How to install the door cat's eye after it is disassembled?

1. Put the side with the glass lens outside the door.

2. Leave the other half at the door.

3. Then slowly tighten the screw by hand.

4. finally, lock.

Cat's eye, also known as door mirror, is a small optical instrument installed on the door of a house to facilitate residents to observe outdoor conditions. It has become a necessity for family safety. It consists of a concave lens (objective lens) and a convex lens. The focal length of the objective lens is extremely short, which makes people or things outdoors become upright and narrow virtual images, and this virtual image just falls within the focal range of the eyepiece, and finally an enlarged upright virtual image is obtained, which is just near the visual distance of human eyes, so that the situation outside the door can be clearly seen.