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outdoor thermal imaging devices - hunting, hiking, search and rescue

see also:

  • I don't sell any of these nor do I receive any remuneration if you buy them, and I have not personally reviewed all of them, they are listed here to give you perspective
  • this page was created in 2021 and products and some prices reflect those available in 2021!
  • these devices are fantastic for the main use cases but do have major limitations:
    • cannot see through glass windows as these are highly reflective to thermal IR wavelengths so you can't use them from inside your car either - glass windows act as mirrors with thermal imaging devices
      • thus unlike a near IR night vision device, a thermal clip on scope cannot be added to the rear of an optical rifle scope as this would block the far IR from hitting the thermal imager, but they must either be used instead of a rifle scope or clipped onto the FRONT of the scope in which case they need to be 1x magnification to function well
    • cannot see through fabrics (including polyester, nylon, cotton), clear TPU (0.2mm thick or more), animals, humans, trees, leaves, rocks, tents, hiking tarps, walls, conductive materials such as aluminium foils (eg. space blankets) or concrete
      • may be able to see through PVC (sheet or box), 1-2 layers of a garbage bag, plastic bags and through mesh although image is not as clear and there is also minimal transmission through 0.1mm TPU
      • may be able to see through fog, rain, snow, smoke, hot dust, blowing sand
        • fog impairs thermal visual detail of surroundings as most things become the same temperature so you will need a sensor with sensitivity < 40mk to give good results in these conditions
    • cannot see through water - so you will only see aquatic animals when they are on the surface
    • the thermal images are generally NOT as good as near infra-red devices for identifying the type of animal
      • do not generally display enough facial detail at some distance to identify individual persons other than by their clothing
    • warm blooded animals are much harder to discriminate from surroundings on warm days over 20°C
    • do not detect reptiles well as they are cold-blooded and have similar temperatures to surroundings
    • do not work well at ambient temperatures below 0 deg C as most of the natural environment will have similar temperatures
  • DO NOT point it at the sun, lasers, or bonfires as this could permanently damage the sensor!
    • this is a particular risk when you are at full zoom looking in the sky near the sun, as you will not realise the sun is hitting the sensor just out of your zoomed in section
    • fortunately, uncooled vanadium oxide detectors (VOx microbolometers), which are the majority of the sensors on this page, the burn-in from the sun is generally non-permanent, but may take a few days to recover
  • outdoor hunting thermal devices generally do NOT have software that will allow display of an actual temperature!

Introduction

thermal imaging devices

  • warm blooded animals give off IR at around 9-10µm (wave numbers between 1100 to 1000 cm-1)
  • these generally measure far IR wavelengths of 7-14µm (wave numbers between 1400 to 700 cm-1)
    • for comparison, near IR night vision devices work in the IR wavelengths shorter than 1µm and it is in this range hot objects start becoming visible to our eyes such as red hot coals on a fire which are ~600degC
  • these thermal imaging microbolometer arrays are commonly found in two sizes, 320×240 pixels or less expensive 160×120 pixels hence the images are very low resolution, but recently, the ideal is now the more expensive 640×480 pixel sensors
  • the standard commercial models are non-cooled microbolometer sensor arrays are usually vanadium oxide (VOx)
  • there are very expensive but coming down in price while technology is rapidly improving
  • even more expensive and heavier are cooled devices which give much further range and are primarily used by the military
  • they are manual focus
  • they are primarily used for:
    • detecting warm blooded animals including humans day or night
      • however, in general, all one sees is the shape - there may be very little detail especially at a distance - so one may be able to identify what type of animal it is and see how it is behaving, but unless reasonably close, it is unlikely that detail is sufficient to recognise who it is
      • cold blooded animals will generally be camouflaged thermally with its surroundings and are thus generally hard to visualise
      • even warm blood animals can be difficult to distinguish amongst trees when ambient temperatures are over 20degC (human skin tends to be 23degC)
      • see https://www.treehugger.com/hot-and-wild-thermal-images-of-animals-4868612
    • detecting temperature differences on objects
      • areas of heat loss / poor thermal insulation
      • areas of excessive heat / poor electrical wiring, etc
    • use at home
      • finding your cat hiding from you at night
      • finding wildlife in your trees such as possums and birds
      • identifying hot spots in appliances and cords which may indicate either a current is flowing (is the cable broken or not, is there power flowing) or there is a local short circuit or over-heating problem
      • potential health issues such as identifying local inflammation or poor circulation
    • use in camping / hiking
      • navigating at night or in dense fog/cloud
        • much easier to see landmarks in the distance
      • search and rescue - finding an unconscious hiker is made so much easier with a thermal imager (although not so good when temperatures are above 20degC)
      • finding wildlife - searching for often well camouflaged and nocturnal animals to observe their behaviour or to photograph them with your usual telephoto camera (and a flash)
        • an invisible thermal camera is far less stressful for wildlife than shining bright torches at them!
      • camping safety at night - be on the look out for predators - human or animal
    • driving assistance at night or in fog
      • can better identify people or animals and can see through oncoming headlight glare in fog but will not work through your windscreen as this blocks thermal IR so needs to be mounted externally and use WiFi to your smartphone

