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The lens of infrared thermal imager is usually made of germanium glass with high refractive index. Germanium glass is only transparent to infrared light, but opaque to visible light and ultraviolet light. We compared the infrared thermal imager lens with the ordinary camera lens. The infrared lens with special germanium glass can concentrate the light in a longer wavelength range on the same plane, and you can see objects through infrared imaging no matter in the day or at night. The reserves of germanium are not low, but the extraction of high concentration germanium is very difficult, so the production cost of germanium lens is relatively high, and the market price is often higher than that of ordinary camera lens.
Infrared lens
The lens of an ordinary camera is usually made of optical glass, and its special function is, of course, to refract light (usually referred to as amplifying objects). Usually, optical glass is synthetic. The main reason for the insufficient exposure of ordinary cameras / cameras to infrared rays may be the photosensitive elements and lenses. The attenuation of infrared light by ordinary lens depends on the lens material, coating and wavelength range of infrared light.
Ordinary optical lens
So in the real world, what is the difference between thermal imaging and visible light? Infrared thermal imaging is different from visible light in many ways, mainly in the following points:
1. Imaging Principle
The imaging principle is basically the same. Imaging devices image light waves within a specific wavelength range. The wavelength range of visible light in nature is 0.39 μ M to 0.78 μ m. The wavelength range of infrared thermal radiation is 0.75 μ M to 1000 μ m。 Speaking of this, I need to stop. Didn't I say that thermal imaging is not based on temperature (temperature difference)? Why is infrared thermal radiation involved? It must be emphasized that as long as their temperature is higher than the absolute zero value of -273 ℃, infrared radiation will be generated. Thermal imaging is to detect infrared energy (heat) through non-contact, convert it into electrical signals, and then generate thermal images and temperature values on the display. But if you want to know more about thermal imaging, you must always keep this in mind. Thermal imaging devices also receive light waves (infrared bands) that are invisible to the human eye.
2. Detector
The core detector of the imaging equipment is infrared thermal imaging. The visible light has CCD and CMOS. The thermal imaging has cooling type and non cooling type (the difference is whether it has a small cooler, which is mainly used to control the focal length). Plane temperature, please remember whether the previous temperature difference is particularly emphasized? Taking the temperature of the focal plane as the reference temperature, its content is not specially expanded). The main difference is that the visible light CCD / CMOS can sense the light wave in the visible light band, while the thermal imaging detector can sense the thermal radiation light wave in the infrared band. Infrared thermal imaging detectors are divided into many types according to different manufacturing processes and packaging materials. The more macroscopic feeling is that the infrared thermal imaging detector is more expensive than the visible light CCD, and the visible light CCD is orders of magnitude or more expensive. This is also the current situation. One of the main reasons for the narrow application range of infrared thermal imaging technology.
3. Lens
The main difference between lenses is that thermal imaging lenses must be made of special materials. The main reason is that infrared thermal radiation cannot penetrate glass (silicon), so special lenses made of metal materials such as germanium and chromium are used. This also causes the price of thermal imaging lens to be a little higher than that of optical lens, which also increases the price of the whole machine.
4. Image
The difference between images is that visible light imaging is color, RGB three channel, while thermal imaging is gray, and the original thermal imaging image is single channel. The color thermal imaging we see in the market is pseudo color, which is manually converted in the later stage. Usually, there are many kinds of false colors, which can also be configured. In addition, the image size of thermal imaging is smaller than that of visible light. Nowadays, the typical thermal imaging has 384 and 640, and the largest 1024 has only been released in recent years, but the visible light is now 1080p or 400W, which has become the mainstream in practical applications in China.
5. Application Scenario
Visible light is often used in good light conditions during the day or at night. Although there are many star level devices available now, the imaging effect is not satisfactory at night with poor light, but thermal imaging can work all day. At night, it can still be imaged. Of course, thermal imaging also has its disadvantages. After all, imaging is based on temperature difference. Therefore, in rainy weather and bad low temperature conditions, the imaging quality will also decline, or even blur. For example, if blue clothes fall into the blue sea, they cannot be seen with visible light devices. An object with a uniform surface temperature of 30 ° is placed in a scene with a temperature of 30 ° and cannot be seen using a thermal imaging device. Therefore, in practical application, appropriate solutions should be formulated according to the site conditions and equipment characteristics. 报错 笔记
