Other factors being equal, the integrated intensity of a powder diffraction reflection is a function of the geometry of the source, collimator, and sample. By means of a geometrical and algebraic analysis one can predict the relative intensities to be expected with pinhole or slit collimators of different dimensions. Important gains in intensity can be obtained by replacing pinholes with slits, and the advantage is about the same if the x‐ray focal spot is viewed either longitudinally or laterally through slits of sufficient length. These results confirm experimental results reported by other investigators and also re‐emphasize the potential value of the ``side'' windows of x‐ray tubes, which are commonly neglected.