Important features to consider

  • what base magnification do you need?
    • the thermal scope on your rifle should have a base magnification optimised for your target size and distance, thus 2x for rabbits at 30m, perhaps 4x for foxes at 150m
      • do not use the thermal scope on your rifle for wide fov spotting as you will point your rifle at something you would prefer not to - like a farmer who won't appreciate it! Use a separate wider fov scope for spotting or stalking.
    • what is your usual hunting ground - forests vs open plains
    • if you want to walk as you view the image then a wider fov in a monocular is important perhaps 17deg or wider
    • if you are shooting foxes at 300m then a fov of under 10deg for a rifle scope combined with digital zoom and a 600+pixel sensor would be best
    • this means the 12deg fov devices are probably best as rifle scopes for closer targets
    • a 35mm lens on a 640px sensor or a 19mm lens on a 320px sensor will give a base field of view (fov) of approx. 12.5°×10.0° which equates to ~2m wide at 10m
  • thermal spectral sensitivity will determine how well it can detect differences in temperature
    • look for one that has a NETD less than 25mK or even <18mK for the best background detail
    • <15mK sub$AU5000 consumer devices produced in 2024
    • <20mK sub$AU5000 consumer devices produced in 2023
    • <25mK sub$AU5000 consumer devices produced in late 2021
    • <35mK sub$AU5000 consumer devices produced in late 2020
    • <50mK sub$AU5000 consumer devices produced in 2019
  • frame rate will determine how fast the screen will update - for hunting you should go for at least 30Hz whereas for industrial use under 10Hz is fine
  • pixel size - in general, the smaller this is for a given technology, the more image noise although the latest sensors with 12 micron pixels are very good.
  • sensor resolution and size - the larger this is the more expensive and more image detail and digital zoom and the fov will become wider for same size lens
    • if you are wanting it for hunting then you should aim for a <20mK 640×512 pixel sensor with a nice big display and replaceable batteries
  • display resolution - larger resolution displays - most modern images have a 1280×960 display
  • lens field of view and focus characteristics
    • for hunting or search you will want a narrower fov (ie. more optical zoom)
  • weathersealing most are IP66/67
  • drop resistance - most are rated at 1m, a few at 2m
  • battery life
    • ideally it should have a replaceable 18650 lithium battery or better
  • battery recharging
  • can you replace the battery?
  • can it save videos and stills?
  • can you adjust sharpness and contrast (some have a extra clear mode as a preset)
  • what palettes can you use?
    • most have white hot, black hot, red hot, false colour (“fusion”, rainbow“, etc)
    • some allow you to customise your own palettes
  • does it have a laser to show your colleague the target you have detected (some, such as the Guide Track series allow attaching one via Picatinny rail)?
  • does it have a laser rangefinder to estimate distances to a target?
    • InfiRay Finder models do have this.
    • NB. these require a relatively large and minimally reflective flattish surface angled 90deg to laser such as a tree trunk and generally max out at 600m but probably wont work on a fox further than 450m
  • does it have a IR eye detect auto on/off for eyepiece display?
    • InfiRay Finder models do have this.
  • how well does the lens cap stay on and stay away from the lens when removed?
  • how comfortable is the eyepiece rubber and is it only designed for the right eye?
  • can it accurately provide a temperature measurement?
    • almost none of these give a measurement presumably as they are optimised to separate the thermal ranges within the field of view and are not calibrated to actual temperatures
    • Infiray DV DL13 can do so -20deg to 400degC;
  • is it the latest technology?
    • technology in this area is rapidly improving bring higher quality imagery at lower costs
      • the latest imagers under $AU6000 use a sensitivity under 15mK

