CS Mount

The CS mount is a standard specification for mounting lenses to cameras, primarily utilized in the fields of closed-circuit television (CCTV), machine vision, and scientific imaging. It is a derivative of the older and widely established C mount standard, designed to accommodate smaller sensors and more compact camera designs.

Specifications

The physical thread specifications of the CS mount are identical to those of the C mount. The defining characteristic that separates the two is the flange focal distance (FFD), also known as the flange back distance. This is the distance from the mounting flange (the metal ring on the camera and lens that mate together) to the camera's image sensor.

  • Thread Diameter: 1.000 inch (25.4 mm)
  • Thread Pitch: 32 threads per inch (designated as 1-32 UN 2A)
  • Flange Focal Distance (FFD): 12.5 mm

Because the CS mount requires a shorter flange focal distance, camera bodies utilizing this standard can be manufactured to be smaller and lighter than their C mount counterparts. Furthermore, CS mount lenses can often be designed more simply and cost-effectively, particularly for wide-angle applications, because the rear element of the lens sits closer to the sensor.

Compatibility with C Mount

Because the thread diameter and pitch are identical, C mount and CS mount components can physically screw into one another. However, optical compatibility is dictated by the flange focal distance:

  • C Mount Lens on a CS Mount Camera: This combination is compatible but requires an adapter. Because the C mount lens expects a distance of 17.526 mm to focus properly, and the CS mount camera only provides 12.5 mm, a simple 5 mm spacer ring (often called a C/CS adapter) must be threaded between the lens and the camera.
  • CS Mount Lens on a C Mount Camera: This combination is generally incompatible. A CS mount lens needs to sit 12.5 mm away from the sensor. If mounted on a C mount camera (which places the lens 17.526 mm away), the lens will be positioned too far from the sensor. It will act as an extension tube, making the lens unable to focus to infinity and rendering it suitable only for extreme macro close-ups, if it focuses at all.

Applications

The CS mount was widely adopted during the transition from large vacuum tube security cameras to smaller solid-state CCD and CMOS sensors. Its primary applications include:

  • CCTV and Security Systems: It remains a dominant standard for interchangeable-lens security cameras.
  • Machine Vision: Used extensively in automated inspection, robotics, and industrial quality control systems where compact, reliable optics are required.
  • Microscopy and Scientific Imaging: Frequently used to attach digital camera bodies to the phototubes of microscopes.
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