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.
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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.
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.
© JOEL WOLFSON
A fantastic lens for normal visible light photography may be terrible for infrared (aka “IR”) photography. Choosing the right lens can be tricky. If you’re planning to get an infrared conversion for your camera, make sure you have lenses that will work well for it or be ready to buy one or more additional lenses, depending what you plan to shoot with your infrared camera.
Why is this true? Camera lenses are designed to be optimized for visible light so that they render as accurately as possible, how we see with our eyes. Infrared light is transmitted by lenses, but normally focuses on a different plane than the camera’s sensor.
Although digital camera sensors are capable of “seeing” infrared and ultraviolet parts of the spectrum, camera manufacturers put filters in front of the sensor that filter most of this out. When you get your camera converted to infrared, the conversion company replaces these filters with ones that allow the sensor to see a specific part of the infrared spectrum and may also include part of the visible spectrum. When you look at the choices offered, you can actually choose how much of the spectrum your converted camera will see. This offers a variety of looks from which you can choose. Because of the intricate and delicate nature of converting digital camera sensors for infrared, it is very important to choose a reputable and experienced conversion company.
See my Favorites page on my website for recommended conversion companies.
The most common issues or problems that show up with infrared that you won’t see in the same lens with visible light photography are “hot spots”, loss of acutance (sharpness), and sometimes excessive flare.
Hot spots are usually bright areas in the middle of the image and tend to get worse and more defined as you stop down. Some lenses don’t exhibit hot spots at all and thus are preferable for infrared. Or hot-spots may not appear at wider apertures but show up as you stop down (example below.) With zoom lenses you may get hot spots at some focal lengths and not others.
Something else I’ve noticed but isn’t widely reported is loss of acutance with the same lens compared to its visible light performance, especially as you go out from the center of the image. Because people use different terminology for resolution or acutance, for ease of explanation, let’s call is apparent sharpness. It is not always strictly how well the lens resolves that leads to loss of apparent sharpness. It can also be lack of contrast, other optical factors or a combination of these. For example, a subtle broad and gradual hot spot will cause a loss of apparent sharpness in the central area by reducing contrast there.
Many infrared shooters like the dreamy look of softer edges and don’t seek to have the same apparent sharpness they’d expect with visible light. With the infrared image that I used for my example below I had good success getting sharpness comparable to visible light using Topaz Sharpen AI. I don’t show the sharpened results here because I want viewers to be able to see the infrared versus visible light difference. However, with such amazing tools available to us, it can now be an artistic choice.
Finally, the flare issue is highly variable and dependent on the situation much like visible light. In my experience, some lenses may be more prone to flare using infrared than with visible light. For me it’s not a deal breaker if the lens is otherwise good for infrared. I treat it as I would with visible light: I try to avoid shooting directly into the sun or other light sources. For those times I want a sun star I just try it and see if I get excessive flare or not.
I’m rather compulsive about testing every lens I buy, both for visible light and infrared. There have been several times I’ve gone through 2 or 3 samples to get a really good one. I’ve got the visible light testing down as I’ve been doing that for decades. In recent years, I’ve figured out some good tests for infrared. Generally the number one issue is hot spots. With my studio being located in northern Arizona, more days than not, I have a clear blue north sky to shoot hot spot tests. I am able to test resolution using the same ISO targets as for visible light, in my studio. Because resolution can change with focus distance my studio test is limited to a practical range of about 3-18 feet (1-6 meters) so I will also do field tests to check lenses at greater distances. These are the controlled tests. I will also shoot various subjects in a less controlled way just to try different situations, sun angles, etc.
I have found that potential lens issues when shooting infrared are situational. By this I mean depending on the lighting, subject matter, and the specific conversion, issues with lenses may show up to a greater or lesser degree. For example, if you’re shooting a nature scene that has lots of trees in the center area of your image, you may not see a hot spot that might be visible if that same area was clear blue sky or with different lighting angles. Hot spots, in particular, can be more or less prevalent depending on the lighting. And typically hot spots are less noticeable with black and white. Generally hot spots are the worst with cameras converted to “pure” infrared in the 830nm-850nm range. So if you get a conversion with a lower number/frequency such as a 590nm, it is possible you may not have problems or as many problems with a given lens. Additionally you may encounter different results with a “full spectrum” conversion.
While it’s quite easy to find multiple reviews for any given lens, they rarely cover infrared performance. For this reason I have done a number of exacting tests myself on numerous lenses using infrared. In some cases I have sought out third party lenses when the manufacturer doesn’t have one in my desired focal length that works well in infrared. Sometimes I just end up buying a lens and trying it because I can’t find enough (or any) information about its infrared performance.
I have several recommendations (see My Recommended Lenses below) based on my tests and real world use. I’ve also included a resource section for tests done by others.
If you’re lucky, you find a lens that will work well for both visible light and infrared. For example the Sony 100-400mm f4-5.6 GM is stellar for both as long as you don’t try to use the 1.4X teleconverter for infrared. For a lot of my photography (both visible and infrared) I like to have a walkabout lens that covers a broad range of focal lengths so I don’t miss shots while changing lenses. For my Fuji system I keep the Fuji XF 18-135mm on my infrared body and the Fuji XF 16-80mm on my visible light body. The XF 18-135mm happens to be superb for infrared. In the case of the Sony full frame system, I really like the FE 24-240mm. It’s certainly less than perfect for infrared but the range is so handy I just try to avoid focal lengths and apertures that are troublesome. Though it isn’t ideal, with the overlap of the Sony/Zeiss 35mm f2.8 prime, 12-24mm, and 100-400mm I can cover most situations where the 24-240mm might fall short.
