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
Screen angle depend on how many colors are used and the preference of the press operator, typical CMYK process printing uses any of the following screen angles: Screen angle In offset printing, the screen angle is the angle at which the halftones of a separated color is made output to a lithographic film, hence, printed on final product media. In offset printing, colors are output on separate lithographic plates. Failing to use the correct set of angles to output every color may lead to a sort of optical noise called a moiré pattern which may appear as bands or waves in the