Monorail cameras are view cameras with lens mount, bellows, and interchangeable viewing and film backs all fitted along a rigid rail along which they can slide until locked into position. They can take sheet film in large sizes, and since the advent of digital photography can take a digital back. They are used to take very high-quality photographs of static subjects on large film, or at high digital image resolution, and capable of much enlargement with good quality. They have many camera movements for image control. The image is usually viewed on a ground-glass screen in the film plane; after the scene has been composed, the ground glass is replaced by the film, and the exposure made. Monorail cameras rarely have any other viewfinder than the ground glass. Details Virtually any lens can be fitted, and backs for sheet film, rollfilm, digital back and Polaroid backs. For some uses with long exposures, or flash lighting; a shutter is unnecessary; removing a lens cap to expose the film is sufficient. Extremely small apertures such as 64 can be used without issues of diffraction on the lenses, of much larger focal length than those used for smaller images (a small relative aperture is still a fairly large hole, reducing diffraction). The trade-off for their versatility is their large weight and bulk, and use limited to slow photographs of static subjects. Some models, such as the Arca Swiss F-Line, are more compact and designed for field use, still retaining generous movements; however the F-Line cameras still weigh about 3 kg. Monorail cameras have capabilities that most other cameras do not. Both the lens and the film planes are separate and can be moved independently. By moving the front of the camera, the lens plane, independently of the rear which houses the film, the photographer can alter the depth-of-field (actually, the plane of sharp focus) without changing the perspective of the image. The converse is also true. The rear of the camera, which holds the film, can be moved to alter or improve the perspective of the image without changing the depth-of-field. Film is typically loaded one sheet at a time into a special holder. Each film holder can hold two sheets of film - one on each side of the holder. Different holders can be loaded with different film; the type of film can be changed from one photograph to the next. Typical