What's the best shade number for welding glass attached to a webcam which is used to record images of the Sun?

Hi, I am trying to use a webcam (Logitech Quickcam Express) to take pictures of the Sun throughout the day for one of the projects I am working on. In order to protect the camera lens from being burnt by the direct sunlight, I think it might be a good idea to place a piece of welding glass in front of the camera. However, I need to determine the optimal shade number of the welding glass for my particular application. Does anyone know what shade number(s) I should choose? Thanks.