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Aberration - Aberrations are imperfections inherent to all
optics designs. The best optics limit aberration as much as
possible to provide a clear, accurate image. One example
of aberration is chromatic aberration, which occurs when
lenses in an optic incorrectly refract different colors of light.
The result of this aberration is differing focal points and a
distorted image.
Adjustable Objective - An Adjustable Objective (AO) is
a dial around the objective end of the scope or a knob on
the left side of the turret housing. It allows you to adjust
your scope’s parallax to a certain distance by moving
these adjustments until a clear picture is perceived and/
or the marked corresponding incremental yardages are
approximated to your target distance.
Concerning parallax, an adjustable objective is typically a
dial of sorts located either at the objective end of the scope
or a dial on the left side of the turret (commonly called
Side AO). Most AO set-ups are designated in yards, and by
adjusting the AO to the approximate distance to the target,
resolving the potential parallax.
Ballistic Reticle - A ballistic reticle is a reticle that includes
various factors to ensure the correct aiming point. They are
used to increase the range of an aimed shot and predict
the bullet’s flight at an angle. Ballistic reticles use BDC
technology to correlate angles, atmospheric conditions,
ammunition data, and angles. Ballistic reticles come in
different flavors, with different designs, densities, and
different stage lines and crosshair heights.
Ballistic Turret - A ballistic turret is a feature common
to expensive and high-end riflescopes. It allows you to
set several preset distances. It helps to eliminate the
uncertainty in the distance estimation and eliminates the
need for ballistic reticles.
Bullet Drop Compensation - BDC The principle of
interaction between the fired bullet, gravity, and target
indicators.
Centerfire - Centerfire is a concept relevant to all cartridges,
including shot, hand, and rifle weapons. Indicates the point
at which the weapon striker hits the bullet base becomes
the catalyst that triggers the chain of events that lead to the
shot.
Coatings - Microscopic coatings on the lens surfaces reduce
light loss and glare due to reflection. Coated lenses offer a
brighter, higher-contrast image with less eyestrain. More
coatings allow better light transmission, but it is possible to
have a scope with a single coating to outperform a scope
with multicoated lenses greatly. It all depends on the quality
of the coatings and the glass. Good quality does not come
cheap. The following are acceptable terms for coatings:
• Coated: A single layer on at least one lens surface.
• Fully Coated: A single layer on all air to glass surfaces.
• Multicoated: Multiple layers on at least one lens surface.
• Fully Multicoated: Multiple layers on all air to glass surfaces.
Click - A click is one adjustment notch on the windage or
elevation turret of a scope. One-click most often changes a
scope’s point of impact 1/4 inch at 100 yards. Some clicks
are 1/8 inch, 1/2 inch, one inch, or even more.
Duplex Reticle - A duplex reticle is available in the most
common reticle style, with many conventional, affordable,
and entry-level rifle scopes. It typically features a reticle with
crosshairs reaching the entire edges of the field of view.
As the crosshairs reach to meet like a “t” or a cross in the
center, the posts’ thickness may or may not become finer.
Each duplex-style reticle can vary slightly from one optics
brand to another.
Exit Pupil - An exit pupil is the small circle (column) of
light visible in the ocular lens when you hold your scope
(or binocular) at arm’s length. The larger the exit pupil is,
the brighter the image entering your eye. To find the exit
pupil for your scope, divide the objective lens diameter
in millimeters by the magnification. For example, if your
scope is four power (4X), and your objective lens is thirty-
six millimeters in diameter (36mm), divide four into 36, and
it equals 9. Therefore, nine would be the exit pupil size in
diameter in millimeters. Typically measured in millimeters,
the larger the size of the exit pupil, the brighter the scope
image will be.
Eye Relief - Eye relief is the distance your eye must be
from the ocular lens and still get a full field of view. This
measurement is usually defined in inches.
Fast Focus Eyepiece - The Fast Focus Eyepiece is a
European-style eyepiece technology with a fraction of a turn
focal length. It allows you to focus on the grid, which gives
you a sharp and clear image. At the same time, the focusing
speed is higher than the standard method. Frequently,
however, the Fast Focus Eyepiece does not have a locking
mechanism for the slower method.
First Focal Plane - FFP is an indication of the first (focal)
plane to the position of the reticle. FFP scopes retain the
amount of stretch, while the size of the crosshair of the sight
will correlate with the image’s magnification.
Field of View - Field of view (FOV) is the amount of
area seen through your scope from right to left at 100
yards. As magnification is increased, FOV is lessened. As
magnification is decreased, FOV is increased.
Fixed Power - denotes a fixed magnification of the sight. It
does not have a range of power settings from low to high,
as the manufacturer sets a constant increase within a certain
scaling.
Hold Over/Under - Holdover/under is the amount of point
of aim change either above or below your target, without
adjusting your scope, to adjust for the trajectory of your
projectile.
GLOSSARY OF COMMON RIFLESCOPE TERMS