Leica Screw Mount (LTM) Cameras

Every Leica from the original 1925 Leica I through to 1957 used the same lens attachment: a 39mm diameter thread, 26 turns per inch, that let a lens be screwed directly into the camera body. Collectors now call it LTM — "Leica Thread Mount" (or L39) — to distinguish it from the bayonet M-mount that replaced it. Over three decades the screw-mount body was refined repeatedly without ever changing that fundamental connection, which is why lenses from 1930 still fit cameras built twenty years later.

The design's most significant early upgrade came with the Leica II in 1932, which added a coupled rangefinder — a second window that let the photographer focus precisely by aligning two overlapping images, rather than guessing distance. The Leica III followed in 1933 with a separate dial for slow shutter speeds. From there, Leitz iterated steadily: letter suffixes (a, b, c, d, f, g) each marking a refinement, right up to the Leica IIIg of 1957, the last and most developed screw-mount body, built alongside the newer M3 for a further two years before the line was finally retired.