Filter is an optical device used to select the required radiation wave band.
A common feature of filters is that no filter can make the imaging of celestial bodies brighter, because all filters will absorb certain wavelengths, making objects darker.
The principle of the filter is that plastic or glass pieces are added with special dyes. After vacuum coating or baking, the molecular structure changes, the refractive index changes, and the passage of some colored light changes.
The filter uses TiO2 and SiO2 thin film systems evaporated by electron beam (EB), which have important applications. However, with conventional evaporation technology, even if the temperature of the substrate is higher than 300 ℃, the film still shows obvious columnar structure characteristics. As the film with this columnar structure contains a large number of voids, the refractive index of the film increases with the moisture absorption of the film filter,
The central wavelength of the filter will have a significant drift. In order to characterize this structural property, the aggregation density P is proposed, which is defined as the ratio of the volume of the solid part to the total volume of the film. Therefore, it is a physical quantity describing the degree of film porosity.
The filters produced by Borisun Optics Co., Ltd. can be divided into the following types:Bandpass filter, narrowband filter, ultraviolet filter, neutral density filter (attenuator), dichroic mirror, beauty instrument filter, splitter, reflector, long wave pass filter, short wave pass filter, notch negative filter.