Wild M20 microscope model H phototube. The Phototube H has a fixed beam-splitter prism which passes in to the binocular 25% of the light received; the remaining 75% goes to the camera. It is used for a vertical photomicrography, cinemicrography and television microscopy. When installed it provides a 1.25X image magnification factor. As can be seen in the last photograph, there is some separation in the diverting prism, it does not however, impinge on the light path to the camera.  Thanks for looking!