Fisheye

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A fisheye lens is a special wide-angle lens which is not corrected for linear distortion, and is able to show 180˚ angle of view.

There are two types of fisheye lens.

• Circular fisheye, which creates a circular image on the sensor which is 180˚ across in all directions.
• Full-frame fisheye, which fills the frame, giving 180˚ across the diagonals. These are generally considered to be the most useful.

All lines passing through the centre of the lens suffer no linear distortion. Lines which do not pass through the centre suffer progressively greater distortion, until the point that, at 90˚ from the lens centre, they are fully circular.

In many circumstances, a fisheye lens can be used as an extreme wide angle, if the only straight lines in the image are placed in the centre. Most viewers will not be aware of the progressive distortion of the rest of the image.

Fisheye lenses do not suffer the vertigo-inducing perspective distortion of super-wide angle lenses. However, they do tend to suffer from chromatic aberration, despite heavy correction.

Fisheye images can be 'straightened' in Nikon Capture NX and through Panotools, among others. This does not necessarily produce a less distorted picture, because the barrel distortion of the fisheye is replaced with the extreme perspective distortion of the super-wide angle. Furthermore, a substantial amount of quality is lost.