Avantier
  • |

The Complete Guide to IR Lenses

Product Highlights

  • Infrared (IR) lenses are specialized optical elements designed for use in the infrared spectrum, beyond visible light. 
  • They gather and focus infrared radiation, enabling thermal detection and imaging. 
  • Made from materials like germanium and zinc selenide, these lenses are transparent to infrared wavelengths, suitable for applications in industry, medicine, research, and defense. 
  • IR lenses come in various types such as SWIR, LWIR, MWIR, and NIR lenses, each optimized for specific wavelength ranges. 
  • They play crucial roles in thermal imaging, non-invasive diagnostics, security surveillance, and defense operations. 
  • Customizable options that Avantier offers ensure precise performance and application suitability.

The Complete Guide to IR Lenses

What do Infrared (IR) Lenses Do?

An infrared objective 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.

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.

MWIR Lens
IR Lens
IR Lens

Structure of Lens

Let’s take a moment to review the anatomy of the lens here. 

An imaging lens can also be referred to as a machine vision lens, objective lens or objective, or simply as a lens. For convenience, we will use “lens” in the subsequent sections to refer to the imaging lens.

Diagram of a lens
  • Focus Adjustment Ring: Rotating this adjusts the focal point of the lens. The distance between the first lens surface and the object is known as the working distance.
  • Iris/Aperture Adjustment Ring: Rotating this alters the size of the aperture stop within the lens, thereby changing the F-number (f/#). Apart from regulating the amount of light passing through the lens, the f/# also influences various critical aspects of lens performance.
  • Thumbscrews: These are used to temporarily lock the focus and/or aperture settings to prevent unintended adjustments.
  • Lens Information: The lens information, typically found on the lens barrel, includes details such as focal length, minimum f/#, part number, and manufacturer.
  • Working Distance Range: This indicates the specified range within which the lens can focus, also known as the object distance range.
  • f/# Tick Marks: These marks on the lens barrel indicate where to set the aperture adjustment ring to achieve a specific f/#.
  • Filter Thread: This is where machine vision filters can be attached if the first lens element does not extend beyond the lens barrel. For wide-angle lenses or when the first element protrudes, an additional adapter may be required.
  • Camera Mount: This is where the lens is attached to the camera, with common mounts including C-Mount, F-Mount, TFL-Mount, and S-Mount. More information on lens mounts can be found in the Lens Mounts section.
  • Rear Protrusion: This refers to how far the lens extends into the camera beyond its shoulder. Caution is advised to avoid interference with internal camera components such as IR-cut filters or electronics.
  • First Surface: This can either be the first optical lens element visible outside the lens barrel or the lens barrel itself. The working distance is measured from this surface to the object.
  • Last Surface: This can either be the final optical lens before the sensor or the lens mount.
  • Lens Shoulder: The part of the lens that makes contact with the camera flange.
  • Overall Length: This is the distance from the first lens surface to the lens shoulder, excluding the camera mount since it will be attached to the camera.
  • Flange Distance: The distance from the mounting shoulder to the image plane, standardized to ensure compatibility between the lens and camera for different mount types.
  • Image Plane: The location where the lens forms an image, typically the camera sensor.

Core Components

Cooled and uncooled infrared detector

  • Cooled infrared detector
    • Infrared detector is the core component of infrared imaging products, which is divided into cooled type and uncooled type. For medium-wave infrared and long-wave infrared, both the structure of the objective lens and the objective itself produce radiation at room temperature. In order to reduce thermal noise and obtain better image quality, the detector generally needs to be cooled.
    • The operating principle of the cooled detector is based on the photoelectric effect caused by the absorption of infrared light by the sensitive material. The cooled detector needs to work at low temperature of liquid nitrogen, and the equipment is expensive and the cost is high. However, the cooled detector has high sensitivity, long detection distance and stable performance, and is generally used in high-end fields such as aerospace and military.
    • To achieve 100% cold stop efficiency, the general stop position coincides with the cold stop, and the stop is behind the lens. This causes the symmetry of the lens to be broken, the correction of off-axis image quality is relatively difficult, and the lens size will also increase. There are also designers who design the lens as a refraction secondary system, so that although the diameter of the lens is small, the structure of the lens will be complicated.
Cooled MWIR lens
  • Uncooled type detector
    • Uncooled infrared detectors are mostly used in long wavelength infrared. The thermal effect produced by infrared light is used, and the infrared radiation energy is converted into heat energy by the infrared absorbing material, which causes the temperature of the sensitive element to rise. No need for cool, can work at room temperature, and low price, small size. The disadvantage is that the sensitivity is low, the observation distance is short, and the response speed is slow, which can meet the general needs.
    • Uncooled detectors have been developed since the 1990s, and in recent years, the technology has become more and more perfect, and the cost performance has exceeded the cooled detectors, making the infrared optical system, especially the long-wave infrared objective lens, more and more widely used in the civil field.
    • The uncooled objective lens generally has a large aperture, and in order to obtain low noise, the F-number is usually 1-2. And the requirements of the field of view are also increasingly developing to the large field of view.
Uncooled, long wave infrared lens

