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Day also "understand" night black different infrared surveillance lens

Because infrared and visible light refractive index is different, through the lens will produce refraction and dispersion. After dispersion, infrared and visible light will be focused on different focal planes. CCD/CMOS cannot meet the requirements of clear infrared and visible images at the same time, which is why ordinary lenses cannot achieve infrared functions.

Lens correction can be divided into several kinds: no infrared correction, infrared optical correction, ED glass and other materials infrared correction. At present, many lenses on the market are only through optical correction, infrared and visible light focal plane can not achieve the same, but in the short focal length segment of the infrared effect can be reluctantly accepted. By using ED glass, the effects of infrared correction of lens materials are almost the same, "true infrared". Infrared is a topic of discussion, but monitoring lens field different correction is completely different effects, infrared lens do not have what "hole"?

Introduction to infrared lens - optical correction

In general, except in special cases, a single spherical lens cannot correct for chromatic aberration. Positive lenses produce negative chromatic aberration, and negative lenses produce positive chromatic aberration. In order to reduce the chromatic aberration, different refractive index and chromatic aberration glass combination can be used to eliminate chromatic aberration.

The double lens group or double gluing lens group with proper shape of positive and negative lenses is a simple structure with achromatic possibility. This method is commonly used in optical infrared correction.

After optical correction, the distance between the focusing planes is reduced (but not eliminated) due to the reduced dispersion, the refraction separation of infrared and visible light is reduced. For the lens with short focal length, after optical correction, the focal plane deviation of infrared and visible light is small, which has little impact on image sharpness. However, with the longer the focal length, the dispersion will be gradually amplified, and the greater the deviation of the focal plane of infrared and visible light, the optical correction cannot make both images clear at the same time.

ED glass correction is the core of infrared lens

In order to make infrared light and visible light clear at the same time, the focusing plane of both must be on the same focal plane. The ability of optical correction to reduce color difference is very limited, so we must use ED glass (ultra-low dispersion glass) lens, ultra-low dispersion, reduce color difference, and ensure that all wavelengths of light are actually focused on the same plane, near infrared does not focus, so as to achieve 24 hours of hd day and night.

The telephoto lens has more strict requirements for infrared correction, and must use ED glass for infrared correction to ensure that infrared light and visible focal plane are consistent, so as to achieve true hd day and night. In fact, from the use of ED glass mainstream lens manufacturers, seiko lens are selected ED glass lens, the use of true infrared true hd day and night, we can see that the mainstream lens manufacturers to achieve real infrared effect.