Hi Del,
I have used the Sigma 15mm fisheye on my Fuji S-2 for three years now and have to say I have been surprisingly happy with it, for several reasons.
First, the lens itself was about 900 dollars cheaper than a good equivalent straight-line lens. That, of course, was the main reason I bought it.
Second, even with the Photoshop fixing, it is very sharp to the corners and illumination is even. I guess once a lens designer realizes he doesn't have to worry about making straight lines straight, he can do a lot better on the other characteristics a good lens needs.
Third, it is smaller and lighter than, say, a 14mm Nikkor, and I can be a little more "direct" in handling it when I pull it out of the camera bag. (Fewer worries about scratching a very big, very expensive front element!)
Fourth, and this was another surprise, there are a lot of times when fisheye really looks better than straight wide angle. Obviously, if you need your building facade to look square, it needs to look square. But I've been in many situations where the slight fisheye actually looked MORE natural than straight-line. Just one example: In a random crowd of people, the folks in the corners won't have egg-shaped heads. Their bodies might be bowed, but they won't look fat and top-heavy. I suppose this is a long way of saying that, at extreme wide angle, everything has got some kind of distortion, so it's just a matter of picking your poison.
The current Photoshop contains a lens distortion filter, but I can't get it to work with this lens, so I stick to my original choice of software, "Debarrelizer" by The Imaging Factory. I think it's 30 or 40 bucks, very easy to use, and can be set as an action in Photoshop to correct a whole batch of files at once.
A few times I have used software based on the amazing PanoTools program to fix distortion in only one direction. Result: the look of a scanning panoramic camera. (Of course you could do this with a regular lens, too.)
Drawbacks. Well, there's the obvious need for Photoshop correction, should you elect to straighten. The correction means that parts of the picture will get shaved off. It's pretty easy to tell what's going to go, but that does mean you'll have yet another thing to think about while you shoot.
One effect I hadn't predicted was that the final aspect ratio of the photo will be different than the original 2:3. Because more gets trimmed on the longer dimension, the finished aspect ratio will be closer to 2:3.5.
Keep in mind that the results I'm talking about are based on a full-frame (35mm) fisheye lens used on a camera with 1.5 focal length multiplier, so the original files are not all THAT fisheye to start with. I think if you're considering the 10.5 mm Nikon fisheye, the story is different. That lens is designed for the APS sensor, so getting straight line out of it would call for a lot more nipping and tucking. (I understand that the Nikon software will do that for you if you're shooting on a Nikon camera.) I have heard that digital interpolation is an issue for getting that lens to "go straight."
Hope this helps. MB
