I don't know which kind of camera you are using, but with both Point & Shoot, and SLR, If you manage to block part of the lens it means that you are not holding your camera in a proper and stable way. With Point and Shoot you should hold the camera with both hands and support the camera from the sides. If you are using SLR the right hand is busy with pushing the button, while the left hand should support the camera by holding it under the lens, and controlling the zoom and manual focus.