Search the Community

There's two types of upconversion phosphors: the "direct" ones, that absorb multiple low-energy photons to emit one higher-energy photon, and the "storage" ones, that must be charged with high-energy light (such as UV) and release their stored energy as photons when illuminated by IR light. MaxMax sells both, and below is a video of a comparison between two storage phosphors: What I noticed is how bright they are. The laser pointer used in the video is probably also quite powerful, but direct upconversion phosphors are very inefficient. [Edit: in the comments the author of the video says the laser is 980 nm, 100 mW] Andy has experimented with them (read this topic), and he can tell you he needed a lot of light. Of course the problem is that these phosphors need to be charged. If one wants to take video, then one way is to flash the phosphor in the blind times between frames, somehow synchronizing the flashes with the camera sensor (or maybe even continuously illuminating the phosphor and imaging it through a longpass filter that blocks the charging light). The storage phosphors sold by MaxMax (in the video above) are rated to respond between 700 and 1500 nm. To my knowledge, this techique hasn't been tried yet.

https://medium.com/valence-digital-magazine/say-hello-to-the-worlds-first-handheld-swir-camera-c5432b3a0f3f https://www.ebay.com/itm/800-1600nm-Handheld-SWIR-Smartphone-Compatible-Camera/113858109409?hash=item1a8278dfe1:g:WhEAAOSwRsRdWbbT 128x128 resolution When they hit 320x240 or whatever, I may want one...the TriWave is nice but not portable at all. Incidentally, the website falsely claims that nobody has used germanium for SWIR, when as we know, the TriWave does. I would very much like to know what is going on here. Is there a relationship between the former NoblePeak and Stratio, who makes this new camera?

Several of these on eBay, priced between about $1,200 and $1,700. All from China, apparently from different vendors (although they may be related). Resolution should be 320x256. Example: https://www.ebay.it/itm/304980132465?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=fcdsnphwro-&sssrc=4429486&ssuid=kmqj_e1bqvo&var=&widget_ver=artemis&media=COPY

I finally figured out all the settings with my InGaAs linescan camera setup. Here are the first photos. Most of them full InGaAs spectrum, I still don't have my 1575nm bandpass filter - it should look even nicer with a filter. I used a VIS Nikon 50mm lens.. A proper SWIR lens wouldn't make big difference regarding the resolution, especially with the bandpass filter. The VIS lens has however only 40% average transmission in SWIR. Landscape SWIR 800-1700nm VIS (400-800nm for comparison) The next is isopropanol and water (800-1700nm) VIS (400-800nm) Another mountain SWIR (800-1700nm) SWIR with uncoated silicon wafer filter (ca. 1100-1700nm) VIS (400-800nm) VIS full spectrum (400-1200nm) with my ASI294MM (monochrome CMOS) and 50mm lens And finally ASI294MM with 860nm longpass (860-1200nm) I still like this last photo the most, but I'm very excited to discover more SWIR . :)

I do not remember seeing anything here about this camera: https://trieye.tech/ovi/ I just found it in a newsletter for optical components and know nothing more about it.

My interest in light didn't end when I studied laser physics in Hungary and didn't start in the UK while developing high power lasers. I'm now in Switzerland focused on the infrared part of the spectrum, NIR, SWIR, hyperspectral, multispectral. Continously collecting light: line and area scan cameras, optical simulations, spectrometers, slit goggles.. I'm DIY-optics (dot com) himself. ;) You have a very nice community here, I appreciate being a new member. Hello Everyone

I finally redid my pano today, thanks to the overcast weather. (Link to previous attempt) When the sun is out, my mere 10 bits of dynamic range are not enough to capture everything in the photo. It becomes like trying to photograph the moon AND the stars simultaneously -- pick one! Even so, there was enough variation in the photo that I had some trouble stitching the bottom edge with all that black snow. The snow seemed much darker today, which is probably a sign of the thaw, since it was well above 0 deg C. Details are the same as the last attempt except that I stitched in Hugin. Visible (today) Previous pano for comparison purposes. We have had additional snow + melting in the interim.

