For stars fainter than Mv ≈ 6 the density distribution perpendicular to the Galactic midplane can be approximated by an exponential fall-off with a scale height of about 270 pc. We show that even if in fact constant an apparent decrease of the scale height to about 150 pc for stars with Mv ≈ 17 can be expected if all ‘stars’ measured in the photographic surveys are unresolved binaries. In principle measurements of the apparent scale-height allow the study of the mass-ratio distribution and the proportion among ‘stars’ of binary systems.