Given a NIKON 14mm f/2.8D ED AF Ultra Wide-Angle Nikkor Lens on a full-frame sensor, in theory the field of view is HFOV: 104° x VFOV: 81°. However this lens exhibits noticeable barrel distortion increasing with the distance from the image center.
Is the lens distortion used to achieve the FOV of a perfectly rectilinear 14mm lens, meaning that the real focal length is slightly longer (i.e ~16mm Lens + Barrel Distortion = 14mm rectilinear lens) or distortion is not accounted in the computation and in practice the actual FOV is bigger then HFOV: 104° x VFOV: 81° (i.e 14mm Lens + Barrel Distortion = 12mm rectilinear lens)?
Surprisingly many websites and research papers on the topic explain lens distortion as either purposely built on fish-eye lenses or to be found only in cheap lenses due to construction errors such as misalignment. I don't think NIKON 14mm f/2.8D ED AF Ultra Wide-Angle Nikkor belongs to either of those groups.