it is a cylindrical lens using all frame area and compressing horizontal field in order to obtain wide field coverage at horizontal plane and normal wide angle at vertical planes. It is called also "squeezing" or "slimming" lens . The projection through a similar lens recomposes the image as we see it normally. Regards LP
Wikipedia says: CinemaScope is an anamorphic lens series used, from 1953 to 1967, and less often later, for shooting widescreen films that, crucially, could be screened in theatres using existing equipment, albeit with a lens adapter. Regards, Detlev