Exit Pupil
Gun World|August 2017

Drinking Out Of A Fire House.

Steven K. Ledin
Exit Pupil

When drinking out of a gushing firehose, you can consume just so much. The rest spills out of your mouth and is wasted. The same principle applies when looking through an exit pupil: You can consume just so much. The rest “spills out” of your eye and is wasted.

The exit pupil of an optic is the column of light transmitted by the ocular lens, appearing as a circle of light visible in the center of the eyepiece when viewed from half an arm’s length away from your face. This exit pupil is measured in millimeters.

The formula to determine exit pupil of an optic is simple:

Objective lens diameter in millimeters divided by magnification

Example: With a 3.5-10x50 scope set at 10 power, divide the 50mm objective lens size by the magnification of 10; the answer is 5mm. Now, lower the magnification to 5x. Using the same formula, the exit pupil is now 10 (50mm objective lens divided by 5x = 10mm).

To continue the metaphor, If you can match the amount of water exiting from a firehose to the maximum amount you can drink, this is the most efficient, and nothing is wasted. You also don’t have to manhandle the impressive power that a fully charged firehose wields.

Likewise, if you can match the amount of light exiting a riflescope or binocular eyepiece to the maximum amount your eye can “swallow,” this is the most efficient, and nothing is wasted. You also don’t have to manhandle the extra weight, size and expense that an optic with a giant exit pupil might wield.

Young pupils dilate (open) a lot larger than older pupils. Various scientific studies reflect that an average maximum pupil size when dark-adjusted is about 7mm for people in their 20s to a maximum of 2mm for someone in their 80s.

Esta historia es de la edición August 2017 de Gun World.

Comience su prueba gratuita de Magzter GOLD de 7 días para acceder a miles de historias premium seleccionadas y a más de 9,000 revistas y periódicos.

Esta historia es de la edición August 2017 de Gun World.

Comience su prueba gratuita de Magzter GOLD de 7 días para acceder a miles de historias premium seleccionadas y a más de 9,000 revistas y periódicos.

MÁS HISTORIAS DE GUN WORLDVer todo
The First Rule of a Gunfight: Get a Gun
Gun World

The First Rule of a Gunfight: Get a Gun

It is a time-honored tradition within the firearms industry; a decades-old trend hobbling on, despite evidence contrary to its practices: A woman entering a gun store, walking onto a range or participating in an event inevitably hears some variation of the words, “That’s an awfully big gun for such a little lady!”

time-read
4 minutos  |
April 2017
Breaking Products And Deadlines
Gun World

Breaking Products And Deadlines

Confessions of a product test junkie

time-read
4 minutos  |
September 2017
Guns Open Doors Of Opportunity
Gun World

Guns Open Doors Of Opportunity

A Shooting Competition In Russia Emphasizes The Importance Of Freethinking And How It Opens The Door For Women Shooters.

time-read
5 minutos  |
September 2017
The Ruger 10 Mil
Gun World

The Ruger 10 Mil

Just as everyone is down-chambering 1911s to 9mm, the sr1911 goes 10mm ... For when follow-up shots aren’t an option. 

time-read
9 minutos  |
September 2017
S&W's Superb 6.5
Gun World

S&W's Superb 6.5

SMITH & WESSON’S M&P10 RIFLE GETS THE PERFORMANCE CENTER TREATMENT AND EMERGES, CHAMBERED IN 6.5 CREEDMOOR, READY TO GO THE DISTANCE.

time-read
6 minutos  |
September 2017
The Renaissance Rifle
Gun World

The Renaissance Rifle

THE HENRY BIG BOY ALL-WEATHER OFFERS UP TRUE VERSATILITY LIKE NO OTHER RIFLE.

time-read
8 minutos  |
September 2017
Ammo Of A Higher Caliber
Gun World

Ammo Of A Higher Caliber

CHOOSING THE BEST CALIBER AND BULLET TYPE FOR DEFENSIVE AMMO CAN BE A CONFUSING PROSPECT.

time-read
4 minutos  |
September 2017
Arsenal RPK - 3R
Gun World

Arsenal RPK - 3R

The Soviet/Combloc Light Machine Gun Comes To America—as A Civilian-legal Semiauto. 

time-read
7 minutos  |
August 2017
Single-Shot Hunter
Gun World

Single-Shot Hunter

Uberti has updated the old winchester 1885 high wall design into a modern carbine with old west flair.

time-read
4 minutos  |
Gunslinger Fall 2016
Best Bullet
Gun World

Best Bullet

The .44-40 WCF Is a Leading Candidate for the Best All-around Cartridge of the Old West Era.

time-read
4 minutos  |
Gunslinger Fall 2016