SAFETY WARNING: UV-C is dangerous to your eyes and your skin. UVP DOES NOT SUPPORT USING UV-C ILLUMINATION. [UV SAFETY] UV-C Light Dangers A short YouTube video that includes a 254 nm clip: https://youtu.be/CaXzgumCn34. The gear they use is interesting.

Don't get too excited. Despite the grand title, the results are a little disappointing. Part of this is the fault of my equipment being insufficient for the job, but a lot of it is apparently the moon's fault. It just doesn't vary that much with wavelength, seemingly! But a negative result is still a result as they say, so here you are... Equipment -TriWave camera (germanium-on-CMOS sensor), which has sensitivity from 350-1600nm -Thorlabs 1" 100mm mounted achromatic doublet lens, AR-coated for 1050-1700nm -Thorlabs SM1 Lever-actuated Iris Diaphragm (for controlling aperture) -Thorlabs Filter Mount with Sliding Modular Inserts (with a bunch of the inserts for holding my filters. These are very convenient. You slide the filters back and forth for quick swaps.) -Various Thorlabs SM1 tubes and C-mount adaptors for hooking things together and holding them at the correct distance. -The filters are a mix of Omega seconds from eBay for NIR, and high quality Thorlabs filters in the SWIR (1200nm+). -INOGENI USB 3.0 NTSC video capture card (because the TriWave is analog output) Software - Custom written MATLAB code for snapping bursts of images and saving them - Lynkeos astronomy software for aligning images and weeding out low quality ones - Photoshop Resolution was severely limited by the optics in this case, although the TriWave is only 640x480. I was using only about 128x128px of that, however, due to the 100mm lens. If I get a longer lens, I may try again with higher resolution. Each of these individual images is boiled down from a stack of 600 photos each, but the Lynkeos software throws out many of the bad frames before the rest are averaged together.

Same settings and equipment as the other flowers in this series, with exceptions noted below. UV 2mm UG11 + 1.75mm S8612 (Convoy S2+) Saturation strongly increased Visible BG38 2mm and DB850 filter (645-405nm) NIR-Red-Green (550-645nm + 835-875nm) Tiffen#12 + DB850 filter, and my usual algorithm for making the IRG, described in the DB850 filter thread NIR Hoya R72 + DB850 filter (835-875nm) SWIR (1500-1600nm, made by the panorama method and reduced for higher resolution) UVIVF under Convoy S2+ and using BG38 2mm and DB850 filters --- Comments: The SWIR looks a lot like the visible but with a lighter disk in this one, enough that I got scared and decided to check if my filter was leaking. However when I stacked it with my hard-coated premium Thorlabs 1200nm long pass (guaranteed >OD5), it looked the same, so I guess it just looks similar by coincidence. If you look at the bottom left of the flower, there is a tiny splash of water on a petal, so you can see that the water, although dark, isn't inky when it's just a thin layer like that. This morning the disk florets had started to open up, and they are white in the SWIR 1500-1600nm band:

The new Sony SWIR sensor looks really interesting. Capable from at least 400nm to 1700nm. For only about $9000 USD, you can buy one. First saw it here: http://image-sensors-world.blogspot.com/2020/05/sony-unveils-swir-sensors-for.html?m=1 Here is the Sony data and prices: https://www.sony.net/SonyInfo/News/Press/202005/20-036E/

Is it a metaphor, or just water drying in SWIR? You decide! 1450nm, water on paper. https://youtube.com/zC5et6slLCQ

"Silicon inspection uses next-generation SWIR cameras" https://www.laserfocusworld.com/detectors-imaging/article/14196038/silicon-inspection-uses-nextgeneration-swir-cameras?utm_source=LFW+Detectors&utm_medium=email&utm_campaign=CPS210224014&o_eid=1758A2788401D4U&rdx.ident%5Bpull%5D=omeda%7C1758A2788401D4U&oly_enc_id=1758A2788401D4U This is the kind of equipment we may hope to find on the second-hand market in maybe 5 to 10 years.

