In order to achieve clear focus for both infrared light and visible light, it is necessary to ensure that their focal planes are on the same plane. The optical correction ability to reduce chromatic aberration is very limited, so it is necessary to use ED glass (ultra-low dispersion glass) lenses, which have ultra-low dispersion, to reduce chromatic aberration and ensure that light of various wavelengths actually focuses on the same plane. Near-infrared does not defocus, thus achieving high definition in both daytime and nighttime 24/7.
Telephoto lenses have stricter requirements for infrared correction, and ED glass must be used for infrared correction to ensure consistent focal plane for infrared light and visible light, in order to achieve true day and night high definition. In fact, many mainstream lens manufacturers use true infrared to achieve high definition in both day and night, which shows the importance they attach to achieving true infrared effects.
Telephoto lenses, in particular, need to pay attention to this because the more lenses there are inside the lens, the greater the chromatic aberration caused by the light passing through the lens, and the greater the deviation of the focal planes of the infrared light and visible light. The general optical correction has minimal influence on the deviation of the focal plane. After focusing, there is a huge difference in clarity between day and night, making it impossible to achieve day and night high definition.
Without infrared correction, when adjusting the focus for clear imaging during the day, the imaging at night is unclear; when adjusting the focus for clear imaging at night, the imaging during the day is unclear. After optical infrared correction, when adjusting the focus for clear imaging during the day, the imaging at night is unclear; but when adjusting the focus for clear imaging at night, the imaging during the day may or may not be clear, depending on the focal length and depth of field of the infrared lenses. Once the lens with infrared correction achieved by using ED glass lenses has clear images, whether it is day or night, the imaging will be clear.
Multi-layer composite coating technology can reduce light scattering loss, improve lens transmittance, and make the image clearer. At the same time, it enhances the transmission of light waves with wavelengths ranging from 750 to 1000nm. The surface of the lens is generally dark green. Infrared multi-layer coating technology can improve the transmittance of near-infrared light, which enhances the high definition effect of infrared lenses.
Typically, lenses with infrared functions only solve the problem of "whether it can be seen", but they do not solve the problem of "whether it is clear". Without infrared correction, especially without ED glass infrared correction, the focal planes of infrared light and natural light deviate from each other, making it impossible to achieve day and night high definition. IR infrared lenses are widely used in various places and can achieve dual-use surveillance for day and night.