Lens Mounts

There are many ways to interface a lens to a camera. Lenses and cameras have several standard mount types that feature either threads or a bayonet-type mount. A lens needs to not only be mechanically compatible with the mount type; it also must have the same flange distance as the camera. Flange distance or flange focal distance is the distance from the mounting shoulder to the image plane.

C-Mount

The C-Mount standard is one of the most common lens mount types in machine vision. The C-Mount standard features a thread 1” in diameter with 32 threads per inch (TPI). The C-Mount flange distance is 17.526mm. It is ideal for many industrial applications, as the threaded mount provides a robust, controlled interface between the camera and lens.

The CS-Mount standard is the same as the C-Mount standard, but with a reduced flange distance of 12.526mm. A CS-Mount camera can be modified to accommodate C-Mount lenses with the use of a 5mm extension tube between the lens and camera. A CS-Mount lens may appear to be compatible with a C-mount camera because it will thread onto it. However, a CS-Mount lens cannot be used with a C-Mount camera because the lens will focus the image at a location inside the flange and in front of the sensor.

F-Mount

The F-Mount standard is a bayonet-style mount common with line scan cameras and large format cameras. It was developed by Nikon and is used on 35mm (43.3mm) SLR photography cameras. The F-Mount standard features a diameter of 44mm and a flange distance of 46.5mm. The spring-loaded bayonet connection provides ease of use for photographers but can contribute to camera-lens misalignment in industrial applications.

TFL & TFL-II Mount

The TFL-Mount was designed for use with APS-C (27.9mm) sensors that are much too large for use with a C-Mount, but are still too small for an F-Mount. This mount can be thought of as a larger C-Mount; it has thread dimensions of M35x0.75mm, and the same flange distance as the C-Mount: 17.526mm. The TFL-Mount provides the same robustness as the C-Mount but for larger sized sensors, without the drawbacks of the F-Mount. Similar to the TFL-Mount is the TFL-II Mount which was designed for APS-H (35mm) sensors and consists of the same 17.526mm flange distance but with M48x0.75 thread dimensions

S-Mount (M12)

The S-Mount is a common mount in surveillance CCTV cameras and board-level cameras and is used with M12 lenses. This smaller mount type has a metric thread and pitch of M12x0.5 and no standardized flange distance. 

Figure 1: A depiction of the C-Mount, F-Mount, TFL-Mount, and TFL-II Mount lens mount styles showing thread size, pitch, and flange distance.