After a great deal of work, I have figured out how to access the video feed from my TriWave in MATLAB, and I've written a program to capture time lapses and process the resulting frames. Each frame of video is actually 120 frames from the camera (4 seconds' worth) averaged together, and this is repeated once a minute. This video took 90 minutes in real life, but's 13 seconds of video, or about 415 times faster than reality. Lens: Wollensak Velostigmat 25mm/1.4 Filter: Thorlabs FB1450-12 (1450nm, 12nm FWHM) https://youtube.com/dEgNbJj6NWU YouTube's compression really degrades it. ---- Update: I repeated the experiment at 1250nm. For some reason the Triwave is significantly less sensitive at 1250nm. (Or my lens has lower transmission that at 1450nm? Unlikely.) I don't THINK it's the filter, since the peak transmission is 50%-ish for the 1250nm but 30%-ish for the 1450nm, and the bandwidth is almost the same. ANYway, excuse my noise. Filter: Thorlabs FB1250-10. https://youtube.com/Br3hr_6Z7Tc

As previously discussed, ice and water have different spectra in SWIR. You can see this pretty graphically demonstrated when you watch a snowflake melt. https://youtube.com/5zNsfJMPaHg https://youtube.com/kzp6lH52hW8

Here's a tricolor of snow on a window. The filters are: 780BP30 - red channel 1064BP25 - green channel 1500 long pass (but probably 1500-1550 effectively because of the camera gain fall off) - blue channel The color channels are BGR essentially because it made the snow stand out better. Alternative is to have magenta cyan snow in RGB. visible: Individual frames: 780nm ("red") 1064nm ("green") 1500nm ("blue")

Consider this a first attempt, which I plan to update or replace tomorrow when it's light out again. I started a SWIR pano of the snowy landscape out my window but unfortunately the sun set before I could finish. Oh well. In addition to missing data, there are some obvious places where the lighting changed between captures. I will try again! Equipment TriWave Ge-CMOS sensor camera Wollensak Velostigmat 25mm lens (but the camera has a 1/2" sensor, so there is a huge crop factor of around 5.4, so the effective focal length is about 135mm) 1500nm long pass filter from Thorlabs Tripod Software TriWave driver software (seems to be custom coded for this particular camera -- I definitely think my camera must have been a prototype) Custom MATLAB script to batch process the images and prepare them for the panorama, including subtracting off fixed pattern noise from the sensor Photoshop CS6 SmartDeblur for deconvolving the image to sharpen it Observations - ice and water have different absorption curves and it's definitely possible to distinguish wet snow (black areas near windows and on the ground) from well-frozen snow (the gray on the roofs). ETA: it seems ice absorbs more light than water at 1500nm, not less, so my updated hypothesis is that the contrast is due to less scattering between ice/water interfaces than between ice/air interfaces. See discussion below. - brick has gorgeous patterns in SWIR

I saw this on eBay: https://www.ebay.co.uk/itm/333795972392 It is a SWIR camera which is "non functioning and for replacement parts" (translated from Italian, this may not be how the message appears in English). I think there is everything except the lens, maybe someone could be able to repair it and make it work? What do you think?

