The main optical components of the telescope are the objective lens, eyepiece and prism. The coating can reduce light loss and reflection caused by reflection, and improve the transmission rate and contrast of light.
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A limiting factor for binoculars that reflect light. When light hits ordinary glass, 4% of the light is reflected from the glass surface (the glass itself absorbs part of the light because it passes through). The telescope has an average of 10-16 glass surfaces, and its light loss may be 50% of the light that initially enters the objective lens. % Or more, and worse, all reflected light will produce flash and ghost images after multiple reflections inside the telescope.
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Coating a thin vacuum coating on the surface of the filter, which has a specific chemical composition (usually magnesium fluoride-MgF2). The amount of reflected light on the surface of each filter is reduced to 0.25 or 0.5%, and the transmitted light and contrast are better than those of ordinary coatings.
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The thickness and density of the coating must be absolutely standardized, otherwise problems such as unexpected reflections will occur.
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So, how do you need to accurately distinguish the type of coating?
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Coating is the most confusing word. In many cases, the interpretation of the telescope can lead people astray. For the sake of distinction, the general explanation is as follows:
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Optical coating: This means that only one or more lenses already have an anti-reflection film on the surface of the lens;
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Full coating: means that all glass surfaces in contact with the air are coated (in most cases, this means less; if a plastic mirror is used, most of them are uncoated);
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Multi-layer coating: One or more lenses are coated with multiple layers, and some lenses can be coated with only a single film or some lenses without coating;
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Full multi-layer coating: All glass surfaces in contact with air have multi-layer coatings.
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If you have enough money, buy fully-coated binoculars because of their higher optical transmission and clearer imaging. This is why fully-coated binoculars are more expensive than ordinary telescopes.