Subminiature cameras are usually defined as any still camera that exclusively uses a single film format smaller than 16.7mm x 30.2mm, which is the size of the Advanced Photo System's (APS) IX240 film. The size of the camera is not the determining factor, though in most cases these cameras are some of the smallest ever produced. There are a variety of contemporary and historical subminiature formats, including (but not limited to) Minox, 16mm, disc, and half-frame cameras. The majority of these cameras are not toys. In fact, many of them have some of the more advanced optics of their time, as well as being mechanical marvels. Many older models rival the better lenses produced today. Cameras produced fifty years ago are carried daily in the pockets of many professional photographers.