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 1700nm. 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.
SWIR Lens
  • Medium-Wave Infrared (MWIR) Lenses, Long Wave Infrared (LWIR) Lenses mainly collect the thermal radiation generated by the heat of the object, so it is also called thermal imaging. Thermal imaging technology has important applications in industrial, medical, military, security and other fields.
The relationship between radiation exitance and temperature

 

  • Thermal imaging is a completely passive imaging, good concealment, difficult to detect. In the case of insufficient light at night, the heat energy emitted by the target can be directly obtained to form thermal images, and the true sense of night vision can be realized. At the same time, due to the long wavelength and good penetration, all-weather monitoring can be achieved. The selection of infrared imaging band should take into account the detector, image quality, observation environment, target radiation and cost.
  • Medium-Wave Infrared (MWIR) Lenses, The medium wave infrared lens generally takes the object of high temperature as the observation object. For example, the engines of military equipment and the ignition points of forest fires will produce a lot of thermal radiation, and the energy peak of these radiation is in the medium wave wavelength. With the development of detector technology, the utilization rate of incident light is improved. Although the medium wave radiation of room temperature objects is less, the thermal image of room temperature objects can be obtained by the medium wave infrared imager. Moreover, the detector of medium-wave infrared is sensitive and generally adopts cooled type. Compared with long-wave infrared, the thermal imager of medium-wave infrared has better resolution and high temperature measurement accuracy. In some specific scenarios, such as high humidity, transmission is better than long-wave infrared, suitable for long-distance remote observation and monitoring.
  • The infrared radiation of room temperature objects is maximum at 8-14um, which is matched with long-wave infrared lenses, and thermal images can be obtained using ordinary detectors. For example, in the application of building inspection, the object temperature is close to the natural temperature, or higher, usually a long-wave infrared thermal imager is used. With the development of uncooled detectors, long wave infrared is more and more used in the civilian field, although the imaging details are worse than the medium wave thermal imager, but the price is lower, is currently the largest market share of infrared applications.
  • MWIR lenses occupy a distinctive niche, serving as windows into a realm between 3000 and 5000 nanometers (3µm to 5µm).
MWIR Lens
  • Long Wave Infrared LWIR Lenses work well in the long wave infrared wavelength range, from 8000 – 12000nm. An LWIR lens is an important component of LWIR thermal imaging and surveillance systems and these lenses are used in both industry and medicine.
LWIR Lens
  • Near Infrared NIR Lenses are ideal for use in the region 900 nm to 1700 nm, and may be used for focusing and expanding NIR lasers as well as for fiber optics. NIR spectroscopy and imaging is also key in some medical diagnostic techniques, as NIR Lenses can be used to determine both the concentration and oxygenation of hemoglobin in the brain or other tissue.
NIR Lens

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.

Manufacturing Capability

 

SWIR lens

MWIR lens

LWIR lens

NIR lens

Wavelength

0.9um-2.5um

3um-5um

8um-12um

0.9um-1.5um

Focal length

25mm

50mm

6mm

25

F/#

2.5

0.94

1

2

Sensor

2/3″

2/3″

1″

2/3″

FOV

25°

13°

128°

25°

SWIR Lens
MWIR Lens
LWIR Lens
NIR Lens
Germanium MWIR Lens
Germanium LWIR Lens

Applications of Infrared Lenses

Infrared lenses find extensive applications across diverse industries, playing vital roles in areas such as:

