What covers the lens in front of the camera?

Removable lenses? If it is rotatably mounted on the outermost layer of the lens, it should be a uv lens, whose basic function is to protect the lens. The other is placed in front of the lens through a special bracket or slot, which is called a filter. There are many kinds, such as gray film, color filter, gradient mirror and so on. Which one is specific can be judged according to the installation method.