Optical filter is made of plastic or glass and special dye. The transmissivity of glass is almost the same as that of air. All colored light can pass through it, so it is transparent. However, after dyeing with dye, the molecular structure and refractive index change, and the passing of some colored light changes. For example, when a beam of white light passes through a blue filter, it emits a beam of blue light, while the green light and red light are very few, and most of them are absorbed by the filter.
The filter is used to attenuate (absorb) some light bands in the light wave, or to accurately select a small range of light waves to pass through, while reflecting (or absorbing) other unwanted bands. By changing the structure of the filter and the optical parameters of the film, various spectral characteristics can be obtained, so that the filter can control, adjust and change the transmission, reflection, polarization or phase state of light wave.
There are crystal and blue glass optical filters. AR coating on crystal is used to improve light penetration, while blue glass is used to filter infrared. In addition to special filters for black-and-white and color photography, there are also some filters that can be used in general, such as ultraviolet filters, polarizers, neutral gray filters, soft light filters, fog filters, etc.
Due to the obvious performance advantages of the filter, the filter plays a very important role and is widely used in photography, often as a filter. Let's learn about some knowledge points of filter used as filter.
1. Ultraviolet filter, also known as UV lens, is used to absorb ultraviolet light and a small amount of blue ultraviolet light that can not be seen by human eyes, reduce fog and dew, and enhance the clarity of remote scenery. In addition, it can protect the lens from water and dust.
2. Polarizer, also known as polarizer, needs to adjust the angle to eliminate polarized light. The main functions of the polarizer are: to eliminate the reflection of the non-metallic surface; to darken the blue sky and deepen its tone; to increase the color saturation of the subject; because the polarizer is gray, it also plays a role in blocking light, so it can be used as a gray density mirror.
3. The lens is colorless and transparent. The surface of the lens is corroded with different patterns. It can make the light beam scatter and soften. Soft lenses are often used in portrait shooting.
4. Special effect filters are some filters that can change the normal effect of the image and make the picture present all kinds of wonderful changes. Such as starlight mirror, multi shadow mirror, hollow mirror, dynamic mirror and various magic mirrors.