We evaluated the relation between the degradation of the Bragg selectivity and the optical densities of the films by use of the shift-multiplexing method with a spherical reference wave. Our recording media were prepared by blending methylazobenzene-containing polymer (MAP) and cyanobiphenyl-containing polymer (CBP). We fabricated four kinds of 250μm-thick films whose optical densities were increased with MAP concentrations that ranged from 10wt% to 70wt%. As a result of the evaluation, the film with a higher optical density degraded the Bragg selectivity more significantly. The degradation of the Bragg selectivity affected the bit error rate (BER). In addition, we obtained a guide to holographic recording conditions for achieving a low BER as to the films with non-negligible optical densities.