Lens Distortion and Aberration
Written by Abin Alex and Anu Joseph.
Abstract
No real lens is perfect. Distortion bends straight lines, aberration blurs or colours the image, and vignetting darkens the corners. This guide describes barrel, pincushion and moustache distortion, perspective distortion, chromatic aberration, and spherical aberration, coma, astigmatism and field curvature. It explains how lens design and software reduce these faults, though no lens removes them all, and what the labels ED, ASPH and APO mean. It is written for photographers and cinematographers who need to recognise a fault and decide what to do about it.
Keywords: lens distortion; chromatic aberration; vignetting; barrel distortion; aspherical lens
- What are lens distortion and lens aberration?
- What are barrel, pincushion and moustache distortion?
- What is perspective distortion?
- What is chromatic aberration?
- What are spherical aberration, coma, astigmatism and field curvature?
- What is vignetting?
- How can you reduce distortion and aberration?
- What do ED, ASPH and APO on a lens mean?
What are lens distortion and lens aberration?
Short answer. Distortion changes the shape of the picture, so straight lines look curved. Aberration spreads the light from one point of the subject over an area, so the image looks soft or has colour fringes. Vignetting darkens the edges.
- A perfect lens would keep straight lines straight and bring every colour to the same point. Real lenses bend lines outward or inward from the centre.
- Aberration happens when light from one point of the subject does not meet in a single point after passing through the lens, so the image is blurred or distorted.
- Aberrations are of two kinds: chromatic, which depends on colour, and monochromatic, which depends on the geometry of the lens and appears even in single-colour light.
- Wider lenses show more distortion, and fisheye lenses show it strongly.
| Fault | What you see | Main cause |
|---|---|---|
| Distortion | Straight lines look curved | Lens design, or camera position |
| Chromatic aberration | Colour fringes on edges | Glass bends each colour differently |
| Spherical aberration, coma, astigmatism, field curvature | Soft or smeared detail | Lens surface shape |
| Vignetting | Dark corners | Lens design or accessories |
Table 1. The main lens faults at a glance.
Cham tipTest your own lens first. Shoot a brick wall or a window frame at the widest and longest settings and look at the edges.
Cham taskShoot a window frame or a tiled wall at your widest zoom setting. Mark which lines curve and which way they bend.
Check yourself: What is the difference between distortion and aberration?
Distortion bends the shape of straight lines. Aberration blurs the image or adds colour fringes.
What are barrel, pincushion and moustache distortion?
Short answer. Optical distortion comes from the design of the lens and is also called lens distortion. Barrel distortion bows lines outward. Pincushion distortion bends them inward. Moustache distortion mixes both.
- Barrel distortion makes rectangles look barrel-shaped. It is typical of wide-angle lenses and the short end of zoom lenses.
- Pincushion distortion makes lines bend inward toward the centre. It is typical of telephoto lenses and the long end of zoom lenses.
- Moustache distortion, also called wavy or complex distortion, curves lines inward near the centre and outward at the corners. It is the hardest type to correct.
- Distortion is more common in zoom lenses and can change as the focal length changes.
- Many people say convex and concave for barrel and pincushion. Use barrel and pincushion instead, because convex and concave also name lens shapes.
Cham tipName it by the line shape you see: bulging out is barrel, pulling in is pincushion, wavy is moustache.
Cham taskShoot the same bookshelf at the shortest and the longest focal length of a zoom. Compare how the shelf edges bend.
Check yourself: Which type of distortion do wide-angle lenses usually show?
Barrel distortion, where lines bow outward.
What is perspective distortion?
Short answer. Perspective distortion comes from where the camera stands, not from the glass. When you shoot from very close with a wide view, the subject looks unnatural.
- Optical distortion is caused by lens design. Perspective distortion is caused by the position of the camera relative to the subject, or by where the subject sits in the frame.
- It appears when the focal length or field of view differs strongly from normal vision.
- Changing the distance between camera and subject, the camera angle or the focal length can reduce it.
