Not as in "defishing is good on the lake today," but as in removing the distortion that makes a fisheye lens a fisheye and not a rectilinear lens.

Initial image

This image like so many of the images I shoot with my fisheye lens is intended to be fun. Hence my feet. I am sure at some point I will get tired of the "my feet" in the image shots, but as of yet, I am still having fun with the lens.

This image was shot with the Canon EF 15mm f/2.8 full frame fisheye. The image has been resized for this page view, but not corrected geometrically in any way.

Defishing

I use Photoshop CS to edit most of my images. Photoshop contains no intrinsic mechanism to remove fisheye distortions in an image, but a simple to use plugin from ePaperPress called PTLens can help remove the characteristic distortions. The PTLens plugin is free on the internet, and works well by my simple tests. It would be a good place to start with defishing your images. Used as a plugin, the PTLens routine determines the camera, focal length and lens used and applies predetermined correction to the image.  I do not know what versions of Photoshop the plugin is compatible with as I have only tested it with Photoshop CS. During the defish process, you will lose some of the image. In the original image you can see the San Francisco Bay in the upper left corner as well as a tree and sidewalk. They are gone in the defished image.

This is the same image having been "defished" with PTLens. Notice the curvatures in what should be straight is gone when compared to the initial image.

Perspective correction

Even though the image has been defished the image has a lot of perspective issues that you may want to correct. If you will look at the image above, you will see that there are many elements that should be parallel and square but are not. For example, the wall to the right of my feet should be parallel to the left edge of the left most skylight. Using Photoshop I have corrected the perspective and the results are below.

Using Transform | Perspective in Photoshop I created the image above. Yes, it is square, but look how much image was lost.

Discussion

While I love the fisheye lens, I don't recommend it if you intend to defish all your images. If you do, you should buy a rectilinear lens and get a better image to start with as opposed to one that will need correction. In fact, so much image is lost, that I wonder what the focal length equivalent in a rectilinear lens would be. If you know, drop me a line. Does this mean that the lens is without use or purpose. Not at all, but you need to like or want the fisheye look to be truly happy with the lens. I defished many of my early images because I wanted to know how, and to see how they looked. After doing a few, I haven't done any more. I for one like the fish look!