Photoshop CS2 contains a versatile tool for correction certain problems caused by camera lenses. You can find it under Filters > Distort > Lens Correction.
One option for this tool brightens and darkens the corners of images in order to compensate for lens vignetting.
The nice thing about this tool is that it acts as if all images are actually square. The lens vignette tool is not fooled by widescreen aspect ratios. Lenses are round, and so is the vignette correction.
You'd think Photoshop would adopt this outlook for the other related tools as well. Oddly enough, it does not.
Here's a widescreen image being subjected to Photoshop CS2's barrel distortion / pincushion distortion correction tool.
Notice how the effect is nailed to the corners of the image. That's an odd thing to do. Lenses are round. Barrel distortion and pincushioning should be nailed to the corners of a virtual square image, not the true corners of the actual widescreen image.
It seems a more sensible approach would be to use the Image > Canvas Size options to extend the widescreen image onto a square canvas before applying lens distortion effects.