Field of View - lens focal length vs sensor size and resolution

The following is as at August 2021, example prices are in $AU:

  • most have 40-50Hz refresh rate, 16Gb internal memory, still/video recording, WiFi smartphone app control, USB charging, diopter, some degree of weathersealing, stadiometric rangefinder (InfiRay includes humans)
  • most have a fixed internal battery which tend to range 5-7hrs but some have user replaceable ones such as Cabin CBL19, most Pulsars
  • all have basic range of thermal palettes of black, white, red hot and colour mode
    • some have Hot Track mode which puts a marker on the hottest object (eg. Guide IRTrack)
    • Pulsar tend to have the best operating system and functions
  • some have built-in laser rangefinder eg. FL25R, FH25R
  • 50mK have nice subject background separation but generally blurry, low contrast uniform backgrounds which can make ascertaining location features more difficult unless you know the terrain
  • the lower the mK have the most background detail and contrast
  • some of the latest models have digital image stabilisation
  • a “1x” magnification equates to around 90mm lens fov on a full frame camera
sensor: 17µm 400×300 17µm 384×288 17µm 640×512 12µm 256×192 12µm 320×240 12µm 384×288 12µm 640×400 12µm 640×512
pixels 0.12mp 0.11mp 0.33mp 0.05mp 0.076mp 0.11mp 0.26mp 0.33mp
35mmFF equiv crop factor 4.7x 4.9x 2.7x 10x 8.5x 7.1x 4.2x 3.9x
examples Guide TrackIR (<50mK) / Nano (<50mK) Pulsar Axion 2 (40mK); Pulsar Helion 2 XQ (<40mK); HikMicro Owl OH (<35mK); HikMicro Owl OQ <35mK HikMicro Lynx LE; Night Tech XD-Mini-II <35mK Pulsar Axion InfiRay E3 (<40mK), Cabin CBL19 (<40mK), FL25R (<40mK); Night Tech XD II (<35mK); HikMicro Lynx LH (<35mK) Guide TrackIR Pro (<50mK) InfiRay E6 v2 (<40mK) E6v3(<25mK), FH25R (<40mK); Night Tech XD Pro-II (<35mK)
10mm lens 18.0° × 13.6° (1.4x) 460m
13mm lens 23.6°×20.7° Infiray DV DL13 smartphone monocular <60mK temp measurements $1394 13.5° x 10.1° 700m Night Tech XD-Mini-II $976
15mm lens 11.7°×8.8° (2.2x) 700m 17.5°×13.1° (1.5x) 700m LH15: $AU1,499
19mm lens 19.0°×14.5° (1.2x) Guide IR510 Nano N1 $AU1885 Pulsar Axion Key XM22 22mm $1895 No Recording! 13.8°×10.4° (1.9x) 900m LH19, CBL19: $AU2299; 22.9°×17.2° (1.1x) 800m Guide TrackIR 19 Pro:
25mm lens 15.4°×11.6° (1.7x) 700m Guide IR510 Nano N2 $AU2265; Guide TrackIR 25: $2500 14.9°×11.2° (1.7x) 900m; OH25: $AU2599; 10.5° × 7.9° (2.5x) 1200m E3: $AU2299; CBL25: $2599; FL25R $AU2799-2999; LH25: $AU2599; 17.5°×13.1° (1.5x) 1000m Guide TrackIR 25 Pro: 17.5°×14° (1.5x) 1300m FH25R: $AU3549-3799
30mm lens Pulsar Axion XM30S 2.5x $3300;
35mm lens 11.1°×8.3° (2.3x) 1000m Guide TrackIR 35: $AU2775 10.66° × 8° (2.5x) OH35: $3299 Thunder TH35 rifle scope $3750; Tracer 35LRF; 17.7°×14.2° (1.4x) 1200m OQ35: $AU4999 7.5°×5.7° (3.5x) 1800m E3: $AU$2,849 XD35-II: $2499 HikMicro Gryphon GH35L fusion $3999 12.5°×9.4° (2.0x) 1400m Guide TrackIR 35 Pro:$AU4795 12.5°×10.0° (2.1x) 1800m iRay Nocpix FH35R E6: $AU3799; E6+ v3 25mK $3899; Night Tech XD-50 II Pro: $AU3899 HikMicro Gryphon GQ35L Fusion $AU5749
38mm lens 10.7°×8° (2.3x) 1200m Axion 2 XQ38 LRF: $3595; Helion 2 XQ38F: $AU3999
40-42mm lens 15.2°×12.3° IAiming 617 rifle scope $AU4200 10.4 x 8.3° (2.5x) iAiming iA-612 rifle scope $5265; 3000m Leica Calonox View $6900
50mm lens 7.8°×5.8° (3.3x) 1400m Guide TrackIR 50: 7.5°x5.6° (3.5x) 1800m Pulsar Helion 2 XQ50F $AU4500 Tracer 50LRF; Pulsar Helion 2 XP50 Pro 640×480 <25mK 2.5x 1800m $AU7850 XD50-II: $3135 8.8°×7.0° (3.0x) 2600m E6: $AU4,299 E6v3 25mK $AU4399; NightTech XD-65 II Pro: $4600; HikMicro Thunder TQ50 <35mK rifle scope

