What are the advantages of infrared lenses compared to ordinary lenses

Many friends are wondering this question: Why are lenses with the same focal length divided into ordinary lenses and infrared lenses? What is the difference between an ordinary lens and an infrared lens? Next, we will briefly explain the difference between the two for everyone: First of all, they have different purposes: In a surveillance environment that does not require infrared light assistance, use an ordinary lens; in a surveillance environment with infrared light assistance, if you want to have a more ideal monitoring effect, you must use an infrared lens; of course, you can also use an ordinary lens with infrared assistance. I can see the picture, but the picture will become blurry. I believe everyone has a deep understanding of this. Second, the prices of the two are different: The price of a professional infrared lens is several times that of an ordinary lens. Why? Because the infrared lens is clear during the day and night, the effect is good and it is naturally more expensive. *Let's talk about the reason why the performance and price of the two are so different: Since the refractive index of glass is different for light of different wavelengths, the position of the focus point will be different. At present, ordinary lenses on the market can gather light with a wavelength difference of about 250nm on the same plane, that is, 430~650nm or 650~ The light in the 900nm range can be focused successfully and present a clear image, which is why the ordinary lens is adjusted clearly during the day and the night vision is blurred, or the night vision is adjusted clearly and blurred during the day. The professional infrared lens uses special lenses, which can gather light from 430~900nm or even longer wavelengths on the same plane, so the vision is clear regardless of day or night. Because the lens material is special, the cost is naturally high. The cost of professional infrared lens is high, and the new problem is coming again. The cost of the machine that everyone makes is high and the profit is low. What should I do? The Chinese are very clever. They apply some coating to the lens and correct the light, and a cheap infrared lens will come out. And no matter good or bad, they are all called-infrared lenses! But what is the effect? How long will the coating take off? Will it evaporate after being heated? The coating does not seem to be so uniform, and some areas are sometimes blurred. What should I do? Use it reluctantly, don't ask too much for bargains.