The beam ratio (reference beam intensity to object beam intensity) which produces maximum contrast photographic reconstructions from double-exposure holographic interferograms was experimentally determined to be 1.2 ± 0.2.
J. E. Sollid and J. B. Swint, "A Determination of the Optimum Beam Ratio to Produce Maximum Contrast Photographic Reconstructions from Double-Exposure Holographic Interferograms," Appl. Opt. 9, 2717-2719 (1970)