This adapter is a CS Lens adapter for the QHY5 series of camera. The back focus to the CCD plane is 12.5mm with this adapter, otherwise the C mount has 17mm. This will enable the camera to be attached to the QSI OAG cameras. There is no glass in this adpater. which will work fine for Mono cameras. If you are using color you need to add an IR filter to get true color.