Peter Schulz demonstrates the corrective power of Panorama Tools, a free Windows utility. Excerpt:
When shooting underwater, the effects of wide angle distortion are often not noticeable because, unlike buildings, there are few straight lines. After all, who knows how round a French Angelfish really is. But with wrecks and panoramic reef shots distortion becomes very noticeable.
Fortunately there is a software fix for this problem. It’s called PanoTools. PanoTools plugins are available for Adobe PS, Adobe Elements, and Paint Shop Pro that run on Windows, Mac, and Linux platforms. And the plugins are free!