Anamorphic lenses are used to squeeze an image in widescreen cinematography or unsqueeze the image for widescreen projection. Usually the image is squeezed horizontally during photography and unsqueezed horizontally during projection. The most recognized tradename for this process is Cinemascope®.
Anamorphic lenses are constructed using clyindrically shaped lenses, instead of the spherically shaped lenses used in conventional lenses.
While technically an anamorphic can be made to have more or less "squeeze," the most common "squeeze factor" is 2x, which is the factor used by the Cinemascope ® process.