What do Infrared (IR) Lenses Do?
An infrared lens is an objective lens suitable for the infrared wavelength. The infrared wavelength refers to the three wavelengths of 1-3um, 3-5um and 8-14um, also known as the three atmospheric windows. Infrared objective lens has been widely used in temperature measurement, medical diagnosis, security supervision, forest fire prevention, agricultural planting and military reconnaissance, tracking, guidance and other fields, is a very important lens type.
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Because infrared light is much longer than visible light, the detector pixel size used is relatively large, and the infrared objective lens generally does not have high requirements for the line frequency, and the design of the infrared objective lens is relatively simple. However, infrared objective lenses also have some characteristics and difficulties in their own design, such as fewer options of materials, design for different types of sensor , stray light processing problems.
The biggest difference between the normal visible light objective and the infrared objective is that the material used is different. In general, the visible light wavelength uses normal optical glass and some crystal materials. Normal glass materials contain hydroxyl, which has a large absorption in the infrared wavelength, and can usually only be used in the near UV-visible light-near-infrared wavelength, which can not cover most of the infrared wavelength.
Types of Infrared Lenses (IR Lenses)
According to the different wavelengths used, the infrared objective lenses on the market are generally classified by wavelength, which can be divided into short-wave infrared lenses, medium-wave infrared lenses and long-wave infrared lenses. The objective lens of different wavelength is suitable for different atmospheric Windows, and the user should choose the objective lens according to his own application and use environment.
SWIR Lenses, LWIR Lenses, MWIR Lenses, and NIR Lenses
As one of the world’s foremost producers of high performance IR lenses, we carry a wide selection of SWIR lenses, LWIR lenses, MWIR lenses, and NIR lenses. These lenses are ideal for use in the infrared region, with applications including industry, medicine, scientific research, and defense.
- Short Wave Infrared SWIR Lenses can use more optical materials, and the supporting detector resolution is higher, so the imaging quality is close to that of the visible light lens, which can be used for accurate measurement and control.
- They function best when used with radiation between 800 and nm. These SWIR Lenses are used for noninvasive quality control and machine vision as well as in medical diagnostics and anti-counterfeiting applications. Though SWIR light is invisible to the human eye, a SWIR camera can produce high-resolution images with detail equal to a standard camera under regular light conditions.
- Unlike medium and long-wave infrared lenses, the passive imaging of short-wave infrared lenses mainly collects the reflected light of the surface of the object, which is similar to that of visible light lenses. Compared with visible light lenses, short-wave infrared lenses have the advantage that the light in this wavelength is relatively strong and can pass through smoke, which is suitable for imaging in more harsh environments. And short-wave infrared can detect the certain materials, such as silicon wafers, so it has important applications in the semiconductor field. At the same time, some objects can absorb short-wave infrared, such as water, metal, etc., so in a specific scene, short-wave infrared lenses can present different visual characteristics from visible light lenses, and have unique advantages in detection and screening applications.
- This is even though short-wave infrared radiation from room-temperature objects is negligible. However, when the temperature rises and the radiation wavelength shifts to short, the short-wave infrared lens can also detect the heating of high-temperature objects, as a supplement to the medium-wave infrared and long-wave infrared thermal imaging. At the same time, short-wave infrared is also the main irradiation distribution of atmospheric glow, which makes short-wave infrared lens play an important role in the development of night vision technology.
How Does An Infrared Lens Function?
The human eye, akin to an optical device, possesses a sensory component known as the retina. Similar to conventional cameras, the eye receives and converts radiation from the visible light spectrum into images.
However, both the retina and standard cameras lack the ability to detect infrared rays.
Fortunately, IR cameras serve as effective tools for detecting this form of light. Infrared cameras necessitate specialized components including a custom lens, infrared filters, and sensors to capture IR light.
Notably, the operation of infrared camera lenses differs from that of conventional camera lenses.
An infrared lens operates by capturing the infrared light present in the environment and redirects it towards the camera sensor. This process aids in the creation of clear thermal images. IR lenses designed for use in infrared cameras are capable of capturing imperceptible heat or IR radiation within extended wavelength ranges, typically spanning from 700 to 900 nm or beyond.
Material Selection
Common used infrared crystal materials include germanium, silicon, zinc sulfide, and zinc selenide, these materials are the most frequently used in the design of infrared objectives, these materials have a high refractive index, which is conducive to aberration correction. In addition, CaF2, sapphire, CdTe, and other materials will also be used, and the frequency of use is relatively lower. Infrared quartz can also be used in the design of infrared objectives but is limited to the near-infrared wavelength. Their optical parameters are as follows:
Refractive index
Transmission spectrum
CaF2
1.414@3.5um
0.23-9.7um
Ge
4.033@3.5um
2-15um
CdTe
2.677@8.0um
6-22um
Sapphire
1.695@3.5um
0.2-5.5um
Si
3.428@3.5um
1.36-11um
ZnSe
2.417@8um
0.55-18um
ZnS
2.223@8um
0.42-18um
Crystalline materials are generally expensive. In addition to these crystalline materials, infrared glass can also be used as a material for the manufacture of infrared objectives. The most common infrared glass is chalcogenide glass, chalcogenide glass is S, Se, and Te As the main components, combined with AS, Ge, P, Sb, Al, Si, and other elements to form a glassy substance, different chalcogenide glass brands have differences optical characteristics, the glass material selection should be based on the need to the atmospheric window.
Chalcogenide glass has a small refractive index temperature coefficient and a low dispersion coefficient, so chalcogenide glass is usually considered in achromatic and non-thermal optical designs. In addition, the price of chalcogenide glass is generally lower, which is conducive to the cost control of the objective lens.
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The human eye cannot see infrared light since this light lies beyond the visible light spectrum. However, thanks to infrared optics, it’s possible to capture infrared light.
But what is infrared optics?
Infrared (IR) optics refers to any device that can register, display and emit infrared radiation. These devices use optical elements such as an infrared filter, mirror, and infrared lenses to capture infrared light.
An IR lens captures infrared light that is virtually impossible to see with the naked eye. While a normal camera lens captures images of objects that radiate light that is visible to the eye, an infrared lens detects electromagnetic radiation, which is the light that lies beyond the visible spectrum.
Moreover, an infrared lens depends on heat rather than light to record images. Since IR light can be felt as heat, an infrared lens can be able to express the heat value of an object that radiates heat.
Infrared lenses have a wide range of industry applications. For instance, they are used in thermal imaging cameras by medical professionals. IR technology is also used by electricians and building inspectors to detect leaks, corrosion, and other building deterioration dangers.
Want to learn more?
This article explores everything you need to know about IR lenses and how they work.
How Does an Infrared Lens Work?
The human eye is an optical device with a sensor called the retina. Regular cameras work very much like the naked eye, as they receive and turn radiation from the visible light spectrum into an image.
Unfortunately, a normal camera, just like the retina, cannot detect infrared rays.
The good news is that we can use IR cameras to detect this light. Infrared cameras require a custom lens, infrared filters, and sensors to capture IR light.
Notably, infrared camera lenses work differently from regular camera lenses.
An infrared lens works by capturing all the IR light bouncing around and redirects this light to the camera sensor, which helps create a clear thermal image. IR lenses used in infrared cameras capture invisible heat or IR radiation in extended wavelength ranges of 700 to 900 nm or more.
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