sentences:  In 1966 in response to the trend Carl Zeiss displayed a prop lens christened the Super-Q-Gigantar 40mm 0.33 at photokina.Made from various parts found around the factory (the lenses came from a darkroom condenser enlarger), the claimed speed and focal lengths were purely nominal and it wasn't usable for photography.Theoretically, the smallest f-number is 0 (or numerical aperture of 1), corresponding to a lens with an infinite exit pupil diameter.