|Image by kind permission of Dan Lindsay - firstname.lastname@example.org|
Fisheye lenses are available in various focal lengths, ranging from about 16mm down to 6mm. A lens with a focal length of 16mm may be described as rectilinear because it is capable of producing images that have little or no barrel or pincushion distortion. In other words, objects featuring straight lines, such as utility poles or houses, can be rendered straight in the images produced. A Nikon 16mm rectilinear fisheye lens, for example, also produces rectangular images. However, lenses of shorter focal length generally produce circular images such as the one shown on the left, which shows the cathedral in Nancy, France..
Ultra-wide angle lenses can be used for producing spherical panoramas. An 8mm lens may have a 180 degree field of view, so it is necessary to take only three images in a row to complete a panorama. This is arguably the easiest approach.
Not many manufacturers produce lenses with a field of view of 180 degrees. However there are quite a few examples available on the new and second-hand markets. Some are intended only for the amateur market and are of relatively poor optical quality. Others, such as the Nikon 8mm fisheye, are of very high quality but also very expensive to buy. The Nikon lens is typically priced at around £800 in the UK.
The protruding convex surface of the front element of a typical fisheye lens make it particularly vulnerable to damage. Great care must be taken not to mark the surface of the lens because in many cases the damage will appear in focus in every image.