Normal Lens Information - Kari

In photography and cinematography, a normal lens is a lens that reproduces a field of view that generally looks "natural" to a human observer under normal viewing conditions, as compared with lenses with longer or shorter focal lengths which produce an expanded or contracted field of view that distorts the perspective when viewed from a normal viewing distance. Lenses of shorter focal length are called wide-angle lenses, while longer-focal-length lenses are referred to as long-focus lenses^[3] (with the most common of that type being the telephoto lenses).

For still photography, a lens with a focal length about equal to the diagonal size of the film or sensor format is considered to be a normal lens; its angle of view is similar to the angle subtended by a large-enough print viewed at a typical viewing distance equal to the print diagonal;^[2] this angle of view is about 53° diagonally. For cinematography, where the image is normally viewed at a greater distance, a lens with a focal length of roughly double the film or sensor diagonal is considered 'normal'.

The term normal lens can also be used as a synonym for rectilinear lens. This is a completely different use of the term.


http://en.wikipedia.org/wiki/Normal_lens