Lens, ADL MZ38X4179DPFIR-T 41 – 1560mm 2/3″ 38X zoom

Technical Note:

The “fog free” function on this lens is designed to improve image quality in obscured weather conditions (fog, mist, dust, smoke, etc).  This lens uses a special filter to remove all light wavelengths below 800nm (mainly visible light) from the image and transmit light greater than 800nm into the near infra-red light spectrum.  The science behind this feature is that different wavelengths of light can penetrate through air-borne water droplets and particulates (fog, mist, dust, smoke, etc) to varying degrees.  When light encounters water droplets or dust particles it is deflected from the direct path making the image increasingly hazy.  Infra red light has a longer wavelength than visible light so has a much better chance of “going around” the particles and reach the camera sensor!  The filter is deployed because visible light and infra red light focus at a slightly different distance meaning that if the lens is focussed at a point in the infra red spectrum the visible light will blur.  When you remove the visible light the image will appear sharper despite the amount of light reaching the sensor has decreased.