Ultra wide angle lens the difference is only whether distortion is present or not. However, the shorter the focal length, the more difficult it is to implement rectilinear correction. In fisheye lenses, the visual angle is close to or more than 180 degrees in at least one direction. For example, a "diagonal fish eye" would have a viewing angle of at least 180 degrees within the diagonals of the frame. A "circular fisheye" would represent the image in the form of a circle. Rectilinear ultra-wide angle lenses are used in photography and cinematography sometimes to achieve three-dimensional perspective distortion instead of simply two-dimensional barrel
Mast radiator as tall as 5/8 wavelength (225 degrees) are somewhat common. Any simple radiator (or array of radiators) which is taller than 195 degrees is generally not considered to have anti-fading properties. A more complex anti-fading antenna is a vertical radiator which is sectionalized and is one wavelength (360 degrees, generally 180 over 180 degrees, and historically and correctly termed a "Franklin" radiator; two in an array at KFBK), or 300 degrees (180 over 120 degrees, and formally called a WHO radiator), or 240 degrees (120 over 120 degrees, and formally called a WOAI radiator, but WOAI has since replaced this