Rifle Scopes Please Explain Eye Relief

[Cold_Bore_88]

I am not currently looking to buy another scope anytime soon. Waiting for ATACR.

However, could someone please explain eye relief to me? I realize that this may be a stupid question but a lot of the information I found online pertains to cameras and binoculars.

For example - eye relief on the 5-40X56 March is something like 98mm-100mm. On the Steiner 5-25X56 it is 90mm.

Can someone explain how this works and ultimately what it means. Is the larger number better? Why the range on the March? Is it because of the variability in the scope?

 

[orkan]

Eye relief is the distance measured between your eyeball, and the rear of the scope, to allow for a full sight picture through the scope.

Short eye relief can result in getting bopped in the eye socket by your scope during the recoil impulse. 3.5-4" is considered acceptable on most rifles. If recoil is not a concern, then shorter eye relief is also OK.

 

[HOGWILD]

Like mentioned above ! by orkan it will give you natty scope rash if it's too close!
TriggerMonkey has a great sticky that explains it as well but it is a ton of knowledge about selecting optics just not only eye relief and a great read ! http://www.snipershide.com/shooting/snipers-hide-rifle-scopes/55703-optics-selection.html

 

[Dogtown]

To add, you hear eye relief mentioned both as a distance or zone your eye needs to be behind the scope to see clearly as well as the size of that zone. Scope spec will include an actual distance measurement for eye relief such as "3.5 inches", which is fairly standard. But you'll also hear people say things like "it has good eye relief", which often applies to the size of that zone where you can see clearly. Poor quality scopes will have a very small zone so that if your eye isn't exactly 3.5" away, you start to lose the image. A good optic will have a reasonable eye relief distance and a forgiving zone where you can move your head around slightly and still keep a clear image. On a side note, sometimes you'll see "long eye relief" optics - these are intended to be used on handguns or scout rails where the shooter's eye is usually three or four times farther away than on a standard precision rifle scope.

 

[scotharr]

... But you'll also hear people say things like "it has good eye relief", which often applies to the size of that zone where you can see clearly. Poor quality scopes will have a very small zone so that if your eye isn't exactly 3.5" away, you start to lose the image. ...

Perhaps you are referring to exit pupil (for side to side movement at least)? Exit pupil can be easily calculated from the scope specs: Objective lense diameter / magnification. For example, a 25x scope with a 50mm objective has a 2mm exit pupil. Exit pupil requirements are related to your eye's pupil size. Generally, you want the exit pupil on the scope to be equal to or greater than your eye's pupil. In bright light the eye pupil is around 2.5mm and this provides a reference when selecting scopes....get at exit pupil >= 2.5mm. in low light, the pupil of a young person can be as large as 8mm and that is why "lowlight" capable scopes need a large exit pupil....to maximize light transmission to the eye. If you have a variable power scope, the easy way to increase exit pupil is turn down the magnification. The other, less convenient way is to get a larger front objective.

 

[Dogtown]

Nah, I've just noticed that when people talk about eye relief, they tend to be talking about one of two things; which is why I brought it up.

 

[Cold_Bore_88]

So ultimately, you can view the eye relief and exit pupil as a invisible cylinder behind the scope. As long as your eye is within that "cylinder", you will have a good clear picture.

I guess my "cylinder" would be the eye box.

 

[997/2man]

Eye relief is when you quit looking at photos the Shankster posts.


Massive women.

Massive.

 

[Crosshair]

One thing to consider when looking at eye relief, is that it is directly proportional to field of view (all things being equal). If you happen to notice a scope that seemingly has relatively long or short eye relief as compared to other similar offerings, you can usually see an appearant coraspondence in field of view being wider or narrower.

For instance, the 4x Acog has very short (uncomfortably so for some) eye relief but a very wide field of view for its magnification. On a 5.56 it isn't as issue, though takes some getting used to if you are used to 4" eye relief optics. Your vision from you non-scope eye is somewhat more accluded by the eyepiece being so close to your face, but the magnified image is very wide.

For hard kicking magnums, I like ateast 3.75" to over 4" just to avoid scope bite. There is a slight penalty in fov though, usually.

The design of the eye piece plays a large role with respect to eye box, field of view, and how much FOV varies with changes in magnification.

All that said, you can't glean everything about how you will like a scopes eye box, eye relief, or field of view just from comparing specs on paper, you really need to sit down behind them and compare them at all magnifications and see how your eye likes them.