Using a fisheye lens can be a little confusing at first. You're used to seeing straight lines rendered straight in your images, so the composition you envision in your head may not be anywhere close to what appears when you view the image the camera takes. The only part of the scene that doesn't suffer sever distortion is what's directly in front of the lens. Keep this in mind if you're trying to capture a face, figure or other sharp subject in the distorted scene you're capturing.
Like any photographic effect, the distortion that may throw off your early compositions can work to your advantage as you get used to the lens. Experiment with photographing geometric subjects such as bridges, towers and other spidery objects. Since the fisheye lens has variable amounts of distortion, slight shifts in camera position can produce a range of images.
Shooting fisheye images on a sunny day, or near a strong light source, presents another unique challenge. It's harder to keep the strong light from causing flares in the lens, as happens when you aim a rectilinear lens at the sun. Again, experimentation will help you determine how to adjust exposure to compensate for this issue; you may even find that it adds a dramatic element to the image you're trying to capture [source: Dargaud].
Once you have the photo, you'll have to consider another signature characteristic of the fisheye lens: Even though your camera uses a rectangular sensor or piece of film, the image will come out as a circle. Remember, you're seeing the rays of light that were funneled into the lens rather than those captured straight-on by a rectilinear lens. You may decide to crop your image to a rectangle or square, or could keep it spherical to preserve the full effect of the heavy distortion around its rim. Either way, your artistic sensibility and vision will be the guide for how to best present the final images.
While considering your final presentation, it's worth it to note that the digital editing that can turn a rectilinear lens into a fisheye-esque shot can work in the other direction as well. Most photo editors include some type of straightening filter, which identifies distorted straight lines and flattens them. While the end result will still have more distortion than an image shot with a rectilinear lens, it will showcase the ultra-wide angle of view that gives the fisheye lens a guaranteed place in the gear bags of many photographers.