In this paper, a comparative experimental study on optical transparency of z-cut LiF, sapphire and LiTaO3 under 1011 Pa shock compression at our two-stage light-gas gun facility is presented. In our experiments, intensity contrast variation of light emitted from a modified experimental setup of Mallory-type was monitored by a high-speed electronic camera. The results demonstrated that the LiF under the shock pressure of 102 GPa retains its initial transparency in the whole observation time interval, which is in good agreement with the common view of good sustained transparency of LiF. The LiTaO3 became basically opaque at 139 GPa. Sapphire at 131 GPa shock pressure showed a continuous transparency degradation till became completely darkened when the shock wave was arriving at the free-surface.