Fisheye Lens
An ultra-wide lens that deliberately abandons rectilinear projection, bending straight lines to squeeze 180° or more into the frame.
Formula / rule
r = f × θ (equidistant)
Measured in
mm
In depth
Conventional wide lenses keep straight lines straight, which forces extreme stretching at the edges; a fisheye accepts curvature instead and so packs in far more scene with less corner smearing. Circular fisheyes project a disc inside the frame, while full-frame fisheyes fill it. The distortion can be mapped back to rectilinear in software, at the cost of edge resolution.
Examples in practice
An 8 mm circular fisheye captures the entire sky in one frame for a cloud study or a virtual-reality panorama.