Eye Relief Explained: Choosing Binoculars for Comfort and Eyeglass Use

Eye relief is one of the most important comfort-related binocular specifications, yet it is often misunderstood or overlooked entirely.

If you wear glasses, use binoculars for long sessions, or find yourself experiencing eye strain, fatigue, or blackouts when viewing, eye relief is likely playing a bigger role than you realise.

This article explains what eye relief actually is, why it matters in practice, and how to interpret eye relief specs when choosing the best binoculars for yourself and comparing them to real-world use.

What Eye Relief Actually Is

Eye relief is the distance between the eyepiece lens and your eye at which the full image is visible.

In simple terms, it determines how far your eye can be from the binocular and still see the entire field of view clearly, without vignetting, shadowing, or black edges creeping into the image.

Eye relief is measured in millimetres, and while the number itself looks abstract, its effect is very tangible once you start using binoculars.

Why Eye Relief Matters in Practice

Most optics specialists would agree that there are, essentially, two different use cases in which eye relief is a major determining factor. If you wear glasses and if you are planning for long birding sessions. 

Eyeglass Wearers

For people who wear glasses, eye relief is not optional. Your glasses physically prevent your eyes from getting close to the eyepieces. 

If the binocular’s eye relief is too short, you will not be able to see the full image, even if the optics are otherwise excellent.

This typically results in:

• A reduced field of view

• Dark shadows around the edges of the image

• The feeling that the binocular is “tunnel-like”
  
  

As a general rule, eyeglass wearers should look for at least 16 mm of eye relief, and ideally closer to 17–20 mm, depending on the thickness of their lenses and frames. 

We have put together a very helpful guide on choosing binoculars if you wear eyeglasses that we encourage you to check out before making a purchase. 

Long Viewing Sessions

Even if you do not wear glasses, eye relief plays a major role in comfort over time.

Short eye relief forces you to hold your eyes very close to the eyecups and maintain a precise position. Over extended viewing sessions, this can lead to eye strain, facial pressure, and general discomfort.

I know I’ve been so consumed in a particularly good birding day that hours go by in a flash and, before I know it, my eyes are hurting and I’ve got big sensitive rings around them. 

These are often common when you’re somewhere like Latin America, where the birding action can be absolutely non-stop, particularly if it’s your first time in a place like Costa Rica or Colombia (or really anywhere new) and you are checking off lifers left, right and centre. 

I could easily spend a whole day looking at an emerald toucanet. 

Adequate eye relief gives you a little positional tolerance. You do not need to “lock” your eyes into one exact spot to maintain a clean image, which makes long observation sessions more relaxed and forgiving.

Recommended Eye Relief Ranges

While there is no single perfect number for everyone, the following ranges are useful as general guidance:

• Under 14 mm
  Often restrictive, especially for eyeglass wearers. Can feel fatiguing during long use.

• 14–16 mm
  Usable for many people without glasses, but borderline for eyeglass wearers.

• 16–18 mm
  A comfortable range for most users, including many eyeglass wearers.

• 18 mm and above
  Excellent for eyeglass wearers and extended viewing sessions, offering maximum comfort and flexibility.
  
  

It is important to remember that eye relief is not a quality rating. Shorter eye relief does not mean worse optics. It simply reflects a different design trade-off.

How Twist-Up Eyecups Interact with Eye Relief

Eye relief and eyecups work together.

Twist-up eyecups allow you to adjust the distance between your eyes and the eyepiece so that you can position your eyes at the correct eye relief point.

• If you wear glasses, eyecups should be fully retracted so your eyes sit closer to the lenses.

• If you do not wear glasses, extending the eyecups helps place your eyes at the optimal viewing distance.

Good eyecups do not increase eye relief, but they help you use the available eye relief correctly. Poorly designed eyecups can make even generous eye relief feel awkward or imprecise.

Common Misconceptions About Eye Relief

One common misconception is that eye relief only matters if you wear glasses. In reality, it affects everyone’s comfort, especially during long sessions.

Another is that more eye relief is always better. Extremely long eye relief can sometimes make eye placement more sensitive, particularly if eyecups lack firm stop positions. Balance matters more than extremes.

~14–15 mm Eye Relief

Typical feel: Acceptable for shorter sessions, more sensitive eye placement

Comfort for extended use: Comfortable for short to moderate viewing sessions, but may feel a little restrictive over long periods.

Suitable if you wear glasses: Marginal. Many eyeglass wearers will struggle to see the full field of view, especially with thicker lenses.

Best suited for: Users without glasses who prioritise compact size or higher magnification and tend to observe in shorter bursts.

~16–17 mm Eye Relief

Typical feel: Balanced and forgiving

Comfort for extended use: Comfortable for most users, even during longer viewing sessions, with less eye strain and fewer positioning issues.

Suitable if you wear glasses:  Yes, for many eyeglass wearers. Most users will be able to see the full image with eyecups fully retracted.