Figures in brackets is the base optical zoom magnification factor compared to naked eye (1x = ~90mm lens on a full frame camera). Figures in meters is approximate maximum human detection range (recognition range is approximately half this)

  • Detection range is directly proportional to lens focal length for a given sensor pixel size.
  • A 12 micron sensor will give 1.4x detection range of an equivalent technology 17 micron sensor and lens.
  • just as in normal digital photography, the field of view increases as the sensor size in mm increases ie. pixels x pixel size
    • thus a 640×512 sensor with a 35mm lens will give same image quality as same sensor type but 382×288 and 35mm lens but in addition gives you a base twice as wide view while a 382×288 sensor with a 19mm lens will give similar field of view as a 640×512 sensor with a 35mm lens but will not be able to zoom with as much detail

thermal imaging devices for outdoors

main manufacturers

  • Guide Sensmart, a subsidiary company of Wuhan Guide Infrared Co
  • InfiRay iRay is a Chinese manufacturer based in Hefei, China; Australian distributor is in Qld
    • iOS app seems reliable and gives full screen video on an iPad although general app controls are iPhone optimised
    • iRay USA
      • founded in 2000
      • USA distributor of Infiray
      • in late 2024, added its own brand Nocpix some with integrated LRF into main optics
      • 5yr wty
      • if phone app does not connect despite being on device WiFi, turn off Mobile Data on phone
  • HikMicro is a Chinese manufacturer founded in 2016
    • thermal imaging smartphone app is called T-vision not to be confused with HikVision app which is a thermometry app for thermometry devices - presumably doesn't work with night vision devices
  • Pulsar eastern European company which has been making thermal imaging devices for decades and their devices have perhaps the best operating system and menus.
  • NightTech
  • Night Pearl European manufacturer not distributed to Australia
  • Unwin Smart is an Australian manufacturer of iAiming scopes
  • Conotech based in Wuhan, China
  • ATN US manufacturer
    • the latest 4T scopes are excellent <25mK, 16-18hr battery, and have microSD card slots but are heavy at 800g-900g
    • their LT scopes are lighter at around 560g but seems they don't record video
  • FLIR is a US manufacturer

hand held devices without video/stills recording

handheld devices with video and still recording capability

unspecified NETD monoculars

60mK or more NETD devices

50mK NETD monoculars

