An anamorphic lens is designed with additional glass elements that squeeze the image horizontally, allowing filmmakers to capture a wider field of view than the film or digital sensor would ordinarily allow.
In production there are typically two classes of lenses — anamorphic and spherical. Spherical lenses are the most common and project images onto a camera’s film or digital sensor without affecting their aspect ratio.
Anamorphic lenses expand the frame horizontally, accommodate more shooting width, and can output shots with a wide-format specification ratio without cropping. This has a significant advantage in film. It allows filmmakers to achieve wide aspect ratios without sacrificing resolution via cropping, which would typically have to be done when using a spherical lens to achieve widescreen aspect ratios.
Anamorphic lenses also have distinct features which provide a unique look on screen. These include oval bokeh, light flares, greater depth of field and the widescreen ratio.