 This shutter operates close to the film plane and employs metal plates or cloth curtains with an opening that passes across the light-sensitive surface.The curtains or plates have an opening that is pulled across the film plane during an exposure.The focal-plane shutter is typically used in single-lens reflex (SLR) cameras, since covering the film rather than blocking the light passing through the lens allows the photographer to view through the image through the lens at all times "except" during the exposure itself.