Chromatic aberration, besides known as “color fringing” or “purple fringing”, is a mutual optical trouble that occurs when a lens is either unable to bring all wavelengths of color to the same focal plane, and/or when wavelengths of color are focused at dissimilar positions in the focal plane. Chromatic aberration is caused by lens dispersion, with different colors of light travelling at different speeds while passing through a lens. Equally a effect, the prototype tin look blurred or noticeable colored edges (ruddy, green, blue, yellowish, purple, magenta) can appear around objects, specially in high-contrast situations.
A perfect lens would focus all wavelengths into a single focal bespeak, where the best focus with the “circle of least defoliation” is located, every bit shown beneath:
In reality, the refractive alphabetize for each wavelength is different in lenses, which causes 2 types of Chromatic Aberration – Longitudinal Chromatic Aberration and Lateral Chromatic Aberration.
Longitudinal Chromatic Aberration
Longitudinal Chromatic Aberration, also known as “LoCA” or “bokeh fringing”, occurs when different wavelengths of colour practise not converge at the same point later on passing through a lens, as illustrated below:
Lenses with Longitudinal Chromatic Aberration problems tin can show fringing around objects throughout the prototype, even in the center. Red, Dark-green, Blue or a combination of these colors can appear around objects. Longitudinal Chromatic Aberration can exist dramatically reduced by stopping downwardly the lens. Fast aperture prime lenses are typically much more prone to LoCA than slower lenses.
Hither is an example of longitudinal chromatic abnormality that is visible at dissimilar distances:
Notation the greenish color on the acme of the image, transforming to neutral in the middle, and so becoming purple on the bottom part of the prototype that is closer to the camera. This kind of longitudinal chromatic aberration is present even on high-end, expensive lenses like the Nikon 35mm f/ane.4G. This type of LoCA / bokeh fringing can be significantly reduced in postal service-processing. For example, Lightroom 4.ane has the “De-Fringe tool”, which allows one to select an eye dropper under the “Lens Corrections” module and pick a fringe color that needs to be corrected. With such tool, 1 tin can either completely eliminate this type of fringing or reduce it significantly.
Hither is some other case of longitudinal chromatic abnormality with green and purple fringing, visible on both sides of the tree trunks and branches:
The bottom crop was corrected in Lightroom’s “Lens Corrections” sub-module with a single click. The same can be done in Photoshop, but involves more steps (if non using the Photographic camera RAW tool).
Lateral Chromatic Aberration
Lateral Chromatic Aberration, also known as “transverse chromatic aberration”, occurs when different wavelengths of colour coming at an angle focus at different positions along the same focal plane, as illustrated below:
Unlike LoCA, Lateral Chromatic Aberration never shows upwardly in the heart and is only visible towards the corners of the image in high-contrast areas. Blue and purple fringing is frequently common on some fisheye, wide-bending and low-quality lenses. Unlike Longitudinal Chromatic Aberration, Lateral Chromatic Aberration cannot be removed by stopping down the lens, but can be removed or reduced in mail service-processing software.
Here is a corner ingather from the Nikon 35mm f/1.8G lens that has a rather astringent amount of lateral CA in the corners:
Unfortunately, many lenses accept both longitudinal and lateral chromatic aberrations present at the same time. The only way to reduce these aberrations, is to end downwardly the lens (to reduce LoCA) and and then fix lateral CA in post-processing software like Lightroom and Photoshop.
While many mod lens manufacturers utilise specific techniques to reduce chromatic aberrations using achromatic/apochromatic optical designs and special extra-low dispersion elements, chromatic aberration is still an issue on virtually prime and zoom lenses that nosotros simply take to larn how to become around with. The good news is that many modernistic DSLRs incorporate special in-camera postal service-processing techniques to reduce and fifty-fifty eliminate lens chromatic aberrations and plenty of software packages are besides capable of dealing with chromatic aberrations.
If you are interested in reading more than, below is the list of articles on other types of aberrations and issues that we take previously published on Photography Life:
- Spherical Abnormality
- Field Curvature
- Ghosting / Flare
- Focus Shift