In non-reflex cameras, the shutter rotates (or opens and closes) parallel to the film, meaning it cannot reflect the image for viewing. As a result, the only way to set the focus is by measuring the distance from the object to the film surface and adjusting this distance on the camera lens. However, this method relies on having a well-calibrated lens to ensure accuracy. Some older 16 mm cameras, like Bolex Reflex and Pathé models, share similar shutter construction with non-reflex cameras. These are not mirror-reflex cameras but rather prism-based (like the Bolex) or plate- based (like Pathé) reflex cameras. In the Bolex, for instance, a prism located in front of the shutter reflects about 20% of incoming light to the optical viewfinder, allowing 80% to reach the film. The image shows the light path in the Bolex H16, which is identical to the H8 model. (Image source: Vásárhelyi István, A keskenyfilmezés, Műszaki Könyvkiadó Budapest, 1965) Element 'B' is the light-dividing prism that directs 80% of the light to the film ('A') and reflects 20% to the matte lens ('C'), which then transmits it to the viewfinder. The advantage of this design is that it provides a non-flickering image during shooting. However, the major drawback is a darker viewfinder image (only 20% of the light passing through the lens is visible), making focusing more challenging and requiring the eye to adjust to the dimness during filming – an uncomfortable situation for the operator. 43