Why do spectacle lenses fog up?
The fog on the surface of the lens is essentially related to the saturation pressure and water vapor liquefaction. The air is full of water molecules, which are constantly doing irregular movements. When there is no temperature difference, water molecules keep hitting the surface of the lens and will keep bouncing off. The lower the temperature, the slower the speed of movement. Therefore, when water molecules hit the cold lens from the hot air, on the one hand, they move too slowly to fly out in time. On the other hand, because of the relatively low temperature of the lens itself and its vicinity, the water vapor will liquefy. As a result, more and more water will accumulate on the lens and form small droplets, eventually forming a foggy layer. As the lens heats up, the mist evaporates back into the air, and the fog disappears.
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Who are suitable for progressive lenses?
A progressive piece is suitable for most old people to wear. The proper person is the one who has the visual needs of the long, medium and short distance cares about beauty, and is willing to accept new things. In order to avoid binocular vertical prism differences, for the wearer whose equivalent spherical lens with anisometropia is more than 2D, especially if the difference in refractive power of the vertical meridian is more than 2D, it should be checked with caution. Opticians whose vision needs do not match the progressive lens design, like dentists, often experience blurred vision when working with the far side of the lens to look closer.
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How to Choose Glasses for Diamond Face Shape?
After learning the features of diamond face shape, you should know how to choose glasses for diamond face shape. Since there are a lot of pointed features on the face, the best option is to use eyeglasses that have soft rounded curves instead of harshly pointed angles. So, look at the following advice.
Cat eyeglasses: Cat eyeglasses would be a good choice for a diamond face shape. These glasses frames have rounded bottoms so as to hide away the pointed chin and the narrow jawline of the diamond.
Round eyeglasses: Round eyeglasses are also suitable for diamond face shape because the round curve of the glasses hides the sharpness of the pointed chin. Glasses with colored frames are appealing in the case of diamond face shape people.
What are the causes of lens damage?
When the force area of the lens is small, the impact resistance of the lens is worse. When subjected to the impact of external forces, the lens will naturally be squeezed and cause breakage.
In particular, some lenses with low degrees and high refractive index are possible to cause this phenomenon. When the frame fell from a height due to wrong placement, there is a collision between the edge of the lens and the ground or hard objects. It will produce a broken or collapsed edge. In the process of the lens falling from high, the impact force is larger, and the stress point is smaller. When the glasses are falling, the upper edge of the lens, the convex groove of the upper frame, squeezes against the lens. The middle part of the upper half is easy to cause edge collapse. In the process of processing the template, the template is not accurate, so that the glasses side and the frame can not be uniform fusion, and the force of the lens is uneven. It will be easy to lead to greater stress in some parts, resulting in edge collapse.
Shorter lens beam
When you choose a glasses frame for kids, you must pay attention to that the lens beam must be short. The size of the lens beam stipulated by the national standard is 13~22mm. As a child, it should be controlled under 18mm. Otherwise, the position stability of the glasses will be poor.
Finally, they can not casually wear other people's glasses. The strength of each person's glasses, the distance between the optical centers of the two lenses, the length of the temple are different. So they can not casually wear other people's glasses.