A friend (who I am hoping to entice to join the forum one of these days) sent me a link to this company, which seeks to make some kind of low-cost SWIR using CMOS(!) of all things. https://trieye.tech/products/

I have had occasion to notice that a number of flowers start to show colors again in SWIR, and it turns out that the tiny flowers (florets?? I don't have the vocabulary down, although I'm sure Birna could help) on Queen Anne's Lace have dark centers at 1500nm. The darkening starts before then and is visible also in the longer wavelength parts of NIR. Using the TriWave (which has a germanium-on-silicon sensor with range 350-1600nm), I made the following "true color" IR image from two Omega bandpass filters and a Thorlabs longpass (but effectively a bandpass since it's at the end of my sensor's range of 1600nm). - 1500nm hard coated premium edgepass from Thorlabs (blocked OD5+ through 200nm, which is rather important with the Triwave since it's much more sensitive in visible than at 1500nm+). - 1064BP25 Omega - 780BP30 Omega These were placed in the R, G, and B channels respectively to produce the following image: The image has been processed by registration of the channels, contrast adjustment, noise reduction, sharpening, and boosting saturation. Original images: 1500nm-1600nm (but probably mostly 1500-1550nm because the TriWave's gain falls quickly in that range): 1064nm: 780nm: This result is startling given that in visible and in UV, the flower shows a uniform light or dark appearance, with the flower centers undistinguished from the petals. VIsible: UV (S8612 1.75mm + UG11 2mm): -- Edited to add a large pano of the whole head at 1500nm. 58 images.

When reading about Sony Exmor sensors I stumbled upon it's 4th generation Exmor sensors claiming to have enhanced infrared sensitivity because of deeper pixel well depth. In fact there are for sale infrared CMOS camera's that can detect in range of 400-1700nm although SWIR sensiivity is low but it's not at least some exotic technology.

A classic sunflower. The SWIR is the major contribution here, because many sunflowers have been imaged before on this forum. I made a 530 image panorama to get adequate resolution, and the results look nice. It took all night to stitch the images, and I went through 5 software packages before I found one that didn't get bogged down by the sheer number of images involved. Most stitching programs are geared toward a small number of images with a large number of pixels, rather than the opposite situation, which is what I have with the TriWave! Vis sunshine Resolve 60mm lens, F8 iso640 0.04" (DB850+S8612 1.75mm) UV sunshine Resolve 60mm lens, F8 iso2500 2" Vis sunshine Resolve 60mm lens, F8 iso640 0.04" (DB850+S8612 1.75mm) UV sunshine Resolve 60mm lens, F8 iso2500 2" UVIVF ConvoyS2+ Sony FE 55mm lens, F8 iso1000 30" IRG sunshine Resolve 60mm lens, F8 iso400 0.005" (DB850+Tiffen #12) Near infrared (830-870nm) sunshine Resolve 60mm lens, F8 iso400 0.05" (DB850+Hoya R72) SWIR (1500-1600nm) halogen Thorlabs 50mm achromatic doublet, F10-ish, not sure how to quantify the rest of the exposure info. Thorlabs 1500nm long pass filter. 534 image panorama stitched with Panorama Stitcher, a Mac app available in the Mac App Store. This was the program that finally worked after trying Hugin, PTGui, Photoshop CS6, Panoweaver, and Autopano Giga. Autopano Giga's free trial actually worked, but when I went to buy it, I discovered that Kolor, the company that made it, had been bought by GOPro, which then discontinued the product! With no way to unlock the software, I had to find another program. Due to stitching errors near the edges, I was forced to crop this more than I would have liked. The results are still pretty nice, though, and I found that the sunflower (as with other members of the aster family) has a dark center in the SWIR 1500-1600nm band, despite being pretty uniformly white in the 850nm NIR range.

