For the average beginner photographer, a basic and inexpensive fisheye lens will do quite nicely, as it provides the fishbowl scenes that are reminiscent of the first fish eye lenses. However, with advancements in photography, cameras and lenses, you no longer have to put up with distorted fisheye pictures that literally look like they were taken from inside a fishbowl. Knowing how to choose a fisheye lens, what you expect from it, as well as your cost limitations will enable you to get the best deal possible on a fisheye lens for your specific purposes.
When shopping for a fish eye lens for your single frame reflex (SLR), or digital SLR camera, cost is usually the main factor in choosing which fisheye lens you purchase. In order to get a fully 180 degrees of portraiture without any physical distortion, a costly (over $600), 10.5 mm fisheye lens is needed, or, at the very least, extremely wanted. Added software for your digital camera needs to be installed to use this lens properly, but no distortions or stretched people or objects ruin the shot. What you get is a realistic, 180 degree view of your subject.
With the more expensive fisheye lenses, you get a more complete package in fisheye lens use. You can take close-up pictures, as close as one an a quarter inches, or 3.2cm from the object you are taking a picture of with little to no distortion to the close-up objects. Even at ten feet from the subject, a 35mm fisheye lens will give major distortion, and make the scene appear to be shot from inside a fish bowl, not from the perspective of a 180° view.
For more inexpensive tastes and budgets, and if you have a 35mm camera, the 35mm fisheye lenses are more your cup of tea. 16mm auto-focus (AF) fisheye lenses will give the best view with the least amount of distortion for 35mm film cameras, but will cost significantly more than the 35mm fisheye lens. Consider buying your fisheye lens from the many used camera and camera supply stores, as well as from online forums and stores.
One final piece of advice for purchasing fisheye lenses is that sticking to the brand of camera that you have when buying lenses is not necessarily the best avenue to follow. Many after-market lenses are mush better than their namesakes, and offer a better, leww distorted picture.
Shop safe. Shop informed.