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
Less-than sign encoded as a single-byte code point token. In Fortran, operator .LE. means "less than or equal to". In Bourne shell and Windows PowerShell, the operator -le means "less than or equal to". In the R programming language, the less-than sign is used in conjunction with a hyphen-minus to create an arrow (codice_1), this can be used as the left assignment operator. In Bourne shell (and many other shells), less-than sign is used to redirect input from a file. Less-than plus ampersand (<&) is used to redirect from a file descriptor. Less-than sign is used in the spaceship operator. In HTML