A high-definition camera is installed on the wall one meter high. Can you read the text message clearly?

The high-definition camera is very close to the mobile phone, so you can see the content of the short message clearly within the focused depth of field. When the height of the wall is more than one meter, it is basically impossible to read the message clearly. At this time, the angle of view of the ordinary camera on the screen of the mobile phone is very small, and the words taken are also very small on the screen, so it is difficult to distinguish clearly even if the image is enlarged. If the camera has a large focal length and a small lens angle, the picture of the short message will be large, and the text of the short message can still be seen clearly. So we can be optimistic that the focal length of the camera is very large, or the telephoto end of the zoom camera is very large.