Lens mount

Screw-threaded mounts are fragile and do not align the lens in a reliable rotational position, yet types such as the C-mount interface are still widely in use for other applications like video cameras and optical instrumentation.

Lens mounts of competing manufacturers (Sony, Nikon, Canon, Contax/Yashica, Pentax, etc.)

In addition to the mechanical and electrical interface variations, the flange focal distance from the lens mount to the film or sensor can also be different.

For small camera modules, used in e.g. CCTV systems and machine vision, a range of metric thread mounts exists.

Various lensmakers also offer optical accessories that mount in front of the lens; these may include wide-angle, telephoto, fisheye, and close-up or macro adapters.

This has the side effect of decreasing the amount of light that reaches the sensor, as well as adding a crop factor to the lens.

Without the secondary lens, these adapters will function as an extension tube and will not be able to focus to infinity.