Lens aberrations explained - phillipreeve.net

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Introduction

In many of our lens reviews we talk about certain kinds of aberrations, so this article shall give you an overview of typical lens aberrations, tell you in what lenses to encounter them and how to cope with them.

Last Update: January 2023

Contents<br>Introduction<br>Distortion<br>Field curvature<br>VignettingLight Falloff<br>Optical Vignetting<br>Color Cast

Spherical Aberration<br>Chromatic AberrationsLateral CA<br>Longitudinal CA

Coma<br>Astigmatism<br>Focus Shift<br>Onion ring bokeh<br>Flare resistanceGhosting<br>Internal reflections<br>Veiling flare

Further ReadingSupport UsBastianK<br>Latest posts by BastianK (see all)

Distortion

barrel distortion<br>pincushion distortion<br>complex/wavy distortion

Description: Straight lines in the picture are not straight but curved or bent.

Common problem in: zoom lenses and wide angle primes

Solution: "uniform" barrel or pincushion distortion can be easily corrected. For complex/wavy distortion though, lens correction profiles are mandatory, but not every correction profile works perfectly at every focusing distance.

You can also have a look at this article to find out how to create your own correction profiles for Lightroom/Photoshop.

Trivia: for today’s digital photography many lens manufacturers decided to correct this in post processing

Field curvature

Description: When you shoot a flat scene there is a dip in resolution/contrast in a part of the frame, e.g. the midframe area or the corners. In the example above you can see a lens that has higher corner resolution than midframe resolution.

Common problem in: wide angle lenses, some fast lenses

Solution: stopping down will usually reduce the field curvature. With some lenses focusing on the midframe instead of the center can also improve results.

Trivia: when taking a picture of a uniform yet structured surface you can use the "find edges" filter in Photoshop to make the shape of the field curvature visible.

W-shaped field curvature

Vignetting

Light Falloff

Description: Lower exposure in the corners compared to the center of the frame.

Common problem in: wide angle lenses, fast lenses

Solution: with most lenses stopping down will reduce the light falloff (with very small lenses there are sometimes only minor improvements)

Corner exposure can be lifted in post processing e.g. in Lightroom. For common lenses there are profiles available. Correcting this in post can lead to increased noise in the corners!

Trivia: on digital sensors some lenses (especially those with a small rear element close to the sensor) show increased light fall off due to "pixel vignetting" caused by the light rays hitting the sensor at an acute angle.

Optical Vignetting

Left: center, right: extreme corner<br>Description: the shape of out of focus light circles deteoriates towards the corners of the frame, so instead of circles you see shapes that resemble cat’s eyes.

Common problem in: (small) fast lenses

Solution: none (except for maybe buying a lens where this is less pronounced)

Stopping down you will eventually get a perfect circle at some point, but then you are shooting at e.g. f/2.8 instead of f/1.4.

Trivia: also often referred to as "mechanical vignetting"

Color Cast

uncorrected<br>corrected

Description: The corners of the frame take on a different color than the rest of the frame.

Common problem in: small wide angle lenses, especially mirrorless/rangefinder designs

Solution: correct it with the third party software "corner fix" or use flat field correction/gradients in Lightroom, for more details have a look at this article

Trivia: this is not exactly a lens aberration but rather the inability of digital sensors to capture light that hits them at a very acute angle.

Spherical Aberration

overcorrected<br>undercorrected<br>undercorrected (point light sources)

Description:

undercorrection: loss of contrast and resolution ("glow") across the whole frame

overcorrection: harsh bokeh with severe outlining

Common problem in: fast lenses (especially old ones) at maximum aperture

Solution: stopping the lens down by 1 stop usually makes a big difference

Trivia: for portraits a bit of undercorrected spherical aberration can be beneficial to give a smoother more flattering look

Chromatic Aberrations

Lateral CA

uncorrected<br>corrected

Crop from corner region of the frame

Description: the different color channels show different distortion patterns. Usually this leads to outlining on edges of high contrast that gets stronger the farther you move away from the center.

Common problem in: wide angle lenses, older tele lenses without ED elements, most zoom lenses.

Solution: in most cases this can be losslessly corrected in post. Stopping down does not make a difference to this aberration.

Trivia: Some lenses with a symmetrical optical design show zero lateral CA.

Longitudinal CA

overview<br>crop purple fringing<br>crop bokeh fringing

Description: Longitudinal chromatic aberrations come in...