Stefano's thread on solar panels glowing in IR (when you push current through them the "wrong way" rather than shine light on them) occasioned some skepticism from me (since indirect bandgap semiconductors are supposed to make very poor LEDs). It seems that "very poor" is not the same is "you don't get anything at all" because I can reproduce the effect. The equipment was: -TriWave germanium-on-CMOS camera (QE >0 between 350nm and 1600nm, roughly) -Solar panel I ripped out of an old IKEA solar powered lamp -9V battery and alligator clips -1100nm, 1150nm, 1200nm, and 1500nm long pass filters (all from ThorLabs). The first two are blocked to OD4+, the latter two are blocked to OD5+. - f=100mm NIR-AR-coated Thorlabs lens (25mm diameter) The results were as follows. With no filter on the camera at all, and power applied to the solar panel: With the 1100nm long pass: With the 1150nm long pass: I didn't continue on to the 1200 and 1500nm long pass since I'd already lost the signal at this point. It seems pretty clear that most of the signal is below 1150nm (regardless of what graphs on the internet might say...). I put my 980BP10 filter (Thorlabs, naturally, one day I will own their whole catalog and die happy) on the Sony A7S and took a photo: EL-Nikkor 80mm/5.6 F/5.6, ISO10000, 5 min exposure (bulb) Still to try: putting the 1100nm long pass and the 1150nm long pass on my Sony and seeing what I get.

