Distortion Correction

An interesting article on DPReview, A Distorted View, looks at the use by camera manufacturers of in-camera correction of lens distortion. It concentrates on geometric distortion, but also mentions lateral chromatic aberration.

Lens designers can make simpler, smaller and lighter lenses by failing to correct some of these distortions, which can then be removed by software.  Overall this can result in higher image quality. Many camera manufacturers have taken this route and the examples on the site I think demonstrate how effective it is.

Generally these corrections are applied in-camera to jpegs, but RAW files are left RAW. Where manufacturers supply their own RAW conversion software, this will then apply similar corrections when processing the RAW files.

There are two problems here. Firstly few of us use the specific software for our cameras, because good though it may be, it lacks the workflow advantages of Lightroom (or Aperture)  so it is essential that the information about correcting the lenses is available for use by other programs. Some manufacturers currently are unwilling to share the necessary parameters, although these can fairly easily be found from a series of test exposures of a suitable subject.

Of course not all lenses we use with cameras that allow interchangeable lenses are made by the camera manufacturer. One statement that made me laugh was that about Sigma lenses where the feature states “no Sigma lenses currently require software correction.”  I currently own four Sigma lenses, and although for some purposes the images are fine without correction, every one of them requires software correction of both distortion and chromatic aberration for critical uses.  I would not dream for example of sending out a high-res image of an architectural subject without doing so.

One of Lightroom‘s major missing features is its lack of ability to correct distortion. I export images to Photoshop where I can use plugins including the excellent PTLens (which can also be used as an external editor for Lightroom) Panorama Tools and other software.

I’d like to see this built in to Lightroom, along with an automatic removal of chromatic aberration – the manual version works, but is time-consuming.

The 10.5mm Nikkor DC fisheye provides an extreme example of both chromatic aberration and also what can be achieved by way of software distortion correction, although of course the distortion here is an intentional feature.

© 2005 Peter Marshall.
Original 10.5mm fisheye file (Chromatic aberration corrected)

Correction to rectilinear using Panorama Tools
© 2005 Peter Marshall.
Correction using the Fish-eye Hemi plugin

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