A diaphragm or an opaque barrier of some kind with an opening of appropriate size is useful in x-ray treatment by limiting the application to the desired region, while protecting other parts of the patient and also the operator from the influence of the rays. Its value in radiography depends not only on the above factors, but also on its exclusion of vagabond rays arising from various parts of the x-ray tube and bluring the clean-cut shadows which would be produced by the direct rays emanating fromthe focus point on the anticathode. An example of blurring, due to light radiating from a large area instead of from a single point, is seen if the fingers are held against a piece of paper a few feet from a window.
TOUSEY S. A FLEXIBLE CONTACT DIAPHRAGM AND PROTECTIVE SHIELD FOR X-RAY TUBES. JAMA. 1910;55(6):499-500. doi:10.1001/jama.1910.04330060051015