Trying to go wider than 10mm on crop or 16mm on full frame, you will see heavy wide angle distortions. It won't be as extreme as a fisheye, but it's just optically impossible to correct it all away.
The best solution, besides some highly specialized cameras that swing the lens while the shutter is open, or somthing similar, is stitching. That doesn't need to be all that complicated.... This image is a quick, three-image composite that was done on the spur of the moment at a client's request...
This was shot with 7D, Tokina 12-24 (not
set at it's widest focal length, tho I don't recall exactly where I set it). The hedge seen toward either lower corner actually runs straight across right in front of where I was standing to take the shots, so this is nearly a 180 degree angle of view. The center of the image was kept open for a title to be added later (about where my watermark is seen here).
It was dead simple to combine the images in Photoshop. The biggest problem? There was someone walking across the scene as I was making the three separate shots (handheld), and they showed up three times in the final image. A little cloning fixed that! After stitching, the edges of the final image are always jagged and curved, so I allowed a bit of extra room framing the three original shots, to be able to crop the final composite to a wide rectangle.
If you want to go crazy with stitching, check out "gigapan" photography, where as many as 200 and more images are combined into a single image that's a full gigabyte or more. There's www.gigapan.org
website, which, among others, features some of the work of George Lepp
. He often uses a telephoto, such as a 70-200 zoom, to make a fantastic, huge, very wide images. He's also experimented with macro gigpan.