What's the difference between a filter and a filter?

Filters are the cheapest accessories that can obviously change the appearance of photos. As the name implies, the filter has the function of filtering light and plays a role of "seasoning" in photography creation. If you can use filters flexibly, you can improve the performance of photographic works. Using filters in black-and-white photography can change the tone of the scene and make the photo closer to nature. The use of filter in color photography can change the color temperature of light source, the color of the subject or play a special visual effect. A filter is actually a piece of glass or plastic placed in front of the camera lens when shooting. There are many kinds of filters, which can be basically divided into several categories: some filters can be used to correct the appearance of photos, others can be used to enhance the effect of photos, and special effects filters can completely change the appearance of photos.

An optical device used to select a desired radiation band. One of the characteristics of optical filters is that no optical filter can make the imaging of celestial bodies brighter, because all optical filters will absorb certain wavelengths, thus making objects darker. The filter is made of plastic or glass, and special dyes are added. The red filter only allows red light to pass through, and so on. The transparency of a glass sheet is almost the same as that of air, so it is transparent because all colored light can pass through it. However, after dyeing, the molecular structure changes, the refractive index changes, and the passage of some colored light also changes. For example, a beam of white light passes through a blue filter and emits a beam of blue light, while green light and red light are very few and most of them are absorbed by the filter. Its main feature is that its size can be made quite large. Thin film filters that usually transmit longer wavelengths are often used as infrared filters. The latter is a low-order, multi-stage series solid Fabry-Perot interferometer. Metal-dielectric-metal films or all-dielectric films with high refractive index or low refractive index are alternately formed on a certain substrate by vacuum coating. The choice of material, thickness and series connection mode of the film depends on the required central wavelength and transmission bandwidth λ.

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