Best suited for:  General birding, wildlife watching, mixed use, and users who may or may not wear glasses.

~18 mm+ Eye Relief

Typical feel: Relaxed and highly comfortable

Comfort for extended use:  Excellent. Allows a relaxed viewing position with minimal eye strain during prolonged observation.

Suitable if you wear glasses:  Yes. Well suited to eyeglass wearers, including those with thicker frames or lenses.

Best suited for:  Eyeglass wearers, long viewing sessions, premium all-round binocular use where comfort is a priority.

NatureRAY Eye Relief in Practice

Below I’d like to run through some of the eye relief specs on our NatureRay line so that you have a better idea of what kind of eye reliefs are readily available when shopping for or trying out binoculars. 

NatureRAY Outrek 10x42

Eye relief: 15 mm

With 15 mm of eye relief, the Outrek 10x42 offers acceptable comfort for general use, particularly for users who do not wear glasses.

For eyeglass wearers, this eye relief is on the shorter side. Some users may not be able to see the full field of view comfortably, especially if their glasses have thicker lenses or frames.

Comfort for extended use:  Good for short to moderate sessions

Suitable if you wear glasses:  Almost certainly not. May work for some users, but not guaranteed

NatureRAY Outrek 8x42

Eye relief: 18 mm

An eye relief of 18 mm makes the Outrek 8x42 noticeably more comfortable, particularly during longer viewing sessions.

This is a forgiving eye relief range that allows relaxed eye placement and works well for most eyeglass wearers when the eyecups are fully retracted.

Comfort for extended use: Very good. Suitable for prolonged observation

Suitable if you wear glasses:  Yes, for most users

NatureRAY Outrek 8x32

Eye relief: 18 mm

Despite its compact size, the Outrek 8x32 provides generous eye relief, making it comfortable to use for extended periods.

The combination of low weight and longer eye relief makes this model easy on the eyes during active birding or travel use.

Comfort for extended use:
Very good, especially given its lightweight design

Suitable if you wear glasses:
Yes

NatureRAY Trailbird 10x42

Eye relief: 14.3 mm

The Trailbird 10x42 has relatively short eye relief, which reflects the trade-offs involved in compact 10x designs.

For users without glasses, it is perfectly usable. For eyeglass wearers, seeing the full field of view may be difficult or inconsistent.

Comfort for extended use:  Acceptable for shorter sessions

Suitable if you wear glasses:  Generally no, or only with very thin lenses

NatureRAY Trailbird 8x42

Eye relief: 17.8 mm

At 17.8 mm, the Trailbird 8x42 offers a comfortable and forgiving viewing experience.

This eye relief supports long sessions and works well for most eyeglass wearers without feeling overly sensitive to eye position.

Comfort for extended use: Excellent

Suitable if you wear glasses:  Yes, for most users

NatureRAY Trailbird 8x32

Eye relief: 17.8 mm

The Trailbird 8x32 combines compact dimensions with generous eye relief, making it a strong option for users who want portability without sacrificing comfort.

This eye relief range allows relaxed viewing and good compatibility with glasses.

Comfort for extended use:  Excellent for a compact binocular

Suitable if you wear glasses:  Yes

NatureRAY Trailbird 10x50

Eye relief: 17.8 mm

Despite its higher magnification and larger objective lenses, the Trailbird 10x50 maintains a comfortable eye relief.

This helps offset the more demanding nature of 10x viewing and contributes to a more relaxed experience during longer sessions.

Comfort for extended use:  Very good

Suitable if you wear glasses:  Yes, for most users

NatureRAY Scenic Pro ED 10x42

Eye relief: 16.7 mm

The Scenic Pro ED 10x42 sits in a balanced eye relief range that works well for both comfort and control.

Most eyeglass wearers will be able to see the full image, and the binocular remains comfortable during extended use without being overly sensitive to eye placement.

Comfort for extended use:  Very good

Suitable if you wear glasses: Yes, for most users

NatureRAY Scenic Pro ED 8x42

Eye relief: 18.4 mm

With 18.4 mm of eye relief, the Scenic Pro ED 8x42 offers excellent comfort and flexibility.

This is an ideal specification for eyeglass wearers and users who spend long periods behind the binoculars, providing a relaxed and forgiving viewing experience.

Comfort for extended use:  Excellent

Suitable if you wear glasses: Yes, including users with thicker lenses

Putting It All Together

Eye relief is best thought of as a comfort specification, not a performance one.

If you wear glasses it determines whether you can see the full image at all.
If you observe for long periods, it influences how relaxed and fatigue-free the experience feels.

When choosing binoculars, eye relief helps answer two very practical questions:

• Will this be comfortable to use for extended periods?

• Will this work properly if I wear glasses?

Understanding eye relief allows you to answer those questions before you ever put binoculars to your eyes.