Because of the weakness of diffracted beams, it is necessary to work in the low gradient ``toe'' portion of the characteristic (D‐logE) curve. The curve shape in this region is the same for all types of x‐ray film commonly used, even when development is greatly prolonged.The shape of the entire characteristic curve is insensitive to radiation quality, but the relative speeds of different films change considerably in the range of wavelengths of interest to diffractionists.For photographic photometry, the linear density‐exposure range can be extended by proper selection of the processing conditions.