Filter is an optical device used to select the required radiation band. One of the commonalities of filters is that no filter can make an image of a celestial body brighter, because all filters absorb certain wavelengths, making the object darker.

Filters are made of plastic or glass with special dyes. Red filters only allow red light to pass through, and so on. The transmittance of glass is similar to that of air. All colored light can pass through it, so it is transparent. However, after dyeing with dyes, the molecular structure changes and the refractive index changes, so does the passage of some colored light. For example, when a white light passes through a blue filter, it emits a blue light, while green light and red light are very few, and most of them are absorbed by the filter.

HCVAC vacuum optical coating machine is applied to lens, lens, vehicle, digital camera, smart phone, projector, filter and other industries. It is specially designed for the production of optical film products with few layers but high production capacity and high efficiency. The antireflection film can reduce the surface reflected light of lens and increase the transmission light. When there are many lenses, they must be low reflection. In addition to multilayer films, double-layer films with specific wavelengths are also used on MgF2 monolayer and laser head, which can be coated on plastic products at low temperature.