Many home security doors have cat s eyes, and when you look out through the cat s eye from the insid

Updated on Security door 2024-07-26
1 answers
  1. Anonymous users2024-01-24

    The common name of the door mirror is cat's eye. Why is it called a cat's eye? Because the light is refracted through it and looks like the light emitted by the Persian cat's eyes at night, it is nicknamed the cat's eye.

    Function: Looking out through the door mirror from the inside, you can see all the scenes within the range of about 120 degrees of the field of view 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.

    Principle: The door mirror is composed of two lenses When we look out from the inside of 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 will AB the outdoor person or object AB into a very small upright virtual image A B, this image just falls in the first focus of the eyepiece L2, L2 plays the role of a magnifying glass, and finally obtains a more magnified upright virtual image A B, which is just near the brightness distance of the human eye, and can see clearly for the situation outside the door.

    Why, then, when you look in from the outside of the door (upside down) through this mirror, you can't see anything?

    When looking backwards, L1 becomes an eyepiece, L2 becomes an objective lens, the indoor scene AB, through the refracted beam after the converging lens L2 should have generated an inverted real image A B, but before the image is imaged, it falls on the divergent lens L1, because the focal length of L1 is extremely short, the final upright virtual image A B is very close to the eyepiece L1, only 2 3cm, and because the aperture of the door lens is very small, the outdoor person has to get close to the eyepiece L1 to inspect, in this way, the distance between the human eye and the image A B is only 2 3cm, This distance is much smaller than the near point of the normal human eye (the near point is the minimum distance that the human eye can see clearly The near point distance increases with age, the near point of normal young people is about 10cm, but the near point of normal people is about 40cm when they are 50 years old), therefore, for outdoor peeps, everything indoors is of course "blind".

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