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Переведите на русский язык следующий текст:
What are the purposes of lens tints and coatings?
Lenses of any material can be treated with coatings to give the lenses desired properties. Scratch-resistant coatings applied to the front and back of a lens can reduce the risk of sight-marring scratches for glass and plastic lenses. Ultraviolet-resistant coatings can be applied to all lenses; they are not needed for polycarbonate lenses, which have built-in ultraviolet resistance. Antireflective coatings, similar to those on microscope and camera lenses, reduce glare by blocking reflected light, a benefit that is especially important for night driving. Antireflective lenses also make lenses appear thinner, a cosmetic benefit. A wide variety of tints and coatings are available for modern lenses:
Glass lenses are tinted by adding oxides to the glass during the manufacturing process. Plastic lenses can be tinted in a wide variety of shades and colors by dipping the lenses in special dyes. Tints increase comfort in bright light situations, reduce glare from computer screens or fluorescent light, and make a fashion statement. Many eye care offices and optical shops custom-tint lenses in-house in a matter of minutes. If the tint is on the surface of a lens, the color and/or the shade can be changed.
Photochromic lenses change in color and light transmission when exposed to different light intensities. The rate of darkening depends on the ambient temperature. These lenses do not become as dark when driving because the car's windshield absorbs some of the ultraviolet light that causes the lenses to darken. Photochromic lenses are now available in plastic as well as glass, and they may be either brown or gray in color.
Polarizing lenses are very useful in protecting eyes from reflections when skiing or participating in water sports. They are available in plastic, glass, and high-index materials, but they are relatively expensive compared to other lenses.
Ultraviolet protective lenses protect the eyes from ultraviolet sun rays that have been shown to cause cataracts and certain diseases of the eye. If you spend a lot of time outdoors, have your lenses anti-UV coated. The best eye protection from UV radiation is a good pair of sunglasses that is rated to block 99 percent to 100 percent of the full UV spectrum. The lenses should filter wavelengths up to 400 nanometers to cut out all harmful rays. UV coating can be applied to all glass and plastic lenses, except polycarbonate, which doesn't need coating because it absorbs virtually all UV rays.
Mirror-coated lenses are coated with a layer of reflective material that greatly reduces the amount of heat entering the eyes. However, these lenses reduce visual acuity and are somewhat like looking through a two-way mirror. This kind of coating is purely cosmetic and frequently seen on glasses worn by state troopers. Mirror coatings come in a number of colors and are highly reflective. They usually are applied on sunglass-dark lenses. The persons looking at the wearer do not see the eyes of the wearer.
Anti-reflective coatings (A-R coatings) are metallic oxide coatings that are vacuum-applied to the lens surface to reduce reflections from the front lens surface and eliminate reflections from the back. This reduced amount of reflection enhances the appearance of the glasses and also allows more light to pass through the lenses, which can improve vision in low-light situations. Anti-reflective coatings also provide some protection from scratching.
Scratch-resistant coatings (also known as "hard coat") are applied to the front and back surfaces of lenses to protect against accidental scratching and to improve durability. Some high-quality lenses come from the factory with scratch coatings already applied. No coating can make lenses completely scratch proof.
How do you read an eyeglass prescription?
A prescription for eyeglasses contains the powers for the lenses of each eye (including a reading addition if necessary), information on the separation of the lenses, and sometimes special requirements such as types of tinting, coatings, and so on.
Although each eye doctor writes a prescription in a somewhat different way, it usually contains the same elements. The lens correction for nearsightedness is indicated by a minus sign (-), while a plus sign (+) indicates farsightedness. Cylindrical lenses for astigmatism are designated by cyls., cx, or (x).
Let's analyze the following prescription:
O.D. -3.00 D c/w -2.00 D cx 180