The lens is an indispensable part of the infrared thermal imager. Its function is to converge the infrared radiation of the target on the infrared detector, and through photoelectric conversion and image processing, it finally forms an image with good contrast. The quality of the infrared lens largely determines the performance of the infrared camera.
The infrared lens should be specially designed according to its working band to optimize its performance. The infrared materials used in the infrared lenses of different bands are also different.
Generally speaking, infrared lenses do not allow vignetting. For the lens used in the infrared cooling detector, if the lens has vignetting, it cannot meet the 100% cold diaphragm efficiency design principle, and stray radiation will affect the performance of the infrared thermal imager.
3. Focal length and field of view
An infrared lens is usually identified by its focal length. As the focal length increases, the field of view of the lens narrows. Conversely, as the focal length decreases, the field of view becomes wider.
Infrared lenses can generally be divided into single-field lenses, multi-field lenses, and continuous zoom lenses. Since the infrared continuous zoom lens can realize target search and continuous tracking of targets at different distances, it has been widely used in many fields.
4. F number
The F number of the infrared lens determines how much the target radiant energy enters the infrared thermal imager. The smaller the F number, the larger the size of the infrared lens under the same focal length.
Most infrared materials have a high refractive index, and the lens in the infrared lens needs to be coated with a high-efficiency antireflection coating to increase the transmittance of the infrared lens. As the number of lenses in the lens increases, the transmittance of the lens gradually decreases.
6. No heating
Since the refractive index of infrared materials varies greatly with temperature, when the ambient temperature changes, the infrared lens will produce a corresponding defocus. The infrared lens also adopts two methods of active and passive to achieve athermalization to ensure that the focal position of the lens does not move when the temperature changes.