Skip to main content

The Advantages Of A Large Exit Pupil

The Advantages Of A Large Exit Pupil

A significant characteristic of an optical viewing instrument is the diameter of the exit pupil. The exit pupil is the circular patch of image-forming light the instrument presents to your eye. If you point a riflescope toward a brightly lighted wall or a patch of clear sky (but not at the sun!) and position your eye about 10 inches from the eyepiece, along the optical axis, you will see a bright disc of light in the center of the field. That disc is the exit pupil. The larger it is, the brighter the viewing will seem, because more of your eye will be bathed in light.

All other conditions remaining constant, changing the magnification to 6X reduces the exit pupil to 3.3mm.

You can calculate the size of a scope's exit pupil by dividing the effective objective diameter in millimeters by the magnification. For a 4X 32mm hunting scope, divide the 32mm objective size by 4 and you find that the exit pupil is a generous 8mm in diameter. With a 6.5-20X 50mm target/varmint variable scope, the exit pupil ranges from a large 7.7mm at 6.5X to a smallish 2.5mm at 20X. In a low-light situation, all other factors being equal, a lower magnification setting will provide seemingly brighter viewing than a higher one.

It is tempting to conclude that the largest obtainable exit pupil is the most desirable. But that's not always the case. The catch is that the pupil of a normal human eye opens to a maximum diameter of 5mm to 7mm, depending on the individual, even in extremely dark surroundings. Exit-pupil diameters that exceed about 7mm deliver more light than your eye can accept.

On the other hand, large exit pupils offer advantages beyond simply flooding your eye with light. With riflescopes, one of the blessings of a large exit pupil is greater freedom to position the eye with respect to the optical axis. When you must mount the rifle quickly for a now-or-never shot, you don't have the luxury of placing your eye behind the ocular with the exquisite precision a target shooter can lavish on finding the sweet spot of a 2mm or smaller exit pupil. You'll be truly grateful for the chance a large exit pupil gives you to see what you need to see, even if your eye is less than ideally located.

Looking through a 1.5-6X 20mm variable-power riflescope set to 1.5X reveals a sizeable 13.3mm exit pupil (crosshair is too out of focus to show in photo).

Another benefit of a suitably large exit pupil is the ability to see the scene clearly, without eyestrain. If you compare two scopes of equal optical quality, the one with the larger exit pupil will probably strike you as more preferable. Both will give you the same visual information, but one will make your eye work less.

Having praised generous exit pupils, I must confess that the riflescopes I use most often are fixed-power target models with exit pupils from about 1.1mm to 1.6mm. In daylight ranging from heavy overcast to bright sun they do what I need done.

Recommended


One cautionary note regarding the exit pupil. There is no correlation between the size of a scope's exit pupil and overall optical quality. Some superb scopes have small exit pupils and some real dogs have very large ones. Exit-pupil calculation is a useful tool in selecting scopes, but it isn't the whole toolbox. You should consider everything and then ultimately believe your own eyes.




GET THE NEWSLETTER Join the List and Never Miss a Thing.

Recommended Articles

Recent Videos

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Guns

Browning X-Bolt Mountain Pro

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Guns

Taurus TX 22 Competition

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Gear

Federal FireStick Precharged Loads

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Gear

Remington Core-Lokt Tipped

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Guns

Walther PDP

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Learn

Hodgdon Shooting Powder

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
News

A World Record Attempt: Practice Round and Media Day

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Learn

How to Aim with Iron Sights

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Learn

SHOOT 101: Know Your Handgun Types

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
News

Interview with Israeli Defense Forces, Part 1

The Mossberg 500 Pump Action Shotgun is one of the most popular home defense shotguns on the market. Joseph Von Benedikt...
Guns

Custom Mossberg 500 at the Range and Live Turkey!?

Shooting Times Magazine Covers Print and Tablet Versions

GET THE MAGAZINE Subscribe & Save

Digital Now Included!

SUBSCRIBE NOW

Give a Gift   |   Subscriber Services

PREVIEW THIS MONTH'S ISSUE

Buy Digital Single Issues

Magazine App Logo

Don't miss an issue.
Buy single digital issue for your phone or tablet.

Get the Shooting Times App apple store google play store

Other Magazines

See All Other Magazines

Special Interest Magazines

See All Special Interest Magazines

GET THE NEWSLETTER Join the List and Never Miss a Thing.

Get the top Shooting Times stories delivered right to your inbox.

Phone Icon

Get Digital Access.

All Shooting Times subscribers now have digital access to their magazine content. This means you have the option to read your magazine on most popular phones and tablets.

To get started, click the link below to visit mymagnow.com and learn how to access your digital magazine.

Get Digital Access

Not a Subscriber?
Subscribe Now

Enjoying What You're Reading?

Get a Full Year
of Guns & Ammo
& Digital Access.

Offer only for new subscribers.

Subscribe Now

Never Miss a Thing.

Get the Newsletter

Get the top Shooting Times stories delivered right to your inbox.

By signing up, I acknowledge that my email address is valid, and have read and accept the Terms of Use