 at 02:05 PM. Reason: sp

  3. #3
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    The pupil of your eye is nominally 5mm. The exit pupil of the optical devise you are using should match this measurement. In other words the distance that these two measurements are equal in the eye relief. At that distance from the ocular lens (the rear lens) the exit pupil diameter will be equal to the pupil size of your eye. Obviously the lower the ambient light level the more your pupil will be dilated (larger in diameter) and if the exit pupil of your scope is smaller than the size of your pupil, for the distance your eye is from the scope) you will see a ring around the image from the scope.
    Ideally the eye relief should give your eye a full field of view and be far enough away from your forehead to prevent the scope from contacting you during recoil.

  4. #4
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    If you get your shoulder into those heavy recoil rifles they will be less able to get you in the eye area.

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    It would seem to me that the greater this distance, the better the scope would be in a tactical situation i.e. you quickly raise the rifle to your shoulder and establish a shooting picture.
    This...

    FWIW.....
    When setting scope (lap the rings for bearing surface) take up bench position lock in your cheeck rest slide scope back and forth until all "swimming" is removed snug down scope. Test as above ,once satisfied check scope level and lock down...

    Or, go to your gunsmith and have him help you set your scope...

    ST~
    Take your time... Don't live too fast,
    Troubles will come and they will pass....

  6. #6
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    The point of the eye relief is where the image comes in to full focus. Before and after that point the image will not will the ocular lense. That point should be fixed. Then again variable magnification scope makers can save money if it is not. I guess "adressing the issue" has it conflicting interests. Since the shortest eye relief is at the hight magnification, that is the setting you use for mounting the scope.

    Lets adress you other issue some more. If scope X had a an eye relief of 3.5" and a field of view of 25' at 100 yards. Scope Y has an eye relief of 4" and a field of view 20' at 100 yards. You have battle field conditions, as per your question... You now have a target that is closing on your position... At 50 yards you now have to find the target in a 12' window or a 10' window for your shot. They are closing so that you now get a 6' window or a 5' window since you had to hunt for them. It is not JUST about getting the gun up quick it is also about finding the target.

    Does this help?

  7. #7
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    There are also three general categories of eye relief for telescopic sights. Scopes built for mounting in the more traditional position over the receiver we'll call "regular" eye relief, though they vary of course. Scopes built for mounting with the occular lens in front of the reciever ("scout scopes") have "internediate eye relief" (I.E.R. - nominal about 9 or 10 inches) and scopes designed for handguns have "extended eye relief" (E.E.R. - nominal closer to 16 or 18 inches).

    The more the eye relief, the more forgiving the scope in terms of eye position behind the scope. The less magnification the greater the FOV, all else being equal. Hence, your question was answered in part by Jeff Cooper back in the 1960s when he started using an IER scope on an all-around rifle he termed the Scout Rifle. Low magnification and extremely forgiving eye relief allow for rapid target acquisition.

    Your desired application determines the type of optic you'll want. There are of course all sorts of "tactics", so depending on the particular "tactical situation" it might call for a super long range rifle with 20x+ scope or it might call for a carbine with a 1x reflex or holosight, the latter being capable of mounting anywhere along the rifearm, as their eye relief is unlimited. A tactic is a method, so we might call a tactical situation a "methodical situation". Sitting in a tree stand is a "tactic" as is lying on a mountain overlooking a valley with a .50 cal waiting for a jihadist to present himself as a viable target. Nor are optics always needed.

  8. #8
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    "...shortest eye relief is at the high magnification..." Your confusing field of view with eye relief. Eye relief has nothing to do with magnification. It's the distance the rear lens of the scope is from the eye when you can see the whole circle.
    "...the measurement between the eye and the minimum distance from the scope where the full view can be seen...name for this distance?...scope manufacturers address this?..." That's eye relief. Set in the factory.
    Field of view is the width of the area seen with a given amount of magnification. the higher the magnification, the smaller the field of view. It's expressed in feet or meters, usually at 100 yards/meters.

  9. #9
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    The more the eye relief, the more forgiving the scope in terms of eye position behind the scope
    Yes, that is what I'm looking for: "forgiveness". Say at the maximum magnification on an adjustable (or zoom) scope, the eye releif is 3.5". If on scope X, I can see the full image at 3.4" - 3.6" and on scope Z I can see the full image at 3.45" - 3.55". I would prefer scope X, all other things being equal. Is there a term that describes this?

    Incidentally, my friend bought a Mueller Optics 4-16 x 50 AO Tactical scope. http://www.muelleroptics.com/products/MT41650IGR.html and brought it over yesterday to install it on his Savage along with Leupold base and rings. My first problem was that I mounted the base with the screws in the back, I guess I was thinking they were for adjusting elevation or something. The scope wouldn't fit into the rings, so I reversed it with the screws over the bolt. It didn't look good but it fit.

