Photofocus

Guest Photo & Post By www.NatCoalson.com – Follow Nat on Twitter

One of the most exciting features introduced in Lightroom 3 is the new Lens Corrections panel. These controls allow you to correct optical distortion and other lens artifacts such as chromatic aberration and vignetting.

This is a big step forward in image editing. Until recently, to fix distortion in a photo you had to use pixel-based editing software such as Photoshop, which can significantly degrade image quality.
Lightroom uses metadata to perform all adjustments on photos. The original image data on disk is never altered, which allows you to make an unlimited number of adjustments to an image without affecting quality and provides for unlimited “undo’s”.

Note: I always capture in raw format, and I want to work with the raw images as far through my workflow as possible. With Lightroom’s Lens Corrections I can significantly improve the effects of lens distortion and artifacts directly on the raw image data. However, you can also apply the same lens corrections to any of the file formats that Lightroom supports, including JPG and even layered TIF files.

Defining the problem

Nearly all camera lenses introduce some amount of distortion to a captured image. The most common types of distortion are perspective distortion, which produces converging lines that should be vertical, and barrel and pincushion distortion, spherical distortions that make the photo appear to either bulge outward or pinch inward. These distortions are often caused by wide angle lenses and are most easily seen around the edges of the frame. With Lightroom 3 you can fix most kinds of lens distortion. See the above images for a before and after example.

Chromatic aberration (CA) is a lens artifact that results in color fringing around the edges of object. It happens when different wavelengths of light strike the camera sensor at different points. Some lenses produce much more chromatic aberration than others. Figure 3 shows severe chromatic aberration in the red/cyan channel. This is easily fixed in Lightroom.

TIP: When possible, check every image for CA – it’s present in more captures than you might expect. You usually need to zoom in very close to see CA.

Vignetting refers to darkening around the corners and edges of an image. Again, it’s most commonly seen in photos made with wide angle lenses.

Using the Lens Corrections Panel

With an image loaded in Lightroom’s Develop module, open the Lens Corrections panel, which is about halfway down the right panel group. There are two modes for the panel, Profile and Manual, shown in text buttons at the top. The default view is Profile. You can use one or the other, or both modes together, to apply your desired corrections.

Profile mode lets you choose a lens profile for Lightroom to automatically apply corrections specific to that lens. To start, check the box to Enable Profile Corrections. Lightroom uses the EXIF metadata in the capture to determine what profile to use.

Lightroom ships with profiles for many lenses, and new profiles are being created all the time. However, there are still many lenses out there that have not yet been profiled. If you check the box to Enable Profile Corrections and the dropdown menus below remain blank, it means that Lightroom could not find a profile for your specific lens. You can manually choose another profile if there’s a lens that’s similar to yours.

You can also make your own lens profiles but this is a very laborious process. Even so, many photographers are creating custom lens profiles and sharing them online. You can learn more about lens profiles and the Lens Profile Creator and Downloader applications at http://labs.adobe.com/technologies/lensprofile_creator/

Below the dropdown menus for profile selection are three sliders: Distortion, C. Aberration and Vignetting. These sliders let you adjust the amount of each adjustment being applied by the profile. They all default to 100; drag the slider to the left to decrease that adjustment or to the right to increase it.

TIP: use the tiny switch at the top left of the Lens Corrections panel to enable/disable the effects of the panel.

Manual mode allows you to make much more dramatic adjustments to the image. You can use Manual adjustments after applying a profile; all the settings work together to produce the finished result. The easiest way to learn how these sliders work is just to try them! Click and drag each slider to see its effect on the photo.

When examined closely, you’ll find that most captures will exhibit one or more of the problems described above. With Lightroom 3, you can dramatically improve your photos using the Lens Corrections panel. You can read more about Lens Corrections in my Lightroom 3 book.

Nat is the author of Lightroom 3: Streamlining Your Digital Photography Process.

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