- Even a standard 50 mm prime lens can show barrel distortion at very close distances.
- The Focal Length guide shows how camera distance changes perspective.
Cham tipIf a face looks odd, move the camera back before changing anything else.
Cham taskPhotograph one friend from 0.5 m with a wide lens and from 2 m with a longer lens. Compare the faces.
Check yourself: Can perspective distortion be fixed by buying a better lens?
Not usually. It depends on camera position, so change distance, angle or focal length.
What is chromatic aberration?
Short answer. Chromatic aberration is a failure of a lens to focus all colours at the same point. Glass bends each wavelength by a different amount, so colour fringes appear on high-contrast edges (Ray, 2002).
- The cause is dispersion. A lens has a different refractive index for each wavelength, so red, green and blue light turn through different angles.
- Longitudinal chromatic aberration focuses colours at different points along the optical axis. It can appear in the centre or at the edges, and it is stronger on fast, wide-aperture prime lenses.
- Lateral, or transverse, chromatic aberration focuses colours at different positions on the same focal plane. It never appears in the centre, only toward the corners.
- Stopping down by one or two stops reduces longitudinal aberration. It does not remove lateral aberration, which software can reduce.
- Fringes are often blue, purple, green or magenta, and appear around objects in high-contrast scenes.
| Type | Where colours separate | Where it shows | Stopping down helps? |
|---|---|---|---|
| Longitudinal | Along the optical axis | Centre or edges | Yes |
| Lateral | Across the focal plane | Corners only | No |
Table 2. The two kinds of chromatic aberration.
Cham tipShoot RAW so you can remove fringes later, and avoid placing the key subject in the extreme corner.
Cham taskShoot a dark branch against a bright sky at f/1.8 and at f/5.6. Zoom in on the edges and compare the colour fringes.
Check yourself: Which chromatic aberration can you reduce by stopping down?
Longitudinal chromatic aberration.
What are spherical aberration, coma, astigmatism and field curvature?
Short answer. Monochromatic aberrations are caused by the geometry of the lens and occur even in light of one colour. They include defocus, spherical aberration, coma, astigmatism, field curvature and image distortion (Ray, 2002).
- Defocus means the image is out of focus along the optical axis. It lowers sharpness and contrast, and focus adjustment exists to minimise it.
- Spherical aberration happens when rays through the edge of a lens focus at a different point from rays near the axis. It reduces resolution and clarity.
- Coma makes off-axis points of light look like a comet with a tail. A lens with coma can be sharp in the centre and softer toward the edges.
- Astigmatism means rays in two perpendicular planes have different focus points.
- Field curvature means the sharpest focus lies on a curved surface, not a flat plane. The centre and edges are then never sharp together.
| Aberration | What you see |
|---|---|
| Defocus | Overall soft image, low contrast |
| Spherical aberration | Soft, hazy detail |
| Coma | Comet-shaped points of light near the edges |
| Astigmatism | Points of light stretched in one direction |
| Field curvature | Centre sharp while edges soften, or the reverse |
Table 3. Monochromatic aberrations.
Cham tipCheck the corners with point lights at night. Coma and astigmatism show there first.
Cham taskPhotograph distant street lights at your widest aperture. Compare the centre lights with the corner lights.
Check yourself: What is coma?
An aberration where off-axis points of light spread into a comet-shaped tail.
What is vignetting?
Short answer. Vignetting is a darkening of the image toward the edges, also called light fall-off. Optical vignetting comes from the lens design, and mechanical vignetting comes from accessories that block light.
- All lenses make an image that is darker at the edges than in the centre.
- Mechanical vignetting appears when filters, hoods or third-party extensions block some light before it reaches the sensor.
- Many cameras can correct vignetting in-camera. The menu names differ: Peripheral Illumination Correction on Canon, vignette control on Nikon, and shading compensation on Sony.
- In-camera correction works well for JPEG files. For RAW files, raw editors such as Lightroom and Photoshop use their own lens-correction profiles.
- Vignetting can also be added on purpose in editing to draw the eye to the centre.
