Smearing effects in `pinhole' collimation with one-dimensional detection

Owing to the recent availability of intense X-ray sources, small-angle X-ray scattering experiments can now be performed with pseudo-pinhole collimation. However, smearing effects are still present in `pinhole' data collected with one-dimensional detectors, owing to both the finite size of the beam and particularly the finite width of the detector window or mask. The smearing effects are shown to be severe at very low scattering vectors, leading to grossly incorrect values of the correlation lengths determined for samples with a random two-phase morphology. Though the degree of smearing induced by `pinhole' collimation is smaller than that from slit collimation, the effect on the correlation lengths determined from the smeared data is similar in magnitude for common camera parameters. With simulated data and incorporation of both random noise and a truncated q range, it is shown that data can be desmeared using the iterative method of Lake [Acta Cryst. (1967), 23, 191-194] to yield reasonable values of the correlation length.