Dog: I see a lot of children and young people also wear glasses, are those also reading glasses?
Lao Tzu: That kind of myopia lens, the lens is a concave lens.
Dog: What is the use of these glasses?
Lao Tzu: Myopia is usually due to poor eye habits, resulting in an elongation of the front and back diameter of the eyeball.
After the light is refracted through the lens, a clear image falls in front of the retina.
Dog: How does the concave lens focus light on the retina?
Lao Tzu: Then we must first understand the imaging principle of concave lenses.
Concave lenses have a divergent effect on light. The light emitted by the object is refracted by a concave lens and becomes a virtual image of shrinking and standing.
Therefore, the parallel light that enters the glasses first passes through the divergence of the concave lens, and then through the convergence of the convex lens (lens), and finally the clear image falls on the retina.
Dog: This method is very good, but everyone's eyes are different, a concave lens can solve everyone's problems?
Lao Tzu: Of course not. Before dispensing the glasses, the refraction is determined, and then different lenses are matched according to this degree.
The higher the power, the more concave the concave lens is, that is, the edge is thicker and the center is thinner, looking like a bottle bottom.
Dog: How heavy is that?
Lao Tzu: It is very heavy, long-term wear height glasses, the bridge of the nose will be pressed by the frame two prints. So now more people like to wear contact lenses.
Dog: Invisible? Out of sight?
Lao Tzu: Contact lenses are not framed, directly cover the lens on the eyeball, so that it is both lightweight and does not hinder movement.
Dog: Wow! This invention is so bold, put the lens in the eye socket!
Concave lenses, where else can they be used?
Lao Tzu: The cat's eye on the entrance door also uses a concave lens.
Cat's Eye can confirm the identity of outdoor personnel before opening the door to ensure the safety of life, usually composed of a combination of a concave lens and a convex lens.
The outdoor object AB, through the concave lens, forms a positive and reduced virtual image A1B1, which falls within the focus of the convex lens. Indoors, through the concave lens, one can see a magnified imaginary image of A2B2.
However, from the outside to the indoor view, because the light is emitted by the concave lens, it is not clear to see, which can ensure the safety of the room.
Dog: This invention is very good, you can meet strangers without opening the door.
Lao Tzu: But the Road is one foot high and the devil is one foot tall, and now the thief has invented the anti-cat eye device!
Dog: How did it come about?
Lao Tzu: Anti-cat's eye is a peeping tool specially designed for "cat's eye", which can peek into the indoor situation from outside the door through "cat's eye".
Using the opposite principle of cat-eye imaging, changing the built-in lens sequence, you can directly observe the indoor situation from the cat's eye outside the door and in the opposite direction. You can also connect external cameras and monitors to capture the situation at home.
Dog: What about seeing it?
Lao Tzu: You think thieves only have this one thing?
The thief uses the anti-cat's eye to see that there is no one in the house, he will use a cat's eye tongs to remove the cat's eye, and then use a folding iron rod with a hook to pass through the cat's eye and use the lever principle to easily open the security door and enter the house to steal.
Dog: So smart?!
Lao Tzu: Didn't expect that?
However, even if the brain is smart and knowledgeable, if the mind is not correct, then no matter how much you learn, it will only be used to do bad things. So a lot of smart people ended up in jail.
Dog: Then my clever little brain melon, but you have to take a little turn [teeth]
Lao Tzu: Okay, let's eat dog food.
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