Optics Terms Defined: Aberrations

The purpose of an optic is to deliver a true-to-life image. Sometimes that goes a bit sideways (or spherical) ...

by
posted on February 29, 2024
** When you buy products through the links on our site, we may earn a commission that supports NRA's mission to protect, preserve and defend the Second Amendment. **
spherical-aberration-disk.jpg

Any difference between the image of an object viewed through a riflescope and the ideal image of that object is called "aberration." Here are some of the more common types of aberration that you might hear about when optics are being discussed.

Chromatic aberration
This is a color flare or color fringe along the edges of objects in the image.

Spherical aberration
This occurs when light rays passing through the center of the lens do not focus at the same point as rays of light passing through the lens edges. The result is a low-contrast, soft-focus image.

Pincushion and barrel distortion
This is the tendency of straight lines to "bow in" or "bow out" from the center of the image to its edges.

Astigmatism
This is the inability to focus the image due to imperfections in the lens system.

Curvature of field
The image is not flat. Straight lines appear to be bent.

It is important to recognize that no optical system can be completely free of aberration. All optical systems are a design compromise that minimizes some types of aberration while necessarily allowing others. Many of the lens elements in a riflescope are included for the purpose of correcting various types of aberration.

Aberration is not simply the result of imperfect lens grinding or improper design; some types of aberration are basically inevitable, due to the fact that different wavelengths of light focus at different points. Also, some types of aberration result from the characteristics of spherical lenses (lenses whose curved surfaces are ground with an equal-radius curvature). Some forms of aberration can be eliminated by the use of aspherical lenses.

More like this from around the NRA

Latest

Savage Proof Testing Lede
Savage Proof Testing Lede

What Is "Proof Testing"? Savage Arms Demonstrates

When a company tells you their firearms have been "proof tested," here's what they mean ... and how it's done!

What the "21-Foot Rule" Means for Self-Defense

In a defensive situation, things can happen very quickly. How fast? This fast.

NRA Family Columnist Serena Juchnowski Partners with SIGHTRON

Competitive shooter and outdoor writer Juchnowski won our writing contest 11 years ago, and she's just getting started.

Video Review: Kimber KDS9c

Many double-stack 1911-style pistols are a bit hard to conceal ... but not this one!

3 CCW Ideas for Active Lifestyles

Hiking, biking and horseback riding ... with the right concealed-carry setup, safety and comfort go hand-in-hand.

First Impressions: Smith & Wesson M&P15 AXE Rifle Series

Created for suppressed shooting, these four 5.56 NATO rifles look sharp and shoot with scalpel precision.

Interests



Get the best of NRA Family delivered to your inbox.