Weapons & Marksmanship Fundamentals Core

Optics Basics: Scopes, Binoculars & Rangefinders

Lesson 28 of 60 · Module 4, lesson 7

Your objective

By the end, you'll be able to interpret a scope's and binocular's specs, explain eye relief, reticle, and MOA/MIL, and choose magnification to match your hunting.

Concept ~9 min

You pick up two scopes. One says “3-9x40,” the other “4-16x50,” and the second one costs three times as much. Bigger numbers, better scope, right? Not necessarily — and buying the wrong glass for your woods can cost you the deer of the season. Learn to read the numbers and you’ll choose like you know what you’re doing, because you will.

Quick recall

Quick recall from Ballistics Fundamentals — what does your scope's adjustment let you set so point of aim equals point of impact?

The zero — the distance where aim and impact match The caliber of the rifle

Show answer

Correct: The zero — the distance where aim and impact match — Right. The turrets move the reticle to set your zero. The units they move in (MOA or MIL) are a big part of this lesson.
Not quite: The caliber of the rifle — Caliber is fixed by the rifle. The scope sets your zero — the aim-equals-impact distance — by moving the reticle.

Reading a riflescope’s numbers

Every scope’s name is a spec sheet. Take 3-9x40:

3-9x is the magnification — here, variable from 3x to 9x. At 3x the target looks 3 times closer; at 9x, 9 times. A fixed scope (like 4x) has one setting (Vortex, Magnification & Field of View).
40 is the objective lens diameter in millimeters — the front lens that gathers light. A bigger objective is brighter but heavier and sits higher on the rifle (Leupold Glossary).

Two trade-offs ride along. Field of view (how much you see) shrinks as magnification climbs — crank to 9x and a moving deer is harder to find (Vortex). And exit pupil — objective ÷ magnification — drives low-light brightness: a 40mm at 8x gives a 5mm exit pupil, about what a dark-adapted eye uses. Lowering power widens the exit pupil and brightens the image (Vortex, low-light performance).

Explore

Tap each part of the scope spec to see what it means.

Diagram of a riflescope with a large front objective lens on the left, an eyepiece on the right, and an adjustment turret on top. Below it reads 3-9 x 40.

Eye relief and the reticle

Eye relief is the distance from your eye to the rear lens where you see a full, edge-to-edge image (Leupold Glossary). You set it when you mount the scope — slide it fore and aft until you get a full picture in a natural shooting position, no closer than about 3/8 inch from the magnification ring (Vortex, Mounting a Riflescope). Get this wrong on a hard-recoiling rifle and the scope kicks back into your eyebrow — “scope bite.”

The reticle is the aiming mark inside the scope. The classic is a duplex — thick outer posts that draw your eye to a fine center crosshair. A BDC (bullet-drop compensating) reticle adds hash marks below center to hold over for longer ranges (Leupold Glossary).

MOA and MIL — the units of adjustment

Turrets move the reticle in tiny angular steps, not inches, because an angle covers more inches the farther out you go. Two systems:

MOA (minute of angle) is 1/60th of a degree. It spreads about 1 inch per 100 yards (1.047 inches, to be exact) — so 1 MOA is ~2 inches at 200, ~3 at 300. Most scopes click in 1/4 MOA (NSSF, Minute of Angle).
MIL (milliradian) is 1/1000th of the distance: 3.6 inches at 100 yards, 10 cm at 100 meters. One MIL equals about 3.44 MOA, and most MIL turrets click in 0.1 MIL (NSSF, Milliradians).

Neither is “better” — pick a scope whose turret and reticle speak the same language so your holds and clicks match.

Diagram showing that one MOA covers about one inch at 100 yards, two inches at 200 yards, and three inches at 300 yards — the same angle covers more inches the farther out you go. — Diagram (not to scale). One MOA is an angle, so it covers more inches the farther away the target is: ~1 inch at 100, ~2 at 200, ~3 at 300 yards.

Edge case First vs. second focal plane (why a holdover reticle can lie)

In a first focal plane (FFP) scope the reticle grows and shrinks with magnification, so its hash-mark spacing (subtension) is correct at any power. In a second focal plane (SFP) scope the reticle stays one size, so its holdover marks are only accurate at one magnification — usually the highest (Leupold Glossary). If you use a BDC/MIL reticle to hold over, know which kind you have and at what power it’s true.

Binoculars, and choosing for your hunt

Binoculars read the same way: 8x42 is 8x magnification, 42mm objective. For hunting, the big choice is 8x vs 10x: 8x gives a wider field of view and is easier to hold steady — better in thick cover; 10x reaches farther for open country but is shakier and shows less (Maven, choosing hunting binoculars).

The same logic picks your scope. Match magnification to your hunting: in the Piedmont’s thick woods and close shots, a low-power scope (something like 1–6x or 2–7x) finds and follows deer faster; for open fields and longer pokes, more top-end power helps. And remember glass quality and coatings beat a giant objective — a good optic with a smaller objective outperforms a cheap one with a big bell (Vortex).

