Final answer:
The radiographer adjusts the controls on the collimator to determine the size of the x-ray field, including the length and width.
Step-by-step explanation:
The radiographer determines the size of the x-ray field by adjusting two controls on the collimator, one for the length and one for the width of the x-ray field. By adjusting these controls, the radiographer can ensure that only the desired area is exposed to radiation, while limiting exposure to other tissues.