What is the principle of the security Door viewer?

- Mar 22, 2019-


The security door cat eye is composed of a concave lens (objective lens) and a convex lens. The focal length of the objective lens is extremely short, which makes the outdoor person or object a virtual image that is erect and narrow. This image falls within the focus of the eyepiece, and finally a reduced erect virtual image is obtained. This image is just in the human eye. Nearby, the situation outside the door can be seen clearly.


When we look out from inside the door, the objective lens L1 is a concave lens and the eyepiece L2 is a convex lens. The focal length of the objective lens L1 is extremely short, and it makes the outdoor person or object AB a small erect virtual image A'B', which falls within the first focus of the eyepiece L2, and L2 acts as a magnifying glass. Finally, a more enlarged erect virtual image A〃B〃 is obtained. This image is just near the bright distance of the human eye. For the situation outside the door, it can be seen clearly.




What is the role of the security door cat eye?

Looking out from the room through the door mirror, you can see all the scenes in the range of about 120 degrees outside the door, but you can't see anything in the room through the door mirror. If you install this mirror on the door of a public house or private apartment, it can play a certain role in the anti-theft and security of the family.


The anti-theft door cat eye is generally installed on the anti-theft door of the home. When someone knocks on the door, the person in the house can see the situation outside the door through the cat's eye. It is very clear when looking through the cat's eye from the house, and when you look at the house from outside the house, It became very blurred. Therefore, the importance of home security is of great significance. In addition, the cat's eyes are exquisite and beautiful, and have a decorative function.