The filter is an optical device used to select the desired radiation band. One of the commonality of filters is that there is no filter to make the image of celestial objects brighter, because all filters absorb certain wavelengths, which makes the object darker. The filter is made of plastic or glass and added with special dyes. The red filter can only let red light pass through, and so on. The transmittance of the glass sheet is originally similar to that of air, and all colored light can pass through, so it is transparent, but after dyeing the dye, the molecular structure changes and the refractive index also changes, which changes the passage of certain colored light.

　　The filter is very useful. Widely used in the photography industry. A color filter is an optical filter that expresses colors. It can accurately select the small range of light waves to be passed, and reflect other undesired wavelengths. Chromatic optical lens Chromatic optical filter is usually installed in front of the light source, so that the human eye can receive the saturated light of a certain color.

　　All optical components are precision instruments, especially optical filters, and the surface is easily scratched. Improper cleaning and storage methods may damage the surface film of the filter, reduce its application performance and shorten its service life. Therefore, the correct maintenance method is extremely important.

　　 Below we will discuss the small details that should be paid attention to in the ordinary use of optical glass filters:

　　1 、In the process of normal use, you should take and place as carefully as possible, and pay attention to the external environment to prevent the filter from being scratched.

　　2. Wear finger cots when touching the filter to avoid corrosion of the substrate surface by salt and acid on your hands.

　　3. When taking the filter, hold the edge of the filter in your hand. Glossy.

　　4. The filter should be placed on a soft and clean object, not on glass, metal, table, or dirty paper.

　　 5. When storing, it should be placed in clean capacitor paper or special lens cleaning paper. The best storage temperature should be around 23℃, and the humidity should not be higher than 40%. It is better to put it in a dry storage cabinet.

　　 6. Clean up immediately when you find stains on the surface. Because dust can easily scratch the surface.

　　7. If the acidic substance left by the finger stays for too long, it will easily react with the surface coating material and become a permanent stain. Clean the surface stains of the filter in time.

　　 8. If there are stains or fingerprints on the surface, you can wipe it with an ethanol focusing lens or similar functional solvents. The specific method is as follows: wear a dust-free finger cot on your fingers, soak the towel with absolute ethanol, drag the edge of the towel soaked with ethanol, and move it in a single direction on the surface of the filter. Use as much force as possible during the wiping process, too much pressure may damage the surface of the filter. The purpose of using the solvent is to dissolve the sticky deposits on the surface of the filter. But it is worth reminding that any cleaning may reduce the surface grade at the micro level.

　　Convex lens imaging law:

　　(1) A condition that the convex lens needs to be fulfilled to become a real image is

　　 (2) Conjugate imaging means that the size of the object distance and the image distance can be interchanged. In the two cases, it becomes an enlarged and reduced inverted real image.

　　 Looking through a convex lens at a timepiece other than the double focal length, the image of the second hand still rotates clockwise, because this aspheric lens is an inverted real image, and it is still in the normal direction when viewed backwards, so it is still clockwise Direction rotation.

　　?????? (1), the lens is represented by the lens symbol (a line segment has two V-shaped signs at both ends), draw the main optical axis, mark The light center and focal point are based on the intersection of two refracted rays of the three special rays of the lens (generally the light that passes through the optical center and the light parallel to the main optical axis is better), and the image formed by the lens can be obtained. Features (such as virtual reality, size, front and back, etc.).

　　???? (2). When the lens is imaging, all the light shining on the lens from each point on the object is imaged in the same position, blocking a part, and It does not affect the imaging of other light directed to the lens, so the complete image can still be seen, but the brightness of the image on the screen will become darker due to the decrease of the light incident on the image.