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.
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.
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.
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:
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.
This is the tried-and-true classic IR filter. It allows for some great blue sky false color and provides great contrast and dynamic range for black and white. This is equivalent to the Hoya R72 and Wratten 89b.
When to use this filter: This filter is good if you are interested in shooting some mild color and black and white. This filter produces the traditional dark blue skies and can also be processed for color.
While not as high contrast as the 850nm, people prefer this filter over the 850nm for B&W work, as it allows a little more color for B&W processing. This filter requires post-processing and is compatible with a full spectrum camera or a lower cutoff IR converted camera. This filter can also be used with stock cameras with a long exposure.
This filter is suitable for a dedicated black and white infrared camera. It will produce bright whites and pronounced darks. With a custom white balance in camera, the picture is close to pure B&W without any processing. Equivalent to the Wratten 87c.
When to use this filter: This filter is the best for the highest contrast B&W, resembling traditional B&W IR film. Also good for forensics and other applications where the deep IR wavelengths are helpful. This filter is compatible with a full spectrum camera or a lower cutoff IR converted camera. This filter can also be used with some stock cameras with a long exposure.
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The first thing to consider is whether you will shoot color or not.
If you plan to shoot only B&W, then the 850nm filter is the best choice. If you plan to shoot color even occasionally, you should go with the 720nm ir filter or below.
When choosing between 590nm, 665nm, and 720nm, the first consideration is your aesthetic preference. If you like the yellow leaf effect, you should choose the 590nm or 665nm option. If you want to shoot regular color shots with white leaves and blue skies, then the 720nm ir filter is probably right for you.
With these enhanced color filters, you will have an increased color range to work with. With processing, it is possible to desaturate photos from these two filters to look like the 720nm image.
This adds more flexibility when shooting and allows for good color results in some shooting situations that would not work so well with the standard 720nm filter.
Some cameras don’t have very good color results with the 720nm filter, such as the Nikon and some Canon PowerShots, but the 665nm filter can overcome this.
Another nice benefit of these filters is that you can use higher cutoff IR filters over them.
For example, with a 665nm conversion, you could use a 720nm or 850nm and still take handheld pictures that will look exactly like the higher cutoff filter.
However, you couldn’t use a lower filter, like the 590nm filter. If the camera you are converting has live view, this is an easy way to take advantage of both the color and B&W aspects of IR.
A downside to these two filters is that they have less contrast for B&W images.
These filters can be more unpredictable, yielding different results depending on the camera model and shooting conditions.
Cameras will also have a harder time setting a white balance with the enhanced color filters.
Another thing to watch out for is that the 590nm and 665nm filters can be a little less sharp than the 720nm and 850nm filters. Since they let in a broader light spectrum, there are more chromatic aberrations and a bit softer focus.
The replacement filters on most compact cameras need to be very thin and leak more visible light, so 590nm, 665nm, and 720nm filters can produce duller color.
The 850nm filter will also leak a little visible light. They will still be monochromatic but may be red or blue-tinged and require processing.
A custom white balance is crucial to achieving a good false color effect with the 590nm and 665nm filters. You should only order these filters if your camera has a custom white balance option.
Keep in mind that just because your camera has a custom white balance setting does not guarantee that you can achieve images like those above with these filters.
Camera white balances were not made to work in infrared, and the camera may not be able to measure a white balance correctly, leaving you with unexpected results. 590nm filters have the most trouble with this.
If your camera does not have a custom white balance option, the 850nm filter still works for B&W photography. The 720nm filter can still be used to get good false color results even with auto white balance, although the results are not quite as reliable.
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