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.