40mK NETD monoculars and binoculars

35mK NETD monoculars and binoculars

25mK monoculars and binoculars

<20mK monoculars and binoculars

<15mK monoculars and binoculars

cooled imager devices

  • Guide IR 5211 binocular cooled imager
    • 3rd gen MID wave cooled sensor technology; 640×512; spectral band 3-5 μm; thermal sens. 25 mK; continuous optical zoom 2.3°- 7°; 1-4x dig zoom; electronic compass; laser rangefinder; GPS; diopter; 3.5kg; 5hr battery; detects humans up to 6km and recognition to 2.5km; visible light day time camera;
    • https://www.celte.com/image/data/prodotti/DataSheet/Termocamere/5211.pdf
  • Guide IR521 binocular
    • ?same model as above? €30,680.00 ; 2107 model?

thermal plus near IR fusion image devices

thermal rifle scope clip-on monoculars

  • designed to be clipped onto the end of an optical rifle scope
  • these can be often be used as standalone monoculars if they have eyepieces
  • some have Bluetooth remote control via a remote controller or a smartphone
  • usually have replaceable batteries
  • they are more expensive than standard monoculars as they are built to withstand recoil shocks
  • HIKMICRO Thunder TH35 Smart Thermal Scope
    • 2020 model; 384×288 17µm <35mK; 35mm 10.0°×8.0°; 2xCR123A 4.5hr non-rechargeable 3V or rechargeable 3.7V batteries (or RCR123A); 16Gb; WiFi remote live via T-Vision app;
    • exit 6mm; 45mm relief; smooth 1-8x zoom although only 1-2x is really usable so great for rabbits at 30m and foxes out to 150m; 187 × 62.5 × 59.2 mm; 415g excl eyepiece,batteries, 600g incl. batteries and mount;
    • buttons not great for gloved hands and orientation differs to most scopes;
    • menu and palettes not great;
    • can be used in three configurations; a Thermal Weapon Scope, a Handheld Thermal Monocular, and a Thermal Front Add-On (additional Lens System required) but zeroing is suboptimal although this may have been fixed in firmware update (https://straightshooting.com.au/review-hikmicro-thunder-th35-thermal-rifle-scope-is-great-viewing-at-under-4-grand/)
    • $AU3750 ($AU2999 on special)
    • similar specs as the HikMicro OH35 monocular which is $AU500 cheaper but cannot replace batteries
  • Infiray Clip CL42
    • 384×288 17micron 40mK; 42mm lens; BT no WiFi;
    • $AU4199
  • Infiray Clip CH50 v1:
    • 640×512 12micron 40mK; 50mm lens; 510g w/o batteries (v1); no WiFi; 4hr batteries; NB. V2 cannot be used as a handheld monocular;
    • $AU5399
  • Pulsar Krypton FXG50
    • 640×480 12micron; 50mm 8.7 x 6.5deg fov; 16Gb; WiFi; 8hr 6400mAh IPS7 battery packs; 143 х 93 х 76 mm;
    • $AU7260

