Aspherical lenses offer better correction for many common lens aberrations than regular spherical lenses. Lenses with a spherical profile are easier to grind into the correct shape, but aspherical lenses have a more complex profile that’s more difficult and more expensive to make. Many modern lenses use moulded aspherical elements instead to get round this. […]
Lens aberrations explained
No camera lens is optically perfect. In order to offer the focal lengths, zoom ranges, maximum apertures, sizes or prices that people want, the designers have to make some compromises. This means that all lenses exhibit 'aberrations' to some degree. Typically this may involve distortion, where straight lines start to appear bowed, chromatic aberration, or colour fringing, around object edges, and corner shading or vignetting, where the edges or corners of a picture are darker than the centre.
Here's a selection of topics explaining a little more about aberrations and what lens designers can do about them.
Apochromatic lens
An apochromatic (APO) lens is designed to offer improved correction of chromatic aberration and spherical aberration using specialised materials and combinations of lens elements. It’s a selling point for lenses, though only indicates the lens design used and isn’t really a guarantee of good performance on its own.
Volume deformation or anamorphosis
A special type of distortion correction once built into DxO Optics Pro but now built into the separate DxO ViewPoint application. It fixes the distortion usually seen with wideangle lenses where objects near the edge of the frame appear disproportionately wide – it’s most obvious with human figures.
Vignette
An effect where the edges of the picture are darker than the centre. It was common with old lenses and it’s become associated with a vintage look. It’s considered a lens aberration these days, though photographers often like to add a vignette effect deliberately.
Pincushion distortion
This is where straight lines near the edge of the picture appear to bow inwards. It’s not as common as barrel distortion, but you do see it quite a lot with telephoto zoom lenses when the lens is set to its maximum focal length. You may not notice it with many types of subject, but […]
Lens profile
Almost all lenses suffer from aberrations, including distortion, chromatic aberration and vignetting. These are difficult to eliminate optically in the lens design, so software publishers are increasingly offering lens correction profiles to do this digitally. The software can identify the lens used from the image’s EXIF data and then find and apply the correct profile […]
Lens Modulation Optimizer (LMO)
A processing algorithm used by Fuji in some of its cameras to counteract the softening effects of diffraction at small lens apertures, and image softness at the edge of the frame. It seems likely the LMO is simply applying some intelligent sharpening.
Lens corrections
Lenses aren’t perfect – they all have optical aberrations of one sort or another. Now, though, many software applications have lens correction to correct these digitally, either with manual controls or automatic lens correction profiles.
Distortion
An optical effect in some lenses where straight lines come out slightly bowed. You often see ‘barrel distortion’ with wideangle lenses or ‘pincushion distortion’ with telephoto lenses at their longest zoom setting. More expensive lenses tend to have less distortion but, generally, the longer the lens’s zoom range the more likely you are to see […]
Chromatic aberration
This is a lens aberration that produces colour fringing around the outlines of objects near the edges of the picture. It’s very hard to eradicate completely from lens designs without making them extremely complex or expensive, but it is possible to correct chromatic aberration using software and many cameras will now correct it automatically as […]
Barrel distortion
This is where straight lines near the edge of the picture appear to bow outwards, and you see this a lot with zoom lenses at their wideangle setting. It’s most noticeable if the horizon is near the top or bottom of the picture. Barrel distortion is very difficult to eradicate completely from the lens design, […]