    If you look at the picture of the scope, you will see that there is very little room before the taper on the front of the scope. This meant I only had about 1/4" of movement forward and aft to get the eye relief correct. That was a no brainer. I was feeling quite stupid, but then he put on his jacket and his magnum pad, and tried to weld his cheek to the stock. The pad was inside out. Assuming the old rumor that "God is dead" is false, "Thank you God". I felt better.

  10. #10
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    Your confusing field of view with eye relief. Eye relief has nothing to do with magnification.
    I don't think this is correct. The way I read it four things change when you adjust a variable rifle scope. One, the magnification of course. Two, the exit pupil diameter. Three, the field of view. Four, the eye relief. The FOV, exit pupil, and eye relief increase as the magnification decreases.

    If you look at the specs for a variable scope all four should be expressed as a range (x-x) not as a fixed number altho I have seen a few scopes that claim a constant eye relief but I have yet to look thru one.


    This is the spec for a Leupold VX-3 3.5-10x40. Not a complete spec (got this from SWFA) they left off a few things including exit pupil.
    Specifications
    Weight (oz): 12.6
    Duplex
    Length (in): 12.6
    Eye Relief (in): 4.4 - 3.6
    Field of View @ 100 yards (ft): 29.8 - 11
    MOA: 1/4
    Finish: Gloss
    Ring Spacing
    Max Mount Ring Spacing (in): 5.8
    Front Ring Space (in): --
    Rear Ring Space (in): --

    Another spec from SWFA this time a Bushnell Elite 4200 3-9x40. They include the exit pupil on this one and also claim a constant eye relief. I remain doutful on the eye relief being constant but who knows.

    Specifications
    Weight (oz): 13
    Multi-X
    Length (in): 12.6
    Eye Relief (in): 3.3
    Field of View @ 100yds (ft): 33.8 - 11.5
    Exit Pupil (mm): 13.3 - 4.4
    MOA: 1/4
    Lens Coating: Fully Multi-Coated
    Warranty: Limited Lifetime
    Dallas Jack

  11. #11
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    Yes, that is what I'm looking for: "forgiveness".
    In my experience, the higher the mag, the lower the "forgiveness" (range of eye relief that gives a useable scope picture). It's not usually listed as a spec of the scope.
    scopes designed for handguns have "extended eye relief" (E.E.R. - nominal closer to 16 or 18 inches)
    That is absolutely the "traditional" use of "extended." But some manufacturers use it to mean about one more inch of eye relief on their rifle scopes, for heavy recoiling rifles that might be shouldered in a hurry or while prone (where the forehead can get closer to the scope--don't ask me how I know!).

    For example, the Swarovski Z6 1-6x24 has an eye relief of 3.74 inches, and the Z6 1-6x24EE has 4.72.

  12. #12
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    Eye relief is the distance between the eye lens of the scope and the plane where the exit pupil is formed. To see the entire field of view, the pupil of the shooter's eye must be at the exit pupil of the scope (and the diameter of the eye's pupil must be at least as big as the diameter of the scope's exit pupil). If you move your eye farther or nearer than the exit pupil, less than 100% of the light collected by the optic will enter your pupil.

    Sophisticated and expensive zoom optics can keep the exit pupil stationary at all powers. Others like my not-so-sophisticated zoom spotting scope do not. At 22 power, the exit pupil is further from the scope's eye lens, at 66 power, much closer.
    "If you got to shoot, shoot! Don't talk!" -Tuco Ramirez"

  13. #13
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    Newer scopes, mostly 'compacts' have the short distance to adj for full view esp sine most (all?) and variable powers.

    If you want a nice scope with plenty of forward/backward adj get a Weaver from ebay. Please dont bid against me.

  14. #14
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    The pupil of your eye is nominally 5mm. The exit pupil of the optical devise you are using should match this measurement. In other words the distance that these two measurements are equal in the eye relief.
    No.
    You are confusing exit pupil with eye relief. The exit pupil is the ratio of the Objective lens to the power of magnification. (Basically, the diameter of the beam of light)
    With binoculars, for instance, a pair of 7 X 50's will have an exit pupil of 7mm. A pair of 7 x 35's will have an exit pupil of 5mm. etc. That's why 7 x 50's are better in low light, but yet in bright sunshine they seem the same as 7 x 35. In bright light your eye pupil is about 3mm, so the advantage of bigger lenses is wasted.

    Eye relief is different. It is a distance back from the lens you can view. Longer eye relief is good for folks with glasses, for example. Eventually, you reach a point where you get the "Porthole" effect, and you're not seeing the whole field of view.

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