  • Medical Instrumentation: Infrared lenses are integral to thermal imaging and non-invasive diagnostics, aiding in the detection of abnormal temperature patterns to identify diseases and injuries. For example, equipped with MWIR or LWIR lenses, infrared thermal cameras detect surface temperature variations on the skin, assisting in diagnosing conditions like inflammation, circulatory issues, and cancerous growth. Moreover, they feature in endoscopic devices for minimally invasive medical procedures.
  • Life Sciences: Infrared lenses are indispensable in NIR spectroscopy and imaging, enabling precise focusing of NIR light for chemical analysis, pharmaceutical research, and food quality control purposes. They facilitate accurate measurements and analysis in various life science applications.
  • Security & Surveillance: Infrared lenses play crucial roles in night vision and thermal imaging for surveillance operations. SWIR lenses enhance visibility in low-light environments, making them ideal for military, law enforcement, and security applications. LWIR lenses are employed in thermal cameras to monitor critical infrastructure and detect intruders, even in challenging conditions such as smoke, fog, and darkness.
  • Defense: Particularly MWIR and LWIR lenses are fundamental components in infrared cameras utilized for long-range surveillance, target acquisition, and tracking in defense contexts. They enable high-performance thermal imaging, essential for identifying potential threats in adverse conditions. Additionally, SWIR imaging with infrared lenses aids in target recognition and identification.
Optics for Life Science, Optics in Life Science Applications, optical filters in life sciences
Life Science
Security & Surveillance
Medical
Aerospace & Defense

Custom IR Lens Options

Avantier’s capability in customizing IR lenses is characterized by a meticulous approach that encompasses material selection, lens design, coatings application, and advanced manufacturing processes. We excel in tailoring IR lenses to specific spectral ranges while ensuring high performance and reliability.

 

  • Custom Specifications: We can cater to lenses meeting specific customer requirements, ensuring that every lens is tailored precisely to the desired performance metrics and application needs.
  • Custom Lens: IR aspherical lenses, spherical lenses, cylindrical lenses, custom shape, etc
  • Material Selection: We carefully choose materials such as Zinc Selenide, Germanium, Sapphire, Silicon, Zinc Sulfide, and Chalcogenide, based on desired spectral characteristics.
  • Lens Design: Our optical engineers and specialized software create designs optimized for factors like aberrations, distortion, and thermal stability, achieving high resolution and efficient transmission.
  • Coatings: Custom coatings such as antireflection coatings ( AR coatings ) in visible, near-infrared, short-wave infrared, mid-wave infrared, long-wave infrared spectral ranges,  are applied to enhance performance, reduce reflections, and provide environmental protection, all while ensuring compatibility with the lens’s wavelength range and material.
  • Manufacturing Process: Utilizing precision techniques like machining and molding, we maintain strict quality control measures to deliver custom IR lenses with exceptional optical precision and consistency.

 

Our customized IR lenses stand as a testament to our commitment to excellence, offering cost effective and unparalleled performance tailored to your specific needs.

Stock – IR Lenses

We offer a wide selection of in-stock IR Lenses to meet your needs, including SWIR, LWIR, MWIR, and NIR lenses. These in-stock IR lenses excel in the realm of infrared applications and are invaluable in various industries. Avantier offers in-stock IR Lenses for sale, and also specializes in designing and manufacturing custom IR Lenses.

 

To find more information on Stock – IR lenses, visit our “Stock – IR Lenses” page.

Future Trends and Technologies

Based on the essential role of infrared lenses across industries and the ongoing evolution of technology, several future trends can be anticipated:

  • Enhanced Performance: Advancements in materials science and manufacturing techniques will likely lead to infrared lenses with improved optical properties, such as higher transmission efficiency and reduced aberrations, enabling more precise detection and analysis of infrared radiation.
  • Miniaturization: With the increasing demand for compact and portable infrared devices, there will likely be a trend towards the miniaturization of infrared lenses, enabling their integration into smaller and lighter instruments for applications such as wearable medical devices and unmanned aerial vehicles (UAVs).
  • Multi-Spectral Imaging: Future infrared lenses may incorporate multi-spectral imaging capabilities, allowing simultaneous capture of infrared radiation across multiple wavelengths. This capability can enable more comprehensive analysis in applications such as environmental monitoring, agricultural assessment, and defense reconnaissance.
  • Integration with AI and Machine Learning: As artificial intelligence (AI) and machine learning technologies continue to advance, infrared lenses may be integrated with intelligent algorithms to automate and optimize processes such as target recognition, anomaly detection, and image enhancement in surveillance and security applications.
  • Expanded Applications: As awareness of the benefits of infrared imaging grows, new and innovative applications for infrared lenses are likely to emerge across various industries, driving further demand for these critical components.

In summary, the future of infrared lenses is characterized by continuous advancements in performance, miniaturization, multi-spectral imaging capabilities, and expansion into new IR applications. These trends will further enhance our ability to harness the power of infrared radiation for a wide range of scientific, medical, industrial, and security purposes.

Related Content
WE CAN HELP YOU!

Contact us NOW for sales & expert advice.

Contact us
Request for quote