A mirror box is the compartment within a camera that houses one or more mirrors, typically angled to direct light from the lens to the viewfinder. In single-lens reflex (SLR) cameras, the mirror box plays a crucial role by reflecting the image up into the viewfinder, allowing photographers to see exactly what the lens sees before capturing the photo.
The design and alignment of the mirror box are essential for accurate framing and focus. Properly functioning mirror boxes ensure that the viewfinder image corresponds precisely to the captured image, making them a key component in both film and digital SLR photography.