Pick the right glass

Decision

You'll hunt thick Piedmont hardwoods where most shots are inside 100 yards, often in low light at dawn and dusk. A salesman pushes a 6-24x50 'tactical' scope. Good fit?

Yes — more magnification is always an advantage

At 6x minimum, your field of view is tight and finding a close, moving deer in the brush is slow. That much top-end power is wasted in the woods. Wrong tool.

No — pick a lower-power scope (like 2-7x or 3-9x) that finds close deer fast

Right. A wide, low-power field of view acquires close deer quickly. You don't need 24x for 80-yard timber shots. Match the glass to the woods.

Check the numbers

Knowledge check

A scope is marked 4-12x44. What does the '44' tell you?

The objective lens is 44mm — the light-gathering front lens It magnifies up to 44 times It adjusts in 44 MOA clicks

Show answer

Correct: The objective lens is 44mm — the light-gathering front lens — Right. The number after the x is the objective diameter in millimeters. 4-12x is the magnification range.
Not quite: It magnifies up to 44 times — No — 4-12x is the magnification (4x to 12x). The 44 is the objective lens diameter in millimeters.
Not quite: It adjusts in 44 MOA clicks — No. The 44 is the objective diameter in mm. MOA/MIL is the turret's click value, a separate spec.

Knowledge check

One MOA is roughly how big at 300 yards?

About 3 inches About 1 inch About 10 inches

Show answer

Correct: About 3 inches — Right. MOA is an angle ~1 inch per 100 yards, so ~3 inches at 300. The same angle covers more inches farther out.
Not quite: About 1 inch — That's 1 MOA at 100 yards. Because it's an angle, it grows to ~3 inches at 300 yards.
Not quite: About 10 inches — That's closer to 1 MIL at ~280 yards. 1 MOA is ~1 inch per 100 yards, so ~3 inches at 300.

Take it to the woods

Choose and set up your glass

0/5

I matched my scope's magnification range to how I actually hunt (lower power for thick woods, more top-end for open country).
I can read any scope or binocular spec out loud and say what the magnification and objective mean.
Safety I set eye relief so I get a full image in my natural shooting position and the scope can't reach my eyebrow. Scope bite on a recoiling rifle is a real injury.
I know whether my turret/reticle is MOA or MIL — and that they match each other.
I leveled the reticle and torqued the rings evenly before zeroing.

Sources

Vortex Optics, Understanding Magnification & Field of View — https://vortexoptics.com/blog/understanding-magnification-and-field-of-view.html
Vortex Optics, What Makes Great Low-Light Performance (exit pupil, glass/coatings) — https://vortexoptics.com/blog/what-makes-great-low-light-performance.html
Vortex Optics, How to Properly Mount a Riflescope (eye relief, leveling, torque) — https://vortexoptics.com/blog/how-to-properly-mount-a-riflescope.html
Leupold Optics Glossary (eye relief, reticle, MOA/MIL, focal plane) — https://www.leupold.com/glossary
NSSF, Minute of Angle (MOA) Explained — https://www.nssf.org/shooting/minute-angle-moa/
NSSF (Let’s Go Shooting), What Are Mils (Milliradians)? — https://www.letsgoshooting.org/resources/articles/rifle/what-are-mils-milliradians/
Maven, How to Choose Binoculars for Hunting — https://mavenbuilt.com/blogs/blog/how-to-choose-binoculars-for-hunting-hunting-binocular-guide

If you remember nothing else

A scope marked 3-9x40 means 3x to 9x variable magnification with a 40mm objective lens; the objective gathers light, so bigger is brighter but heavier.
Eye relief is how far your eye sits from the scope for a full image — set it right when mounting so recoil never drives the scope into your eyebrow.
The reticle is your aiming mark. MOA and MIL are both angular units for adjustments and holdover: 1 MOA is about 1 inch at 100 yards; 1 MIL is 3.6 inches at 100 yards.
Exit pupil (objective ÷ magnification) drives low-light brightness, but glass quality and coatings matter more than a big objective.
Match magnification to your hunting: lower power for thick woods and close shots, higher power for open country — and don't over-magnify.

How ready do you feel?

How ready are you to walk into a shop, read the numbers on a scope or binocular, and pick the right magnification for where you hunt?

Before you go — a quick look back

Distributed practice: one fast recall from an earlier lesson keeps it from fading.

Quick recall

From Ballistics Fundamentals — what is the 'zero' that a scope's adjustments are used to set?

Show me the answer

Show answer

Correct: Show me the answer — The distance at which your point of aim equals your point of impact. The scope's turrets move the reticle in angular units (MOA or MIL) to put the bullet's arc on your aim point at that distance — which is exactly why those units exist.

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