This type of camera was first developed in the era of the daguerreotype (1840s-1850s) and is still in use today, some with various drive mechanisms for movements (rather than loosen-move-tighten), more scale markings, and/or more spirit levels. It comprises a flexible bellows that forms a light-tight seal between two adjustable "standards", one of which holds a lens, and the other a ground glass or a photographic film holder or a digital back. There are three general types, the rail camera, the field camera, and others that don't fit into either category.