A perfect lens would render straight lines as straight, no matter where they occur. Most practical lenses aren’t that good, though, and instead bend lines outwards (barrel distortion) or inwards (pincushion distortion). Wide-angle lenses and wide-range zoom lenses often suffer particularly badly from this.
Why does it matter?
1. Straight lines
Distorted image
Architectural photographers are well-known for seeking to avoid geometric distortion. It’s easy to understand that distortion will be readily noticeable when shooting objects with straight lines. 2. People
The human brain is remarkably good at recognizing human faces, and can readily detect when someone has gained or lost weight, for example, just by looking at the face. The same is true for geometric distortion.
How complex is it to correct?
1. Simple distortion: Barrel or pincushion
Distortion free image
Barel distortion
Pincushion distortion
Most photographers will be aware of the barrel and pincushion distortion that typically appear at the shorter and longer ends of a zoom lens respectively, with continuous variation in between. 2. Higher order distortion
Complex distortion
Real-world lenses often exhibit a distortion pattern that, even within a single image, varies from barrel to pincushion across the field. The effect of such lens design is to have a maximum distortion mid-field, while the edges display little or virtually no distortion. 3. Focus dependence
Original image
Distortion correction when focusing
distance is not taken into account
DxO Optics Pro correction
(takes focus distance into account)
(Nikon D70 and Sigma 15 mm f/2.8 EX Diagonal Fisheye)
Some modern lenses exhibit geometric distortion that varies with focusing distance. As a result, this distortion can only be properly corrected using correction models that take account of focusing distance, as shown in the example. 4. Color plane specific
Lateral chromatic aberration
DxO Optics Pro Correction
(Sony F828)
Distortion affects different parts of the color spectrum differently (prism effect) and creates the so called "lateral chromatic aberration", which results in color fringes arround high/low-light transitions. With the ever increasing sensor resolutions, lateral chromatic aberration becomes more and more visible, in turn making it more and more important to precisely address distortion for each color plane.
DxO Optics Engine includes calibrated, camera-specific corrections for supported lens/body combinations.
Correction of geometric distortion & chromatic aberration
A number of modern software products (even freewares) address the simple types of distortion quite successfully. However, when the distortion is more complex, varies with focus, and depends on the color plane, as is the case with a growing number of modern lenses, DxO is the only solution that can handle it.
original image
DxO Optics Pro correction
(Canon EOS 1D Mark II and Sigma 15mm Fisheye)
Photo: Cyrille de la Chesnay
Furthermore, for any lenses (from fisheye to telephoto), DxO Optics Pro corrects distortion automatically (residual distortion < 0.15%), enabling batch processing. Circular fisheye correction
DxO Optics Pro version 4 expands the correction of geometrical distortion to a number of camera body and circular fish-eye combinations, opening up whole new creative possibilities with these special-purpose lenses.
Retain the broad sweep of your fish-eye vision without the accompanying extreme geometric distortion.
Original image
Circular fisheye correction by DxO Optics Pro
Photo: Thomas Jolivet
The distortion of circular fisheyes is so extreme that just being able to “de-fish” them represents, in itself, a truly extraordinary achievement!