STICKY LIST Sticky :: SWIR Photography: Cams, Mods, Lenses, Lights, Links (You are here.) Sticky :: UV-Capable Lenses Sticky :: UV/IR Books Sticky :: UV/Vis/IR Filters Sticky :: UV Induced Visible Fluorescence Sticky :: UV Photography: Cams, Mods, Lights, Links Sticky :: White Balance in UV/IR Photography Sticky :: IR Photography: Cams, Mods, Lenses, Lights, Links by Andy Perrin for UltravioletPhotography.com Started: 28 June 2019 Edited: 26 November 2020 Note from the author: To paraphrase Andrea, "This is a joint effort by the members who enjoy [shortwave] Infrared photography. Thanks to everyone for their suggestions, comments, proofreading, lists, links, measurements, experiments and all round good fellowship." Please PM Andy Perrin on UltravioletPhotography.com with any corrections, additions or suggestions. Abbreviations: IR = infrared (taken here to mean the entire band from NIR-LWIR) UV = ultraviolet NIR = near infrared SWIR = shortwave infrared MWIR = mediumwave or midwave infrared LWIR = longwave infrared Quoted prices are in US dollars and are only meant to give a rough idea. INTRODUCTION As another well-known Guide once put it, the infrared is big. It is, in fact, so hugely mind-bogglingly big that it can't be properly treated as a single band for many purposes. It has thus been divided into a handful of sub-bands according to several different mutually inconsistent schema. Wikipedia (as of June 28, 2019) lists five different schemes to divide up the infrared, several of them with overlapping nomenclature for different wavelength cutoffs to add to the confusion. For this guide, we will use the scheme termed "Sensor response division scheme" on Wikipedia, which starts with Near-Infrared (NIR) from 700nm-1000nm, which is where silicon sensors cut off, followed by Shortwave-Infrared (SWIR) from 1000nm to 3000nm, Midwave-Infrared (MWIR) from 3000-5000nm, Longwave-infrared (LWIR) from 8000-12000 microns or 7000-14000 microns, and then Very-long wave infrared from 12000-30000 microns. The interested reader can consult Wikipedia for the other schema, while the alert reader is left to ponder what became of the gap from 5000-8000nm. Unfortunately, this mess has real consequences for those trying to purchase shortwave infrared camera equipment because it may not be listed as "shortwave infrared" on eBay or other sites. Equipment may be listed by the type of sensor it is compatible with, usually InGaAs, or as SWIR, shortwave, the generic "IR," or even NIR (which is sometimes considered to include as far out as 5 microns!) The searcher is advised to try variants on all of these or else miss out on deals. SHORTWAVE INFRARED PHOTOGRAPHY SWIR CAMERAS Using the classification above, SWIR starts at 1000nm. Silicon still has some sensitivity in the 1000-1100nm region, and for this part of the band one can use an ordinary converted silicon camera. However, while some interesting SWIR effects start here, such as water becoming light-absorbent, most of the differences from NIR don't become significant until one is past 1100nm. Silicon sensors can be made to exhibit some sensitivity to SWIR from 1460-1600nm by coating them in an up-converting phosphor material. These coated sensors use the anti-Stokes effect, in which two SWIR photons hit the material and a single NIR photon is emitted, which is then captured by the silicon sensor. Edmund Optics sells these. They are intended for calibrating telecom lasers, and have not been tested for imaging purposes. Typical new cost is the $2000-3000 range. The author cautiously warns against purchasing one, unless you find a really outstanding deal, for reasons described below. A second (bad) option is to use an up-converting phosphor screen in conjunction with a converted silicon camera. The screens are available from Edmund and also under other brand names for much less than Edmund's. The author purchased one of these on eBay for ~$200 and did a series of experiments with them. In these experiments, it was found that the phosphor material is extremely weak, rendering the apparatus as a whole quite insensitive. Thus it was necessary to use a very intense light source, nearly to the point of setting fire to the scene. In addition, the screen itself was granular and did not provide good resolution or contrast. Because the same phosphor materials are involved in the coated sensors of the last paragraph, the author doubts that the coated sensors will work well for general purpose photography. However someone would need to acquire one to test the hypothesis — a lot of money for something expected not to work well. A relatively low-cost option that would provide SWIR coverage up to 1550nm is the Find-R-Scope vidicon tubes. These are analog devices, but could potentially be coupled to an ordinary camera. They are relatively easy to find on eBay for prices under $1000. Buyer beware — not all of them go out to 1550nm. Read listings carefully, and if it does not say it is 1550nm-capable, assume it is not. Vidicon tubes are rated only for a certain number of hours before they wear out, so the age of the device may also be a consideration. The author has not tested any of these, but this may be the most cost effective entry into SWIR. The next step up in quality from the vidicon tube imagers is the most traditional means of SWIR imaging: Indium Gallium Arsenide (InGaAs) cameras. These are usually digital cameras with resolution of 320x240 or 640x480 (and higher now, but at a cost) with excellent sensitivity from 900nm-1700nm. The cameras are generally