SLR cameras can't focus automatically. What happened?

The following problems will cause the SLR to fail to focus automatically. Please check them one by one. \x0d\ 1。 The focal length exceeds the nearest focal length of the lens. \x0d\2。 The camera is set to MF manual focusing mode. \x0d\3。 The lens is set to MF manual focusing mode. \ 4. The telephoto lens did not choose a good focus, which led to the bellows being pulled. \ x0d。 5. There is no obvious light-dark boundary near the focus, which leads to the inability to focus \x0d\6. The light is too weak to focus \x0d\ If you can't focus after the above points are completed, it may be \x0d\ 1. The focus screen is shifted, which makes it impossible to focus \x0d\2. There is dust on the focus screen x0d \ 3.