A fish-eye lens is an ultra wide-angle lens that provides an extremely broad field of view of up to 180 degrees or more, encompassing virtually everything in front of the camera within a single frame. Unlike conventional wide-angle lenses, which are optically corrected to render straight lines as straight in the final image, fish-eye lenses are deliberately left uncorrected for curvilinear distortion, producing the characteristic sweeping, spherical perspective that gives the lens its name.
Fish-eye lenses are available in two principal types. A circular fish-eye lens produces a complete 180 degree hemispherical image that appears as a round circle in the centre of the frame, surrounded by unexposed black borders. A full-frame fish-eye lens, by contrast, is designed so that the distorted image fills the entire rectangular frame of the film or sensor, cropping the circular projection to produce an image that covers the full picture area while retaining the dramatic barrel distortion and exaggerated perspective characteristic of the fish-eye effect.
The extreme distortion produced by a fish-eye lens causes straight lines that do not pass through the very centre of the frame to appear as pronounced curves, bending outward towards the edges of the image in a way that creates a distinctive and immediately recognisable visual effect. Horizontal and vertical lines at the periphery of the frame can appear dramatically bowed, while subjects close to the lens appear greatly exaggerated in size relative to those further away, producing a strong sense of depth and spatial distortion.
Fish-eye lenses have a wide range of practical and creative applications. They are used in architectural and interior photography to capture entire rooms or spaces in a single shot, in sports and action photography to place the viewer dramatically close to the action, and in scientific and technical photography for applications such as sky surveys and hemispherical imaging. In creative and artistic photography, the fish-eye's unique perspective and bold distortion are exploited to produce striking, unconventional imagery that would be impossible to achieve with a conventional lens.