machine vision cameras for industrial, medical, art conservation, or espionage use, so they need to be attached to a computer to take and store the photos. Conceivably some kind of portable apparatus could be rigged up by using a tablet as the computer. eBay price is generally $5000-$10000, but I have seen as low as $3000. Typical brand names are Goodrich Sensors Unlimited, FLIR Tau SWIR, Allied Vision, and Princeton Instruments (far from an exhaustive list). Good questions to ask of a seller include whether the camera has a lens, whether it has the driver software needed to run, and if it comes with a power supply. NOTE: Beware of line scan cameras, which capture only a single line of pixels rather than an image, with the intent that the object or camera motion is required to digitize a picture. These are frequently available on eBay for much cheaper than normal cameras, making them look like a tempting bargain. Avoid the temptation. A rarely seen alternative to InGaAs is the Germanium-on-CMOS imagers made by the defunct NoblePeak Technologies company. These cameras, collectively called the TriWave, ranged from 320x240 up to some higher resolution limit unknown to this author. The cameras are sensitive from 300-1600nm. A high resolution example was demonstrated by Nick Spiker on this forum here. The author owns an analog-output 640x480 version and paid $3000 for the camera in "new-unused-but-opened" condition (still in original plastic bags) with all accessories except the lens. The TriWave cameras were in active development at the time of the company's demise, and therefore it is likely that all the TriWave cameras have slightly different capabilities, depending on what point in the development cycle they were sold at. Later cameras probably had digital output via a USB port, as shown in TriWave datasheets. These cameras are cooled by a built-in thermoelectric cooling system and require about 60 seconds to "boot up" while you wait for the chip to reach -80C. The camera will not produce an image until it reaches -70C or so, with optimal results at -80C or lower. As with InGaAs, when buying used ask whether the camera has its original lens, whether it has the driver software needed to run, and if it comes with a power supply. (Updated Dec 15, 2019) A new germanium camera is available as of late 2019 called the BeyonSense 1 with 128x128 pixels in a portable BlueTooth camera format that works in conjunction with a phone app for Android or iOS. The app for iOS was confirmed to be in the iOS App Store as of Dec 14th, 2019, and the camera itself was being sold on eBay for $1138. While the sensor is currently low resolution, it is hoped that future versions will improve on this and make SWIR more accessible. A new option by the company SWIR Vision Systems are the Acuros quantum dot cameras, which are quite high resolution, ranging from 640x512 up to 1920x1080 pixels as of 6/28/2019. The company claims the price is lower than InGaAs, but the author does not know the actual prices, which are not posted. Because the technology is new there are no used cameras available yet. The sensor seems to be particularly sensitive on the blue end of the visible spectrum (with unknown but likely high UV sensitivity) based on their published quantum efficiency chart. The sensitivity goes to zero by 1700nm. The cameras are digital machine vision cameras, so need a computer to operate like the InGaAs and Ge-CMOS cameras. SWIR FILTERS For all of the above cameras, appropriate filtration is necessary to block non-SWIR wavelengths and to narrow the piece of the SWIR spectrum the photographer wishes to look at. It is worth noting that some material properties can change significantly with wavelength in SWIR, so the 1000-1100nm band is different from 1200-1300nm, which is different from 1500-1600nm in terms of what one will see. In particular, sugar and water both have rapid variation across SWIR, so objects of biological origin like flowers or people are likely to show interesting effects. Depending on the type of imager technology, different levels of blocking will be needed depending on sensor. InGaAs, in particular, is not sensitive below 900nm, so does not require any visible light blocking or UV blocking. The Triwave Ge-CMOS camera, on the other hand, is sensitive from 300nm-1600nm, which means 300nm-1100nm (or higher) needs to be blocked well to see any SWIR. The photographer will need to evaluate their blocking needs based on what camera they are using, and what light source. The two best-priced options that the author has identified so far are Thorlabs and Omega Optical (in particular Omega's eBay site for out-of-spec filters is full of good deals). The author owns two SWIR Thorlabs filters, an FEL1500 (1500nm long pass), and an FELH1200 (1200nm premium long pass) and has noticed no out-of-band signals using the light sources available for testing with. In particular, visible contamination is a worry with the author's TriWave camera, but using the FEL1500, objects that reflect visible and NIR light extremely well but 1500nm SWIR poorly (e.g. human skin) show as black, indicating no contamination. For the 1400-1600nm band, the author feels the "skin test" is an easy way to check for poor filter blocking, much as dandelions are used to check for NIR leaks in UV. Note that skin is not dark in SWIR until 1400nm or so, so this is not a useful test in the 1000-1400nm range. Unfortunately, the author does not know of any SWIR absorption glass filters available for sale except the 1000nm