Pechan prisms are often utilized at the Pantex firing site to rotate a test part image for proper alignment to the streak camera slit plate. Modification of a prism mounting system provides means for the mutual adjustment of the prism axis, prism mounting axis, and streak camera optical axis. This reduces, or eliminates, image translation during rotation about the optical axis. Alignment errors, modification devices, and alignment procedures are presented for the rotational prisms employed at the test site.