When it comes to riflescopes and optics, having the proper eye relief is crucial for a clear, comfortable viewing experience and safe shooting. But what is eye relief on a scope? Eye relief refers to the maximum distance from the rear lens or ocular at which you can still see the full circular field of view. Getting this optimal eye positioning allows you to take full advantage of the scope’s light transmission and wide picture without straining your eyes or risking injury from recoil. In this guide, we’ll explore eye relief in-depth – what it is, why it matters, how to measure it, and what eye relief specifications are ideal for different shooting applications.
What is Eye Relief?
Eye relief is the maximum distance from the rear lens or ocular lens of a scope or optic at which the viewer can see the entire field of view. It is essentially the eye relief or eye box – the exit pupil area where your eye needs to be positioned to take full advantage of the scope’s light transmission and see the entire circular image clearly. Having sufficient eye relief allows you to get a full sight picture without having to press your eye uncomfortably close to the eyepiece. The eye relief measurement is the distance from the surface of the outer lens to the exit pupil where you get the optimum viewing position. If your eye goes beyond this distance, you’ll start to see a dark vignette around the edges of the sight picture. Getting the proper eye relief helps prevent this as well as eyestrain and recoil issues when shooting.
Why is Eye Relief Important for Scopes?
Proper Eye Positioning
Having adequate eye relief allows the shooter to position their eye at an optimal distance from the eyepiece to see the full field of view. If the eye relief is too short, the shooter has to press their eye uncomfortably close to the scope to get a full sight picture.
Recoil Protection
Adequate eye relief helps protect the shooter’s eye from recoil, especially when shooting larger caliber rifles or magnum loads. Without enough eye relief, the scope can make contact with the shooter’s eye socket or brow upon firing, resulting in painful scope eye injuries.
Full Field of View
Ensuring the eye is within the eye relief zone allows the shooter to take full advantage of the scope’s light transmission and see the entire circular field of view without any dark vignetting around the edges.
Eye Box Flexibility
Scopes with longer eye relief provide a more forgiving eye box or exit pupil positioning, making it easier to acquire the full sight picture, especially for shooters who wear glasses or shooting from awkward positions.
Reduced Eyestrain
Proper eye relief prevents the need to strain and press one’s eye up against the eyepiece uncomfortably, reducing fatigue over long shooting sessions.
By providing the optimal eye positioning and exit pupil distance, adequate eye relief enhances shooting accuracy, safety, and comfort when using riflescopes and other optics.
How Do You Measure Eye Relief?
The eye relief of a scope is typically measured from the outermost surface of the outer lens or ocular lens to the exit pupil – the point where you can see the full circular field of view.
To measure eye relief:
- Set up the scope on a stable platform or shooting rest aimed at a plain backdrop like a wall or blank target.
- Look through the scope and position your eye at the point where the entire circular field of view is visible without any dark vignetting around the edges. This is the exit pupil position.
- Using a ruler, measure the straight-line distance in millimeters or inches from the outer lens surface to your eye’s position at the exit pupil.
- This measured distance is the eye relief specification for that particular scope and magnification setting.
Some key points:
- Eye relief should be measured with the scope focused at infinity.
- Eye relief may change slightly at different magnification levels on variable scopes.
- Use a consistent eye position and head positioning when measuring.
- Mark or note the eye relief value for future reference.
Manufacturers also measure and specify the eye relief as part of the scope’s technical specifications. But checking it yourself ensures getting the proper fit and eye positioning for your specific use case.
What Factors Affect Eye Relief?
Objective Lens Size
Larger objective lenses generally require longer eye relief to provide enough room between the ocular lens and the exit pupil. Smaller objectives can have shorter eye relief.
Magnification Level
Higher magnification settings tend to decrease eye relief compared to lower magnification on variable scopes. The eye relief may change slightly through the magnification range.
Lens Design
The specific lens design, including the number of lens elements and their configuration, impacts how much physical space is needed between the ocular lens and exit pupil.
Eye Box Constraints
Some scopes are designed with tighter eye box specifications which can limit the eye relief distance while still allowing the full field of view.
Reticle Plane
Whether the reticle is located in the front or rear focal plane can slightly influence the position of the exit pupil and eye relief measurement.
Parallax Settings
Adjusting the parallax on scopes that have this feature may cause minor changes in the eye relief position.
Eyepiece Design
Eyepieces designed with larger ocular lenses or different eye relief lens elements can extend or shorten the eye relief distance.
How Does Eye Relief Impact Scope Performance?
Field of View
Having sufficient eye relief allows the shooter to properly position their eye to see the full circular field of view that the scope is designed to provide. If eye relief is too short, the viewer will experience dark vignetting around the edges, reducing the effective field of view.
Eye Box
Scopes with longer eye relief tend to have a more forgiving and larger eye box or exit pupil area where the eye can be positioned. This makes it easier to quickly acquire the full sight picture, especially from non-ideal shooting positions or for those wearing glasses.
Light Transmission
Being properly positioned within the eye relief zone allows maximum light transmission through the scope’s lens system to reach the viewer’s eye for a bright, high-contrast image.