Cham tipIf corners go dark with a filter on, take the filter off and compare. That is the fastest test.
Cham taskShoot a plain wall or cloudy sky at f/2 with and without a lens hood. Compare the corners.
Check yourself: What is the difference between optical and mechanical vignetting?
Optical vignetting comes from the lens design. Mechanical vignetting comes from accessories that block light.
How can you reduce distortion and aberration?
Short answer. Lens makers reduce faults with special glass and shapes, and photographers reduce them by choosing settings carefully and correcting in software.
- Optical distortion can be reduced by compensating elements, but removing it completely is nearly impossible.
- Aspherical (ASPH) elements reduce distortion and spherical aberration. Low-dispersion glass (ED, LD, SLD, UD and similar) reduces chromatic aberration.
- Several elements work together, so the fault of one is cancelled by another.
- In the field: avoid extreme focal lengths on zoom lenses, stop down one or two stops, keep straight lines near the centre, and avoid high-contrast scenes where colour fringes appear.
- In software: Photoshop has Filter, Distort, Lens Correction, with chromatic aberration controls. Lightroom can save a lens-correction setting as a template for imported RAW files.
- Shoot RAW so that you can correct fringes, vignetting and distortion later.
Cham tipCorrect in software last, not first. Choose the right lens and aperture for the shot, then clean up.
Cham taskOpen a RAW photo with visible fringes. Turn lens correction and chromatic aberration removal on and off and compare.
Check yourself: Which two lens codes reduce chromatic aberration?
Low-dispersion glass codes such as ED, LD, SLD or UD.
What do ED, ASPH and APO on a lens mean?
Short answer. Lens makers print short codes on the barrel to show special glass. Most codes show reduced chromatic aberration, and ASPH shows an aspherical element. Brand names differ, so check the maker's guide.
- Codes such as LD, ED, ELD, SLD and ULD or UD show low-dispersion glass that reduces colour fringing and chromatic aberration.
- ASPH marks an aspherical element, which reduces distortion and spherical aberration.
- APO, short for apochromatic, marks better correction of chromatic and spherical aberration than a common achromatic lens.
- Tamron uses XLD and HID, and Tokina uses SD, for similar glass types.
| Code | Meaning |
|---|---|
| ASPH | Aspherical element |
| LD / ED / ELD / SLD / ULD / UD | Low-dispersion glass of different grades |
| XLD | Extra-low dispersion (Tamron) |
| SD | Super-low dispersion (Tokina) |
| APO | Apochromatic correction |
Table 4. Common correction codes on lenses.
Cham tipMore codes do not always mean a better lens. Check sample photos of the edges and corners.
Cham taskLook at two of your own lenses. Write down every code on the barrel and look up its meaning.
Check yourself: What does ASPH mean?
An aspherical lens element that reduces distortion and spherical aberration.
Questions beginners ask
What is the difference between distortion and aberration?
Distortion changes the shape of straight lines. Aberration spreads light so the image is soft or has colour fringes.
Why do wide-angle lenses show barrel distortion?
Wide-angle designs bend rays strongly to cover a large field, and barrel distortion is a common result. It is also strongest at the short end of a zoom lens.
Can I fix chromatic aberration in editing?
Yes, in most cases. Lateral chromatic aberration is easy to remove in software. Longitudinal aberration is harder because it is a focus error.
Does stopping down reduce aberration?
It reduces longitudinal chromatic aberration and some other faults. It does not remove lateral chromatic aberration.
What is vignetting?
Vignetting is a darkening of the image toward the edges. It comes from the lens design or from accessories such as filters and hoods.
Why shoot RAW to correct lens faults?
A RAW file keeps all the data, so editing software can correct distortion, fringes and vignetting without losing quality.
References
- Ray, S.F. (2002) Applied Photographic Optics. 3rd edn. Oxford: Focal Press.
How to cite this guide. Alex, A., & Joseph, A. (2026). Lens distortion and aberration: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/lens-distortion-and-aberration/
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