The terms Fast or Slow Lens refers to the maximum aperture of a lens. A Fast lens allows a great deal of light to be transmitted, whereas a slow lens lets very little light in. Maximum apertures are referenced as ‘f-stops numbers’, with the smaller f-stop representing a fast lens (cinematography)
FAST is a term well understood by camera crew in the film and video production industry. It means that the camera assistant must check Focus, Aperture, Shutter and Tachometer. (Camera crew)