CS / C-Mount Extension Ring for Industrial & CCD Cameras — Focus Adjustment Adapter Tube, 0.5mm–20mm

The correct thickness depends on the back focal distance (BFD) mismatch between your lens and camera sensor. Calculate the difference between your lens's designed flange focal distance and your camera's actual back focal distance. Select the ring thickness that closes this gap. For fine-tuning, thinner rings (0.5mm, 1mm, 2mm) are generally used; for larger corrections, 5mm, 10mm, 15mm, or 20mm rings are more appropriate. Rings can also be stacked to achieve intermediate values.

CS-mount extension rings are designed for CS-mount cameras and lenses, which have a flange focal distance of 12.526mm. C-mount extension rings are designed for C-mount systems, which have a flange focal distance of 17.526mm. Both use the same 1″ × 32 TPI thread standard. The most common use of a C-mount extension ring is the standard CS-to-C conversion: a 5mm C-mount ring allows a C-mount lens to be used on a CS-mount camera with correct back focal distance.

All rings share an outer diameter of 30mm (≈1.18") and an inner clear aperture of 25mm (≈0.98"). CS-mount threaded variants have an inner thread diameter of approximately 22.5mm. The thin shim-style rings (0.5mm, 1mm, 2mm) have an inner diameter of approximately 25.5mm and no threads — they act as precision spacers between the lens and camera body. Manufacturing tolerance is approximately ±1–2mm.

Yes. Extension rings can generally be stacked to achieve a combined thickness. For example, a 5mm ring and a 10mm ring can be combined to achieve 15mm of total extension. However, each additional ring introduces a small amount of mechanical tolerance, so using a single ring of the correct thickness is generally preferable when available to maintain the best optical axis alignment.

These rings are machined from aluminum alloy with an anodized black finish, which provides good resistance to light corrosion and humidity for typical indoor industrial use. They are not sealed or rated for outdoor weatherproof applications. For harsh outdoor or high-humidity environments, additional sealing of the camera housing is generally recommended.

Both CS-mount and C-mount lenses use the same 1″ × 32 TPI (threads per inch) thread standard. The difference is not the thread size but the flange focal distance: CS-mount is 12.526mm and C-mount is 17.526mm. A C-mount lens can be used on a CS-mount camera with a 5mm extension ring, but a CS-mount lens cannot be used on a C-mount camera without moving the sensor closer to the lens — which is generally not possible.

These extension rings are compatible with any industrial or machine vision camera that uses a standard CS-mount or C-mount interface, including cameras from Hikvision, Basler, FLIR, Allied Vision, IDS, Daheng Imaging, MindVision, and most other industrial camera manufacturers. Compatibility depends on the mount type — verify whether your camera uses CS-mount or C-mount before selecting a variant.