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  • Post last modified:October 27, 2023

What exactly is an eye box when using a magnified optic?

The eye box is the area behind the optic to freely move the position of the eye closer, further, up/down, left/right, and still see a clear field of view on a given scope magnification setting and eye relief distance.

Rifle scope eye box illustration

In other words, the eye box is the sweet spot where those threshold amounts overlap without being shadowed.

Here is how it works:

How Does It Work

1X Reflex Sights

eotech exps3 pov 1

Red dot sight has unlimited eye relief, free parallax, and allows flexible head movement behind the optic and still acquires the reticle.

fn509 trijicon sro pov in action

The eye box for a red dot sight is very forgiving.

This means:

  • Very flexible optic to eye distance requirement
  • Very flexible head movement as long the the optic's field of view is large
  • Aim with both eyes open
  • Can be used on pistol 
  • Doesn't have to center the eye behind the optic

Fixed Magnification Optics

ELCAN dual role weapon sight scope shadow

Fix magnification optics have eye relief threshold and exit pupil limitations.

The sweet spot behind the optic is when the shooter doesn't see scope shadow regardless of what the magnification power is.

Rule of thumb: 4" eye relief is common

This means:

  • Shooter must find the sweet spot behind the optic and be consistent with it
  • Scope shadow appears when getting too close or too far from the ocular lens

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Variable Magnification Optics

The eye box of a variable magnification scope works the same as a fixed magnification optic.

vortex razor HD scope turrets

When the magnification changes, the eye box will change.

This means:

  • Eye relief distance shortens as magnification power increases
  • Scope shadow is much more sensitive if the eye isn't center behind the optic
  • Restricts head movement when exit pupil and eye relief are tight
  • Larger the exit pupil the more forgiving the eye relief is
  • Magnification increases as less light passes through the scope to the shooter's eye

Why Does It Matter?

Eye box limitation when using an optic affects the following:

  • Shooting position
  • Optic height
  • Optic mounting locations
  • Which optic to buy or time to swap

Improvised Shooting Positions

When aiming through the optic in improvised shooting positions, a large field of view red dot sight is the best for maximizing head movement behind the optic and situational awareness.

It allows the shooter to place the reticle on targets while:

  • Leaning left / right
  • Prone
  • Angled
  • Behind covers
  • Through holes
  • In tight spaces
  • Many more...

It's much harder to do this with a magnified optic.

Optic Mounting Locations

Every shooter should find the sweet spot on the rifle to mount an optic, to have a consistent cheek weld position, and ideal eye to optic distance to acquire the sight.

Mounting a red dot sight close to the eye maximizes the field of view and gives much more flexible head movement for CQB applications.

Mounting a magnified optic requires personally fitting. Once it's comfortable for you, then start the zeroing process.

Minot AFB security forces M4 with ACOG 4X scope

Sometimes a short eye relief scope can lead to scope eye bite on high recoil rifles, or bump into shooter's helmet. 

Optic Height

Check the optic mount height if the cheek weld position is too low or too high. This is where buying an optic mount with different heights comes into play.

Buy New Optics

The best way to check out these optics is in your local stores and see for yourself in person. If you already know what you want to buy, please check out some great deals here.