thermal imaging rifle scopes

optical rifle scopes with embedded thermal image overlay

vehicle roof mounted thermal imagers

  • Infiray M6S19 PTZ Roof Mounted Thermal Camera
    • 640×512 12um; < 50mK; 12V DC; WiFi; Ethernet; 64Gb memory; IP56; 2kg; 133mm x 188mm high; laser rangefinder; gyro stabiliser; auto-defrost; suction cup mount or bracket mount;
    • $AU6499
  • NightRide SCOUT Thermal Vehicle System
    • 384 x 288 25Hz, 28° (H)
    • mounts on roof via magnetic strip (if you have aluminium roof you could use suction caps to create a mount)
    • powered by cig lighter (3W)
    • wireless smartphone 360deg remote controlled panning + tilting
    • continuously automatically captures video displayed on phone, tablet or computer and you can set bookmarks
    • 2.5kg; 7 1/4″x6 3/8″x 6 3/4″
    • $AU4275
    • https://www.youtube.com/watch?v=hwBFY1Bz_K8
  • MH-D Thermal Imaging Driver Assist Kit
    • 384×288 19mm 28°x21° (PAL)
    • mounts on front grill of vehicle no pan/tilt
    • connected to an inbuilt vehicle display or optional 6” LCD display $AU499; no WiFi;
    • 400g; 75mm x 58mm x 68mm;
    • $AU4750

thermal imaging drones

  • DJI Mavic 3 thermal drone
    • 640 × 512 12um thermal camera plus 4/3 CMOS, 20MP sensor has a mechanical shutter
    • $AU8249

More science related to these devices

basic theory

  • warm blooded animals give off IR at around 9-10µm (wave numbers between 1100 to 1000 cm-1) which equates to around 23°C
  • these devices generally detect long infrared light wavelengths in the range 7-14µm and are optimised for detecting warm blooded animals in ambient temperatures of 0-20°C but are NOT designed to give temperature readings
  • 3 micron equates to 693°C
  • 7 micron equates to 140°C
  • 7.6 micron equates to 108°C
  • 8 micron equates to 89°C
  • 10 micron equates to around 17°C
  • 10.6 microns equates to 0°C
  • 12.5 micron equates to minus 41°C
  • 14 micron equates to around minus 66°C
  • a body radiates heat in various frequencies of e-m radiation, and its peak frequency becomes higher in proportion to the temperature of the body and can be calculated from Wien's displacement law:
    • temperature in Kelvin = 2897.2/(peak wavelength radiated in microns)

how they work

  • the sensor itself is a vanadium oxide film which has intrinsic sensitivity to infrared wavelengths of 7-14 microns and the intensity of heat hitting each pixel gets translated into an output value which is then further processed
  • the germanium lens further restricts the wavelengths to block wavelengths below 7.6 micron and have reduced response beyond 12.5 microns
  • to improve spectral sensitivity, they may also have:
    • narrowband filters
    • additional cutoff filters

why can't they measure actual temperature?

  • they are generally not optimised to measure actual temperature but to display relative temperatures and are optimised to display warm blooded animals
  • very few have this function, but even if they do have software algorithms to display an actual temperature, accuracy of temperature measurement requires understanding:
    • the thermal emissivity coefficient for that object
      • very few objects act as black body objects and physical objects will have an emissivity of between 0.01 and 0.99 and thermography is likely to be extremely inaccurate if the object has emissivity less than 0.5
      • some thermal emissivity coefficients:
        • highly polished metallic surfaces such as copper or aluminum usually have an emissivity below 0.10
        • roughened or oxidized metallic surfaces will have a much higher emissivity of around 0.6
        • flat-finish paints are around 0.90
        • human skin and water are about 0.98
      • some thermal devices designed for thermography measurements allow you to enter the object's emissivity and the ambient temperature and will adjust the readings to allow for reflection of this ambient temperature as well as the object's emissivity
    • other potential errors in thermography measurements:
      • reflection from the object of a nearby heat source especially if the object has low emissivity

why are they not as good at identifying animals at night as a near IR night vision device?

