Sometimes these lenses will not automatically focus when fully screwed into the lens holder. This is generally due to one of the problems below:
The lens format is incompatible with the image sensor format. When purchasing a C- or CS-mount lens, make sure it is compatible with the image sensor size (e.g. 1/3", 2/3", etc.) used by your camera.
The lens is a C-mount lens. If this is the case, the lens spacer can be purchased and placed between the camera and lens.