Of greater importance is the next model, introduced in 1930 that offered interchangeable lenses. Still called Leica I (but Leica C in America), the camera accepted lenses with focal lengths of 35, 50 and 135mm with apertures of respectively 3.5, 3.5 and 4.5. Every lens had to be individually adjusted on the body, a rather awkward procedure. (the lenses adjusted to a certain body received the last five (later last three) digits of the serial number of that body). A year later (1931) the company switched to standardized mounts (the camera name did not change) and introduced in addition: the 4/90, 1.9/73 and 2.5/50. This range of 35-50-73 (75)-90-135 became the classical range for decades to come.