Infrared Lenses

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 customized optics, lenses, 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.

Structure of Lens

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 ragen 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

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.