Filter is an optical device used to select the required radiation 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. Color filter These are flat glass or gelatin sheets of various colors with a transmission bandwidth of hundreds of Angstroms. They are mostly used in broadband photometry or installed in stellar spectrograph to isolate overlapping spectral levels. Its main feature is that the size can be made quite large. Thin film filter Generally, the transmission wavelength is long and is mostly used as infrared filter. The latter is on a certain film base. Principle The filter is made of plastic or glass with special dyes. The red filter can only let the red light pass through, and so on. The transmittance of glass sheet is similar to that of air, and all colored light can pass through, so it is transparent. However, after dyeing with dye, the molecular structure changes, the refractive index also changes, and the passage of some colored light changes. For example, when a white light passes through a blue filter, it emits a blue light, while there are very few green and red light, and most of them are absorbed by the filter. Effect The filter plays a great role. Widely used in photography. Why is the main scene always so prominent in the landscape paintings taken by some photographers and how to do it? This uses filters. For example, if you want to take a yellow flower with a camera, the background is blue sky and green leaves. If you take it as usual, you can't highlight the theme of "yellow flower", because the image of yellow flower is not prominent enough. However, if a yellow filter is placed in front of the lens to block the green light scattered by some green leaves and the blue light scattered by the blue sky, an

Cylindrical lens is an aspherical lens, which can effectively reduce spherical aberration and chromatic aberration. It is divided into flat convex cylindrical lens, flat concave cylindrical lens, biconvex cylindrical lens, double concave cylindrical lens, meniscus cylindrical lens, cylindrical intersection cylindrical lens and special-shaped cylindrical lens. It has one-dimensional amplification function. Cylindrical lens is mainly used to change the design requirements of imaging size. For example, convert a point spot into a line spot, or change the height of the image without changing the image width. It can be used in linear detector lighting, bar code scanning, holographic lighting, optical information processing, computer and laser emission. Optical cylindrical mirror is also widely used in high-power laser system and synchrotron radiation beam line. At the same time, the requirements for cylindrical mirror parts are becoming higher and higher, especially in high-precision testing instruments and devices such as cavity plate of high-power laser resonator and long-distance off-line interferometer. Manufacture of cylindrical lens Including rough grinding, fine grinding, polishing, centering and edging.

Prism, a transparent object surrounded by two intersecting planes that are not parallel to each other, used for splitting or dispersing light beams. Prism is a polyhedron made of transparent materials (such as glass, crystal, etc.). It is widely used in optical instruments. Prisms can be divided into several types according to their properties and applications. For example, in spectral instruments, the "dispersion prism" that decomposes the composite light into spectrum is more commonly used as equilateral prism; In periscope, binocular telescope and other instruments, changing the direction of light to adjust its imaging position is called "total reflection prism", which generally adopts right angle prism. Function of reflection prism: when the reflection prism (or reflector) is used as the reflector for ranging, the reflection prism receives the optical signal sent by the total station and reflects it back. The total station sends out the optical signal, receives the optical signal reflected from the reflecting prism, calculates the phase shift of the optical signal, so as to indirectly obtain the time of light passing, and finally measure the distance from the total station to the reflecting prism. Principle of reflection prism: the working principle of reflection prism is actually the reflection law and refraction law of light. When light is reflected in the same medium, its reflection angle is equal to the incident angle; When light is incident from one medium perpendicular to two medium planes to another medium, it will not be refracted.