longpass kind, which leak a bit of NIR. SWIR LENSES The lens situation in SWIR is similar to UV and the issues are the same. Most ordinary lenses will pass at least a bit of SWIR, sometimes as much as 50%. Multicoated lenses and lenses with many elements are bad news. Chromatic aberration and focal shift can cause problems. Because of the similarity in the underlying issues, UV-capable lenses probably make good candidates for SWIR testing also. One catch is that most SWIR cameras use C-mount lenses, so it will be necessary to use an adapter if one can be found. Another issue to keep in mind is that focal lengths are given in absolute numbers, but most SWIR cameras have tiny "cropped" sensors, so a 50mm lens on a TriWave with a 1/2" sensor, which has a crop factor of 5.4 relative to a 35mm sensor, will behave with an effective focal length of 50*5.4 = 270mm! An alternative to accidental SWIR lenses is to buy a lens intended for SWIR imaging. These use special glass types that pass SWIR better than ordinary lens glass, and they have broadband anti-reflective (BBAR) coatings designed for the SWIR region. The author has tried two of these. The first is a simple 50mm achromatic doublet from Thorlabs, which was purchased on eBay for less than the list price. The photographer is advised to always check eBay for Thorlabs equipment first, by entering the desired model number directly into the search box, because many bargains are available. Thorlabs also sells SM1 to C-mount adapters. Another lens tried by the author is a 12.5mm/F1.4 Kowa SWIR lens, also purchased on eBay, which was found to perform significantly better than the doublet in sharpness and contrast, even on a 640x480 sensor. While the Thorlabs lens was much cheaper, the Kowa's performance was so much better that it is the recommended lens of the two. On the TriWave, this 12.5mm lens has an effective focal length of 67.5mm, so it performs as a telephoto, not a wide-angle as one might naively expect. SWIR LIGHTING First, there is natural lighting. The sun produces abundant SWIR light. A very interesting effect is that the clear night sky also produces SWIR, via an effect called airglow, which is emission by chemical reactions in the atmosphere. The author has not been able to detect this effect yet, possibly due to light pollution. For artificial lighting, any incandescent source should work. Halogen lights are well-known to produce abundant SWIR. Unfortunately for SWIR photographers, while halogen room lights and desk lamps are still abundant at the time of writing (mid-2019), already it is clear that LED lights, which are more energy efficient and less likely to start fires, are dominating the market. In several more years, halogen lamps may become specialist items with expected price increases. SWIR LEDs and laser diodes exist but are expensive. Thorlabs sells the parts. The author has no experience with these, nor is he aware of any torches for sale. (Updated Dec 19, 2019) Another option is the Arcadia Reptile ‘Deep Heat Projector’ which has a steeply rising output in the range 1000-2000nm. If uneven spectral distribution is not an issue, this might be a possibiity. SWIR LINKS CAMERAS Phosphor/Silicon: Phosphor-coated CMOS camera from Edmund (not recommended, quite insensitive) Another phosphor-coated CMOS camera from Edmund (not recommended, quite insensitive) Vidicon Tube: Find-R-Scope from Edmund (less pricey than InGaAs or Ge-CMOS but has limited life) These can generally be found much more cheaply on eBay. Be careful, not all go to 1550nm. InGaAs: The traditional SWIR imager, excellent sensitivity, pricey, requires lens, power supply and software driver. Goodrich Sensors Unlimited FLIR Tau SWIR Allied Vision Princeton Instruments NOTE: Beware of line scan cameras, which capture only a single line of pixels rather than an image, with the intent that the object or camera motion is required to digitize a picture. These are frequently available on eBay for much cheaper than normal cameras, making them look like a tempting bargain. Avoid the temptation. Ge-CMOS: Excellent sensitivity, expensive, might be difficult to find. TriWave Unknown company, prototype product (although versions were seen on eBay), unknown sensitivity. BeyonSense 1 Quantum Dot: The most recent SWIR imager, high resolution, not much known yet about these. SWIR Vision Systems SWIR FILTERS Thorlabs filters Omega Optical Filters Omega eBay site for out-of-spec or batch over-run filters SWIR LENSES - Check eBay first for used copies, always. - Remember to account for the crop factor of your sensor when choosing focal length. - Keep in mind that it can be hard to find step rings for certain filter diameters. Designed for SWIR: Thorlabs Achromatic Doublets Kowa SWIR lenses Accidental SWIR Lenses: Wollensak 1 inch 1.5 Cine Velostigmat C mount (suggested by dabateman; tested by Andy Perrin)

I found this interesting: http://image-sensors-world.blogspot.com/2019/10/iedm-2019-sony-presents-48mp-all-pixel.html?m=1 In that article, Sony described a new high resolution SWIR sensor using Copper wiring to improve signal. Apparently, SWIR are becoming more popular. This is the quote: "Sony Semiconductor Solutions Corporation We developed a back-illuminated InGaAs image sensor with 1280 x 1040 pixels at 5-um pitch by using Cu-Cu hybridization connecting different materials, a III-V InGaAs/InP of photodiode array, and a silicon readout integrated circuit (ROIC). A prototype device showed high sensitivity at visible to SWIR wavelengths and low dark current."