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
Angle C, and ∠CAB to the anticlockwise (positive) angle from C to B. The names, intervals, and measured units are shown in a table below: When two straight lines intersect at a point, four angles are formed. Pairwise these angles are named according to their location relative to each other. A transversal is a line that intersects a pair of (often parallel) lines and is associated with "alternate interior angles", "corresponding angles", "interior angles", and "exterior angles". There are three special angle pairs which involve the summation of angles: The size of a geometric angle is usually characterized by the magnitude