This adapter is for CS-mount cameras to fit a C-mount Lens. C-mount lenses require about 17.5 mm to focus on the imaging device, usually a CCD or CMOS chip. C-mount lenses have a 5 mm longer flange back or focus point into the body of the camera. This adapter moves the lens about 5 millimeters away from the chip, making room for the greater distance needed for the C-mount lens focus point. CS-mount lenses cannot be used on C-mount cameras.