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Correcting Lens Distortion

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For this tutorial I've used Adobe Photoshop CS4, but similar features can be found in most other good quality image editing programs, including recent versions of Photoshop Elements and Corel Paint Shop Pro.

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Not all cameras are created equal, and the main reason that a £250 digital compact will usually produce better pictures than one costing £65 is the quality of the lens. Cheaper cameras generally have lower quality optics, and can suffer from a number of problems that have a negative effect image quality.

The most noticeable sign of a cheaper lens is excessive distortion at the wide-angle end of the zoom range. This causes what should be straight parallel lines to appear curved as though the centre of the image was bowed out toward the camera like the side of a barrel. The effect is also noticeable on close-range wide-angle portrait shots, making your subject's facial features appear distorted. This is one of the reasons why I always test the wide-angle distortion of the lens in my cameras reviews with a shot like the one below.



This shot was taken with a low-cost compact camera, and as you can see clearly see the effect of barrel distortion, most clearly around the edges of the picture. Less often seen but just as annoying is the exact opposite of barrel distortion; pincushion distortion, which is sometimes an unwanted feature of the very long telephoto zoom lenses found on the more extreme super-zoom cameras. In the shot below, pincushion distortion causes the edges of the horizon to curve upwards.



Another problem associated with lower quality lenses, and one which also shows up frequently in camera reviews, is chromatic aberration. I've covered this effect in some detail in a previous tutorial, but it bears mentioning again. Chromatic aberration shows up as red and cyan (or more rarely blue and yellow) fringes around brighter areas, most noticeably in the corners of the frame. You can see this effect in a full-resolution crop from the picture of the garden wall above.



While a better quality lens would reduce such distortion effects, some recent cameras, particularly the up-market models, have included automatic distortion correction, which processes the image in-camera to remove the effects of lens distortion. However it is possible enjoy distortion-free images by manually correcting optical errors using photo editing software. With a bit of tweaking our optically distorted garden wall can come out looking like this:



And the fishing boat can look like this:



Both of those transformations were done in five minutes using a couple of simple Photoshop tools. Keep reading to see how it's done.

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