Recoil Protection
Adequate eye relief is critical for preventing scope eye injuries from recoil, especially on larger caliber rifles and magnum loads. Not having enough distance can result in the scope impacting the shooter’s eye socket or brow.
Eyestrain/Fatigue
Proper eye positioning within the eye relief prevents having to strain and press one’s eye uncomfortably close to the eyepiece. This reduces eyestrain and fatigue over extended shooting sessions.
Shooting Accuracy
By providing the optimal exit pupil positioning, sufficient eye relief helps ensure a clear, full sight picture for improved accuracy and shot placement when shooting at longer ranges or smaller targets.
What Eye Relief is Best for Different Applications?
Long-Range Precision Shooting
For long-range precision and target shooting with high-magnification scopes (>10x), a longer eye relief in the 3.5-4 inch (90-100mm) range is preferred. This allows enough distance for proper eye positioning and recoil protection when shooting from various positions.
Hunting Scopes
For typical hunting rifle scopes in the 3-9x or 4-12x magnification ranges, an eye relief of 3-3.8 inches (75-95mm) is commonly used. This provides a good balance of eye box size and recoil clearance for most hunting calibers.
Dangerous Game/Magnum Calibers
When hunting dangerous game or using hard-kicking magnum cartridges, an extremely long eye relief of 4+ inches (100mm+) may be necessary to keep a safe distance and avoid scope eye injuries from heavy recoil.
Tactical/AR Optics
For close/medium range tactical red dot sights and low-power variable optics on AR-platform rifles, a shorter 2.5-3.5 inch (65-90mm) eye relief works well while allowing a more compact scope setup.
Rimfire/Air Rifle Scopes
Due to negligible recoil, rimfire and air rifle scopes can utilize very short eye reliefs around 2-3 inches (50-75mm) to keep the scope’s length and weight down.
Scout Scopes
The eye relief on dedicated scout-style forward-mounted rifle scopes is typically in the 3-4 inch (75-100mm) range to accommodate the non-traditional mounting position.
Can Eye Relief Be Adjusted on a Scope?
Yes, eye relief can be adjusted on certain types of scopes, but the adjustability depends on the specific scope design.
Fixed Parallax Scopes
On basic fixed parallax rifle scopes, the eye relief distance is a fixed value determined by the scope’s optical design. There is no adjustment possible – the exit pupil position is set.
Adjustable Objective (AO) Scopes
Many higher-end scopes feature an adjustable objective lens housing that can rotate. Turning the adjustment ring moves the objective lens element position relative to the ocular lens. This effectively changes the eye relief distance.
Side Parallax Adjustment
Some scopes have a side parallax adjustment knob calibrated for different distances. Adjusting this compensates for parallax error, but also shifts the exit pupil position, slightly altering the eye relief.
Removable Eyepieces
A few specialty scopes, like the Nightforce NXS models, allow replacing the eyepiece module itself. Different eyepiece options provide varied eye relief distances to optimize the scope for the shooter’s needs.
Eye Relief Extenders
Aftermarket eye relief extender devices can be inserted into the rear scope housing to increase the eye relief by creating more distance between the shooter’s eye and the ocular lens.
When eye relief is adjustable, the shooter can tailor the exit pupil positioning for:
- Using with or without glasses/optics
- Avoiding interference with facial features or shooting positions
- Optimizing eye box for quick target acquisition
- Mitigating recoil based on the firearm’s caliber/load
Having the ability to fine-tune eye relief customizes the scope’s optical performance for the individual user’s needs.
What Are Some Common Eye Relief Issues and Solutions?
Insufficient Eye Relief
Issue: Not having enough eye relief distance causes the shooter to press their eye uncomfortably close to the eyepiece or experience vignetting around the edges of the sight picture.
Solutions:
- Choose a scope model with a longer eye relief specification
- Use adjustable objective or parallax controls to increase eye relief if available
- Add an eye relief extender device to the rear of the scope
- Switch to lower magnification settings which can increase eye relief slightly
Recoil Contact Issues
Issue: With heavy recoiling firearms, the scope can violently make contact with the shooter’s eye socket or brow due to inadequate eye relief, potentially causing injury.
Solutions:
- Use a scope specifically designed for long eye relief (4″+ or 100mm+) for dangerous game/magnum rifles
- Adjust for maximum eye relief distance using available controls
- Consider mounting the scope farther forward on the rifle
Eye Box Limitations
Issue: Difficulty quickly acquiring a full sight picture due to an unforgiving eye box/exit pupil positioning.
Solutions:
- Choose a scope model with longer advertised eye relief for a larger eye box
- Adjust eye relief using available controls for an optimal position
- Mount the scope at a different height or eye relief to match your shooting position
Interference with Glasses/Accessories
Issue: Inadequate eye relief causes vignetting or makes it difficult to use the scope while wearing glasses or using other optical accessories.
Solutions:
- Maximize the eye relief distance with available adjustments
- Try mounting the scope slightly higher or lower to avoid interference
- Use eye relief extender devices if scope allows
- Consider scopes specifically designed for longer eye relief usage with glasses
By being aware of potential eye relief limitations and using available solutions, shooters can optimize their scopes for a clear, comfortable viewing experience tailored to their individual needs.
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