Despite the dramatic improvement in the optical quality of modern lenses, common lens issues such as pin-cushion and barrel distortion, as well as vignetting, are still widespread.
Ironically, this is often the result of the very optical improvements mentioned, as manufacturers attempt to produce zoom lenses with ever-greater ranges in increasingly smaller sizes. Asking so much of a compact zoom lens is bound to result in distortions and aberrations at one or both ends of the range.
Fortunately, such lens issues are easily addressed in Raw processors, and in some cases are fixed automatically if the Raw processor recognises the lens profile. If not, manual correction is straightforward, and you can save the changes to be made easily next time.
This type of colour fringing occurs when the lens is unable to focus the red, green, and blue wavelengths equally at the same point. Adjusting either the Red/Cyan or Blue/Yellow slider in the tool panel is all it usually requires.
This type of distortion occurs most often at the telephoto end of a zoom lens, and is observed in straight lines bending in toward the centre of the frame.
This distortion will occur mostly at wide angles, and is characterised by straight lines that bend out toward the edges of the frame.
Straight, parallel lines
Both issues can be quickly fixed during Raw processing with the relevant controls (Distortion slider in Lightroom) or plug-ins. The image is properly corrected when straight lines run parallel to the edges of the frame.
Fixing dark corners
Vignetting occurs when light is prevented from fully reaching the corners of the frame. It is usually caused by the lens barrel or lens hood, or by light striking the lens at an angle, and is most noticeable in areas of even tone, such as a blue sky, which will appear visibly darker at the corners of the frame. Use the vignette control to lighten the corners.
Vignetting can also be used creatively to draw the viewer’s eye to the subject of a picture. Usually corners are darkened and the shape and size of the vignette adjusted to best fit the subject. However, we can slide the vignette control the other way to deliberately lighten the corners for a more dreamy effect.
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