What device attached under the tube housing helps vary the size of the radiation field?

The collimator is an essential device used in radiography to control the size and shape of the radiation beam emitted from the X-ray tube. This device plays a crucial role in ensuring that only the necessary area is exposed to radiation, which mitigates the risk of unnecessary exposure to surrounding tissues and helps to improve the quality of the radiographic image. By adjusting the collimator, operators can focus the beam to match the anatomical area being examined, thereby enhancing image clarity and minimizing scatter radiation.

Utilizing a collimator not only maximizes the efficiency of each exposure but also adheres to radiation safety principles, as it limits the patient's radiation dose and reduces the amount of scatter that potentially affects imaging quality. This device serves as a fundamental aspect of radiographic practice, ensuring accurate and safe imaging.