Types of Camera Lens Mounts – C-Mount, CS-Mount, and M12 Mount (S-Mount)

What is the difference between C and CS mount?

C-Mount vs CS-Mount Lenses

C-mount and CS-mount are both common screw-threaded lens mounts used in machine vision and CCTV cameras. They share the same thread size (1-inch diameter, 32 threads per inch), but the flange height (also known as focal distance FFD) is different. The flange focal distance is the distance from the mount’s shoulder to the camera’s image sensor plane. 

We believe the "S" in CS-mount means "Short" which explains why:
- C-mount lenses have a standard flange height of 17.526mm.
- CS-mount lenses have a 5mm shorter FFD of 12.5mm. This improves optical performance and/or reduces optical design complexity and cost.

C-mount vs CS-mount compatibility is therefore one-way: 

1.) A C-mount lens can only reach focus on a CS-mount camera if a 5mm spacer ring is added.

2.) CS-mount lenses CANNOT be used on C-mount cameras. Physically the lens will thread on, but because the CS lens is designed for a shorter distance, it will focus the image in front of the sensor on a C camera. There is no simple adapter to fix this – the lens just can’t be placed far enough forward to focus on the sensor.

M12 Lens Mount vs C-Mount vs CS-Mount Lenses

M12 lenses (also known as S-mount lenses) are miniature lenses with a 12 mm diameter thread (M12 x 0.5). They are widely used in compact board cameras.

Comparing an M12 lens vs a C-mount lens (or CS-mount) reveals major differences in size and standardization: 

Physical Size and Thread:
M12 lenses are much smaller. They use a metric M12×0.5 thread instead of the 1″-32 UN thread of C/CS mounts. The entire lens is often only a few centimeters long. This compact size makes M12 lenses ideal for small embedded cameras, but it also means they typically work with smaller image sensors up to about 2/3″ sensor formats.

In contrast, C-mount lenses are larger and can support sensors up to around 1″ or more. 

Flange Focal Distance:
Unlike C/CS, the M12 mount does not have a standardized flange focal distance. The distance from the lens to the sensor in M12 systems depends on the specific lens design and the lens holder used. Each M12 lens must be matched with a compatible lens mount holder and adjusted (typically by screwing in/out) to focus on the sensor.

Not all M12 lenses are interchangeable across different holders or cameras – you must ensure the mechanical back focal length and lens barrel length suit your camera’s mount. In other words, an M12 lens that works in one camera might not focus in another if the lens housing is different.

Mounting and Adaptability:
M12 lenses screw into small lens holders on the camera board (often secured with glue or screws once focused). These holders are sometimes called S-mount or board-mount holders. Adapters do exist to use an M12 lens on a C-mount or CS-mount camera. However, compatibility is not guaranteed.  In practice, if you attach an M12 lens with an adapter to a C-mount camera, it may not be able to focus to infinity or it might vignette since M12 lenses are designed for smaller sensors.

Always check the lens specifications and, if possible, test the combination before committing to an M12-vs-C/CS swap. In short, M12 vs C-mount/CS-mount lenses trade off flexibility for size and cost. 

A Machine Vision Camera and Lens Compatibility Table

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