The intensity distribution and dimensions of the x‐ray tube focus can be recorded accurately and rapidly by scanning with a pair of molybdenum rod slits and a scintillation counter. Two methods were used: (1) the image‐forming slit mounted near the x‐ray tube remains fixed and the image is scanned with another slit mounted on the detector; (2) both slits and detector are translated as a unit across the focus. The vignetting was analyzed and can be made negligible in both methods. Magnification of the image is not possible with method (2), but it has the advantage of minimum vignetting and easier alignment.