Cameras and lens can be either C or CS mount. Most cameras today are CS mount. Using a C mount lens on a CS mount camera will require using a C mount adapter which is a 5mm spacer. Most lens and/or camera manufacturers provide this type of adapter. Mis-matching the lens, camera and adapter will make it impossible to focus a lens. To achieve the best focus; focus the lens as best as possible. Then use the camera's flange back adjustment. In most cases changing the camera's flange back adjustment will require loosening a locking screw. After the adjustment is made, make certain the locking screw is tightened.