a case hinges to the side of the movie camera next to the ground glass . one end of a viewfinder tube mounts pivotally to the case ; the other supports an ocular . light from the inverted image on the ground glass passes , at a right angle to the camera side , into the case . an amici prism in the case reerects the image and reflects the light rearward to a beam splitter . the splitter passes part of the light rearward to a 45 °/ 90 ° prism and then upward through a lens and iris to a video port and neutral - density filter . the beam splitter deflects the rest of the light outward , at a right angle to the camera side , into the finder tube . there another 45 °/ 90 ° prism deflects the light rearward in the tube to a lens that reimages the scene at the ocular . the movie camera can thus be tilted while the tube and ocular are at constant height , but prism rotation twists the image about the optical path . to correct this , a pechan prism between the lens and the ocular is linked to rotate about the path when the finder tube pivots . the pechan prism counterrotates the image . in the finder are also a filter wheel and optional 2 × reducing lens .