Depending on the rotation angle of the prism and the incident surface of the light, the Dowie prism can make the image rotate, stand upside down or reflect back. In a Dowie prism, light usually travels along the longitudinal axis of the prism. Light is reflected once on the bottom surface, forming an inverted image on the other side of the prism. Rotating the prism along the longitudinal axis causes the image to rotate at twice the speed of the prism. Because of the large incident angle, the light is totally reflected at the bottom of the prism, even if the propagation axis of the light is not completely parallel to the longitudinal axis of the prism. Therefore, the internal transmittance of Dowie prism is only limited by the absorption rate of prism.
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