I’m including lenses I’ve formally tested as well as those I’ve found to work well for infrared but prior to implementing my more formal tesing. I’ve used all of them in real world shooting. The lenses I’ve formally tested are ones I purchased more recently for Fujifilm APS-C (XF mount) and Sony full frame (FE mount) cameras. My tests were done with 665nm conversions for both. I’ve also included a few lenses for Micro 4/3 using a 590nm converted camera, that I have found to work well in real world use.
Keep in mind that your results could be different, particularly with different camera models and IR conversions but this should be a good guideline. It is always best if you can try before you buy and if you can’t do that, then rent or make sure the store has a good return policy.
The list of lenses below are ones that range from partially useable to excellent for infrared. Please read the comments to guide you.
Note for the technically minded IR shooters: I think the 665nm conversion used in most of my tests is a useful one as it sits between the 590nm which tends to be more forgiving and the 830nm which tends to be more unforgiving regarding infrared issues.
Both formal testing and real world use for infrared:
IRLENS Product Page
Fujifilm X-Mount
Fujifilm XF 16-80mm f4 OIS (no hot spots wide open through f5.6 at 16-24mm. Good through f8 at 35mm. 50-80mm good at all apertures)
Fujifilm XF 18-135mm f3.5-5.6 OIS (good at all focal lengths and apertures)
Fujifilm XF 27mm f2.8 R WR 2nd gen (only useable at f2.8 no hot spot wide open but hot spot from f4-f16. More defined as you stop down. It is so well defined at the smallest apertures, it could be spotted out in many cases)
Fujifilm XF 55-200mm f3.5-4.8 OIS (good at larger apertures, hot-spots may show at f8 and smaller)
Fujifilm XF 70-300mm f4-5.6 OIS (best at apertures below f11 on the wider end and it gets better at 200-300mm)
Laowa 9mm f2.8 X-mount (no hotspots but sharpness falls off towards edges)
Zeiss Touit 12mm f2.8 X-mount (no hot spots wide open through f8, very subtle hot spot at f11)
Viltrox AF 56mm f1.4 X-mount (no hot spots wide open through f5.6 with f8 being quite usable most of the time)
Sony full frame E-mount
Sony FE 12-24mm f4 G (good from wide open through f8 at all focal lengths)
Sony Sonnar T* FE 35mm f2.8 (no hot spots wide open through f11.)
Sony FE 24-240mm f3.5-6.3 OSS (only good at some focal lengths and apertures but not others)
Sony FE 100-400mm f4.5-5.6 GM OSS (excellent overall but 1.4X teleconverter not recommended)
Sony APS-C E-mount
Sony E 18-135mm f3.5-5.6 OSS (My top choice for Sony APS-C. Excellent overall with no hot spots at any aperture and tested focal lengths)
Sony E 18-200mm f3.5-6.3 OSS LE (great for its absence of hotpsots at all apertures and focal lengths but only moderate performance for sharpness, as one might expect for this range. NOTE: Sony makes two other 18-200mm APS-C lenses. I only tested this one, not the PZ or older non-LE models )
Real world use for infrared but without formal testing:
Micro Four-Thirds
Olympus M.Zuiko Digital 12-40mm f2.8 PRO (no issues, even at smaller apertures. Sharp to edges and good sun stars)
Panasonic Lumix G Vario 100-300mm f4-5.6 ver 1 (hot spots at 100mm but does well above 180mm. This version 1 lens is discontinued but may be available used.)
Panasonic Lumix G Vario 14-45mm f3.5-5.6 (excellent throughout range of focal length and apertures. This lens is discontinued but you may find them used)
In addition to my testing that I’ve provided here, the links that follow are a decent starting point to further help you choose lenses. One of the links is specific to Fujifilm X-mount lenses. The other two include several brands. For the most part they are all geared towards hot-spot performance. Simon Weir’s tests (Fuji mount only) provides some comments on sharpness too.
I recommend reading the notes and details for each of the lists.
Kolari Vision hotspot database This is a compilation database they put together of numerous major equipment brands and various third party lenses.
LifePixel hot spot testing database The testing was done by LifePixel themselves, of various Canon, Nikon, Fujifilm, and Sony lenses
Simon Weir’s tests of Fujifilm (XF) mount lenses A useful resource for Fuji shooters. He has information for both hot spots and sharpness
In the end, shooting infrared comes down to aesthetics and your personal preferences. Hot spots can be annoying but soft edges and/or a hazy feel are often considered part of the charm of infrared photography, especially in black and white. My aim for this article is to arm you with enough information to make informed choices based on the way you shoot or intend to shoot while participating in the amazing world of infrared photography.
**To see more of my infrared photography go to my Infrared and Latest galleries on my website!
Happy Shooting,
Joel
Joel Wolfson is an internationally published photographer that loves teaching as much as shooting. He shares his 35+ years of experience as a working pro with other photographers by way of his custom workshops, 1 on 1 training, articles, blog and speaking engagements. His goal is to make learning and improving one’s photography easy, fun and rewarding. His articles have been translated for use in more than 30 countries yet he is best known for his artistic images of fleeting moments and unexpected views of everyday places around the globe.
He is one of the pioneers of digital photography. Joel has presented at national conferences, written articles for global publication, and conducted digital photography seminars for Apple and other corporations starting in the early 90s. His roster of notable clients has included Newsweek, Elle, Seventeen, Houghton Mifflin, Arizona Highways, and corporate clients such as AT&T, 3M, United Airlines, Chase and Pillsbury.