  • a near IR device “sees” animals much the same way as we see, so they whole animal is visualised reasonably well
  • in contrast, a thermal imaging device displays the thermal pattern of the animal - much of which may be dark due to the fur and tail being colder than the face area which is bright and so you have less of an overall image
  • in addition, thermal imaging devices have much lower resolution than near IR night vision devices so you have much more pixelation on zooming in and less clarity and detail

why are they better than near IR night vision devices for detecting animals at a distance?

  • near IR night vision devices rely on shining an infra-red beam at the animal and detection often depends on eye reflection and thus may need the animal to be looking at the viewer, and the further away the animal is, the stronger the IR light beam needs to be
    • in addition, many near IR night vision devices use an automatic exposure system which can make the subject very dark if it detects the IR light beam hitting foreground foliage which will be much brighter than a distant subject (light intensity falls with the square of the distance travelled)
  • thermal imaging devices on the other hand do not use IR light beams shone at the subject but detect the thermal light given off by the animal, many such devices are rated at detecting a human at 1.8km - but identifying what sort of animal it is may be problematic even at much closer distances

why are they not so good at detecting animals on warm days?

  • warm blooded animals including humans tend to have skin temperatures around 23degC (or higher if ambient temperatures are higher)
  • on warm days above 20degC, most objects such as trees and grass have temperatures similar to skin temperatures and although animals can be seen, they do not stand out from their environment anywhere near as well as when the environment is significantly cooler than them

why are they not so good in very cold situations?

  • when temperatures approach 0degC, (this equates to IR wavelengths of 10.6 microns), most of the environment will end up being displayed as similar temperatures as the device is not optimised to separate minimal differences in temperatures at this temperature

why are they not so good at detecting reptiles?

  • reptiles are generally “poikilothermic” in that their temperature is close to the ambient temperature and thus they do not stand out from their environment very well as this has similar thermal wavelengths

why can't they see through normal window glass?

  • these devices generally detect long infrared light wavelengths in the range 7-14µm (wave numbers between 1400 to 700 cm-1)
  • standard house soda lime float window glass blocks IR at wavelengths longer than 2.8 microns (reducing transmission to 30% for IR up to 4nm) plus it is very reflective
  • thermal imager optics are thus made from special glasses such as:
    • 120 nm - 6.0 μm –> Magnesium Fluoride(MgF2)
    • 150 nm - 5.0 μm –> Sapphire
    • 180 nm - 8.0μm –> Calcium Fluoride(CaF2)
    • 1.2 - 8.0 μm –> Silicon (Si)
    • 2.0 - 16 μm –> Germanium (Ge) hence this is the most common glass for thermal imagers for hunting
    • 600 nm - 16 µm –> Zinc Selenide (ZnSe)

how well do they "see" long distances?

  • they can generally see through fog or high water vapour situations better than we can see
  • the air at sea level blocks IR light from 5.5-7.5nm and above 14microns but thermal devices fortunately use 8-14micron range where the transmission over a 1.8km is mainly around 60-80% although diminishes as one goes past 12microns2)

Spectral transmittance of the atmosphere over 1 nautical mile at sea level (1.8km) courtesy of Newport.com

how good are the laser range finders?

  • they are generally reasonably accurate in low light conditions from a close range of around 10m to a distance of 200-800m depending upon the model, as long as the subject is relatively flat matt surface (eg. tree trunk or animal) which can reflect back the laser beam
  • they tend to be less useful in bright sunlit conditions
1)
https://www.youtube.com/watch?v=v9b9Wf2RCos
2)
https://www.newport.com/n/thermal-imaging
photo/thermal_imagers_outdoor.txt · Last modified: 2025/04/14 08:23 by gary1
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