Historic Lens Mounts
The physical interface between camera body and optics is a study in precision engineering. We document flange focal distances and mechanical linkages.
| Mount Name | Type | Flange Distance | Notable Linkages |
|---|---|---|---|
| M39 / LTM | Screw Thread | 28.80 mm | Rangefinder coupling cam |
| M-Mount | Bayonet | 27.80 mm | Frameline selector lug, RF cam |
| F-Mount (Pre-Ai) | Bayonet | 46.50 mm | Meter coupling "rabbit ears" |
| OM-Mount | Bayonet | 46.00 mm | Aperture stop-down lever, depth-of-field preview |
| M42 | Screw Thread | 45.46 mm | Auto-aperture push pin |
Mechanical Data Transfer
Before electronic contacts, cameras relied entirely on mechanical linkages to transmit data between the lens and the body light meter. For example, early Nikon F-mount lenses utilized external metal prongs (colloquially called "rabbit ears") that physically hooked onto a pin on the camera's photomic prism to index the maximum aperture.
The transition from screw mounts (like M42 and M39) to bayonet mounts was driven by the need for faster lens changes and more precise rotational alignment, ensuring that internal aperture levers aligned perfectly every time.