50% of the time; Film records the image when stationary in the camera. Almost all movie cameras use half the time replacing the last film 'frame' with a new one: '180degrees' of the shutter cycle. Thus, if you film a Dolphin jumping, he is recorded as a broken series of blurred stills ('trails'). A 48th of a second is missing during frame replacement, a 48th of a second is recorded, but his movement smears the image. Humans see this flicker, so film projectors break each cycle into 3 flickers....

Sorry, to many words.......... Take your five year old to see the film 'Gandhi', the flicker and strobeing is unbearable.