Why Aperture has a very nice collection of image adjustment tools, it lacks the ability to perform any kind of distortion correction. If you’re shooting with a wide-angle lens that has trouble with barrel distortion, then you won’t have any way to correct these issues inside Aperture. Photoshop provides excellent barrel and pincushion distortion through the Lens Correction filter, but if you don’t have Photoshop you’re out of luck.
LensTweaker, a $30 application from TweakerSoft.com gives you a simple way to perform barrel and pincusion distortion. LensTweaker provides an interface consisting of a single dialog box that provides sliders for adding either barrel or pincushion warping to an image. So, if your image has a bit of barrel distortion, you would warp it back to normal by adding a little pinchushioning.
LensTweaker provides two different sliders with different degrees of effect. The first slider is fairly coarse and allows you to make broad changes to your image. The second slider adds a degree of fine-tuning.
For automatic correction, LensTweaker allows you to profile a specific lens at a particular focal length. To profile a lens, you print out a test pattern and then shoot a picture of it with the lens at the appropriate focal length. LensTweaker provides an assistant that will analyze that image and create a profile designed specifically to remove the appropriate distortion from images shot with that lens at that focal length.
LensTweaker can’t handle raw files, so you’ll have to tell Aperture to export versions in TIFF or JPEG format. You can then correct these images in LensTweaker and import the results back into Aperture (or you could define LensTweaker as your External Editor, and round-trip your images from Aperture into LensTweaker). LensTweaker also provides straightening controls, and some simple image adjustments, though you’ll probably want to perform these operations in Aperture.
Most images that suffer from barrel distortion also have trouble with vignetting. Unfortunately, LensTweaker offers no tools for vignette correction, and neither does Aperture. Photoshop’s Lens Correction filter remains the best way to remove vignetting.
LensTweaker delivers good quality, although extreme corrections can end up a little soft. It’s definitely not suitable for dealing with extreme corrections, such as turning a fisheye image into a corrected rectilinear image. For 30 bucks, though, it offers a handy feature that Aperture sorely needs, and checking out the free demo is time well-spent.